WEBVTT 1 00:00:06.430 --> 00:00:07.630 Mark Kushner: 6. 2 00:00:24.720 --> 00:00:27.930 Mark Kushner: That's great. Good afternoon. 3 00:00:28.040 --> 00:00:44.790 Mark Kushner: I'm. Frederick introduced Dr. Eve Stemson as our misty speaker this afternoon he'd received her Phd. Working with Paul Bellen at Caltech. So it's a dynamic of arch plastic field flux to generated by pulse power magnetized plastic guts. 4 00:00:44.860 --> 00:00:46.990 Mark Kushner: His current interests are many. 5 00:00:47.230 --> 00:00:56.670 Mark Kushner: The major focus and electron plasma. She is now scientists and group leader at the Max Pike Institute of the class of Physics in Germany. 6 00:00:56.750 --> 00:01:00.610 Mark Kushner: where she coordinates the International apex collaboration. 7 00:01:00.680 --> 00:01:13.360 Mark Kushner: The most recent addition is E. Posts, electrons, and positrons, and the optimized celebrator. you've received the hans we're in a Austo class of physics prize in 2,021 8 00:01:13.570 --> 00:01:17.360 Mark Kushner: for pioneering. Experimental research on 9 00:01:17.880 --> 00:01:28.680 Mark Kushner: other scientific interests include open source like temperature measurement systems and through spots for them in essence and magneto resistive semiconductors. 10 00:01:28.920 --> 00:01:43.050 Mark Kushner: It has been quite active, and Aps division and positive physics from both technical and administrative perspectives. She recently chaired the Committee on on Concerns of students and early career of scientists. 11 00:01:43.310 --> 00:02:02.080 Mark Kushner: The title of these talk today is the apex, a positron electron experiment, collaboration, progress and future developments. But prior to you're giving this seminar, we have a token of our appreciation out of you coming to Ann Arbor. It's the official nipsy mug. 12 00:02:02.500 --> 00:02:04.990 Mark Kushner: and we need to record this august moment. 13 00:02:10.699 --> 00:02:13.070 Mark Kushner: Thank you very, very much. 14 00:02:13.260 --> 00:02:26.710 Mark Kushner: I'm looking forward to taking it back to Germany and drinking coffee there, and I also brought some German candy, so they have some gummies and chocolates. So afterward, if we need some additional dessert. 15 00:02:26.790 --> 00:02:29.570 Mark Kushner: then you're welcome to to come on by. 16 00:02:32.260 --> 00:02:48.570 Mark Kushner: So thank you very, very much for having me and giving me the opportunity to tell you about what we've been working on in the apex collaboration. I have a a few pictures on the title slide of some of our experiments or calculations. And 17 00:02:48.600 --> 00:03:03.320 Mark Kushner: so we have overall. We have a series of experiments, each of which would probably be considered like a university scale experiment. But we're stringing them all together in hopes of making electron positron plasma within the next couple of years, ideally 18 00:03:08.280 --> 00:03:12.610 Mark Kushner: get the focus back there we go. So the apex collaboration. 19 00:03:12.980 --> 00:03:22.140 Mark Kushner: as mentioned, apex stands for a positron electron experiment, and we're based at the Max Punk Institute for plasma physics. 20 00:03:22.440 --> 00:03:29.640 Mark Kushner: But we have collaborators at universities and institutes in Germany and around the world. 21 00:03:29.680 --> 00:03:45.540 Mark Kushner: including across the Us. And Japan and a growing group of alumni. So the the work I'll be presenting includes contributions from all of the people on this line, and and a few others that are mentioned individually. 22 00:03:45.540 --> 00:03:50.380 Mark Kushner: So it's very much a group effort, and i'm honored to be able to tell you about it 23 00:03:51.980 --> 00:03:56.820 Mark Kushner: so to to give you an overview of what i'll go through today. 24 00:03:56.860 --> 00:04:15.170 Mark Kushner: First, I will introduce you to the compelling goal of laboratory per plasmas. What they are. Why, we want to make them. Some approaches to making them, and then how exactly we're hoping to go about this in the apex collaboration. So getting enough positrons. 25 00:04:15.250 --> 00:04:19.680 Mark Kushner: finding tr to put them with electrons, and then filling in a few gaps in between that 26 00:04:20.339 --> 00:04:35.080 Mark Kushner: and then the last part. I'll show you some of our recent progress toward that goal which hopefully, by then we'll have given the framework for showing why we're doing some of these things that we've been doing, and why we're excited about some of the progress that we've made 27 00:04:37.530 --> 00:04:54.030 Mark Kushner: so first to orient you about where apex is in the plasma universe. So, as I mentioned, our goal is to combine electrons and positrons to make some usually unusual, but likely very interesting plasma. 28 00:04:54.040 --> 00:04:56.150 Mark Kushner: That's half matter in him, half antimatter. 29 00:04:56.660 --> 00:05:13.530 Mark Kushner: and the type of plasma that we're going to make. In addition to being a pair plasma, so half matter on handcap anti-matter is going to be very low density and relatively low temperature so this purple star is our target for the plasma that we want to make. 30 00:05:13.840 --> 00:05:24.170 Mark Kushner: and then the orange stars show some typical lab ass and physics experiments from post-power gas or from post wire arrays. 31 00:05:24.220 --> 00:05:29.270 Mark Kushner: and then standard temperature and pressure is over here. and 32 00:05:29.740 --> 00:05:40.050 Mark Kushner: and unfortunately I I haven't added a star for low temperature, plasma, and atmospheric plasma, but they would also be more closer to the the bottom. Right? 33 00:05:42.860 --> 00:05:43.970 Mark Kushner: So 34 00:05:44.110 --> 00:05:51.520 Mark Kushner: plasma, terror, plasma, I would like to argue, are an exciting frontier in plasma physics, because mass asymmetry 35 00:05:51.520 --> 00:06:06.850 Mark Kushner: is built into plasma physics from the ground up. So if you think about the physics of normal quasi-neutral plasma, you have your ions, and you have your electrons, and you have this large separation of your time scales, and your life scales due to the mass asymmetry. 36 00:06:07.200 --> 00:06:19.660 Mark Kushner: So I have a cartoon of lmer orbits, and then a law blog plot of the velocity distribution function for protons and electrons. If you assume that they're the same temperature 37 00:06:20.330 --> 00:06:32.010 Mark Kushner: so normally in the plasma, you have the fast phenomena involving the ion motion and the slow phenomena involving Si tasks involving the electron motion and the slowing phenomena involving the ion. Motion 38 00:06:32.030 --> 00:06:33.710 Mark Kushner: and this 39 00:06:33.720 --> 00:06:36.120 Mark Kushner: it is what is, what class of physics is built on. 40 00:06:36.420 --> 00:06:44.800 Mark Kushner: But what if all of the charged particles in your plasma had the same mass? What if the mass ratio, instead of being on the order of 2,000 or more, we're going to be. 41 00:06:45.290 --> 00:06:57.540 Mark Kushner: This question was first raised more than 40 years ago, and since then has generated on the order of a 1,000 papers on how plasma physics is different when everything is the same mess. 42 00:06:58.020 --> 00:07:03.960 Mark Kushner: and most of These papers are in theory and simulation, because making pair plans in the lab is very difficult. 43 00:07:03.990 --> 00:07:14.230 Mark Kushner: And so we're we're part of that effort. We're not the only ones. There are a number of different approaches to trying to make per plasmas, and and and they they tend to be complimentary. 44 00:07:15.450 --> 00:07:25.260 Mark Kushner: But to give a taste of some of the predictions for how her plasma is are different. There are some ways where periplasmas are the same as normal plasma is. There's just like 45 00:07:25.290 --> 00:07:34.950 Mark Kushner: a factor of 2 or a square root of 2 and otherwise otherwise it's the same. But there are other way. Other aspects that where dramatic changes are predicted. 46 00:07:35.060 --> 00:07:43.980 Mark Kushner: such as not having things like Whistler ways or lower hybrid wave, some of the standard waves that you expect to have, and your typical electron I am plasmas 47 00:07:44.230 --> 00:07:53.150 Mark Kushner: or changes in the characteristic properties of more complex phenomena, like reconnection or turbulence. 48 00:07:53.220 --> 00:07:57.880 Mark Kushner: I'm particularly interesting for people in the business of man that confinement 49 00:07:57.950 --> 00:08:07.670 Mark Kushner: in the geometry that our pair plasma is in in the regime where our pair plasms are going to be. So this relatively low temperature, very low density, regime 50 00:08:07.690 --> 00:08:10.300 Mark Kushner: and strong magnetic fields. 51 00:08:10.350 --> 00:08:17.830 Mark Kushner: her plasma are predicted to have remarkable stability properties. whereas a fusion plasma or an electron or a low 52 00:08:17.990 --> 00:08:30.550 Mark Kushner: density, low temperature, electron. I am plasma in this regime would develop turbulent instabilities that help it to week out of the container faster than you would expect it to otherwise. 53 00:08:30.580 --> 00:08:45.090 Mark Kushner: Her plasma is in this regime are expected to have remarkable stability properties, so to not develop turbulence, which would be really something to see given how plasma is in general like to develop turbulence fluctuations. 54 00:08:46.060 --> 00:08:57.360 Mark Kushner: And so, as an illustration of what part of why, that's the case. If you think about an electron Ion plasma where you have your you start off 55 00:08:57.380 --> 00:09:02.460 Mark Kushner: with your particles distributed here. So a a perturbation in your density. 56 00:09:02.810 --> 00:09:19.450 Mark Kushner: and then you let it go. Then the electrons stream out, leaving behind the ions, and that develops that that creates an electric field. So you get this coupling between pressure perturbations and electric field perturbations and electron ion plasma, whereas if everything were the same mess, it just streams out. 57 00:09:19.450 --> 00:09:26.780 Mark Kushner: and you don't get the same coupling. And so that's the basis of Why, some of these turbulent fluctuations Aren't expected to develop in the same way. 58 00:09:28.150 --> 00:09:31.240 Mark Kushner: and I can show the movies later if we want to. But for now i'll 59 00:09:31.320 --> 00:09:33.870 Mark Kushner: keep things rolling. So 60 00:09:34.020 --> 00:09:49.730 Mark Kushner: the if we think about basic plasma waves I some of the students I was talking to you today mentioned that you've recently looked at the cma diagram in class you think about. So you have this this landscape of basic plasma waves 61 00:09:49.850 --> 00:09:57.350 Mark Kushner: where you move in density on the x-axis and the magnetic field on the Y Axis in terms of the frequencies 62 00:09:57.400 --> 00:10:00.800 Mark Kushner: of your cyclotron frequency and your plasma frequency. 63 00:10:01.360 --> 00:10:16.430 Mark Kushner: And you've made all of these simplifying assumptions about your plasma. You've assumed that it's homogeneous, but it's infinite, that it's magnetized in the Z direction that you can describe it as 2 frictionless fluids with with 0 temperature, and you're only looking at linear modes. 64 00:10:16.620 --> 00:10:23.420 Mark Kushner: and you still end up with this whole zoo of different waves that you can get out of these depending on what frequency you're looking at. 65 00:10:24.250 --> 00:10:38.400 Mark Kushner: So if we think about how this diagram, so you have all of these resonances and cut offs in the normal cma diagram that, and these tend to depend on the mass ratio. So what happens then? If your mass ratio is unity. 66 00:10:38.690 --> 00:10:40.440 Mark Kushner: you get a much simpler diagram. 67 00:10:41.460 --> 00:10:43.830 Mark Kushner: So you you have 68 00:10:44.090 --> 00:11:01.900 Mark Kushner: many fewer options, and in addition, as this more subtle point, the your wave normal surfaces always touch at the top and bottom, so in the direction of the magnetic field, so you can have it most 1 one way propagating along the magnetic field. So this is one example of how 69 00:11:01.900 --> 00:11:09.600 Mark Kushner: a pair plasma is this kind of quintessentially symmetric plasma that's supposed to make things a little bit more tractable. 70 00:11:11.580 --> 00:11:18.040 Mark Kushner: So if we're not talking about like Platonic forms of plasma. And thinking about real plasma is, how does this help us? 71 00:11:18.450 --> 00:11:33.280 Mark Kushner: Well, it's actually already been well established that by varying the mass ratio and simulations that helps us to tease out what effects are or aren't important. And so the picture on this slide is about took a Mac turbulent transport. 72 00:11:33.550 --> 00:11:42.860 Mark Kushner: where previous simulations that used a reduced mass ratio weren't, able to reproduce the experimental levels of transport. 73 00:11:43.220 --> 00:12:00.350 Mark Kushner: and only by doing simulations at the full mass ratio where the experimental levels able to be reproduced. So that's where the experimental level is the dashed line. This is the the heat transport, and it turns out that the electron scale turbulence 74 00:12:00.350 --> 00:12:05.460 Mark Kushner: is more important than thought. So, instead of being washed out and dominated by the Ion scale turbulence. 75 00:12:05.490 --> 00:12:12.770 Mark Kushner: it it still plays a role, and it was by doing the full mastery of the simulations that they were able to figure that out. 76 00:12:13.930 --> 00:12:21.690 Mark Kushner: Another example of how bearing the master ratio helps you figure out what isn't as important is reconnection phenomena. 77 00:12:21.700 --> 00:12:35.320 Mark Kushner: So this is from a paper where they did simulations at different mass ratio of magnetic reconnection and sounds that the rate at which magnetic field lines reconnected didn't actually change very much when they did this. 78 00:12:35.380 --> 00:12:39.570 Mark Kushner: although some other, there were some other changes to the current structure. 79 00:12:39.620 --> 00:12:58.080 Mark Kushner: and that suggests that with their waves aren't as important to magnetic reconnection as expected, because the as mentioned with the waves, Don't exist at all in the pair plasma, and so it reduced mass ratio you'd expect, if with their waves, where the dominant factor for varying the mass ratio to change the reconnection rate. 80 00:12:59.720 --> 00:13:17.420 Mark Kushner: And then, as a a more general comment, we know that in physics it's important for us to understand our limits, and some of the amo physics. Physicists that I talk to about per plasma is when i'm explaining that their plasma is this simple version of a plasma. We have Lots of predictions about 81 00:13:17.490 --> 00:13:30.660 Mark Kushner: things are usually a lot more complicated, but we want to make sure that we can really understand their plasma, They say, oh, it's the hydrogen atom of plasma physics, the simple system. We want to be able to to make sure. We understand that one really well, and then go from there 82 00:13:31.730 --> 00:13:36.590 Mark Kushner: and then. This is one more thing along those same lines. Sometimes 83 00:13:36.650 --> 00:13:44.350 Mark Kushner: theory folks will say, Well, why even bother is so simple. We know what you're going to get, or why not just simulate the whole thing. 84 00:13:44.740 --> 00:13:58.390 Mark Kushner: And this was a a quote from Stuart Craiger from a winter school that I went to back when I was a grad student, and all of the previous speakers had been talking about their simulations, and sometimes referring to them as experiments. 85 00:13:58.390 --> 00:14:16.870 Mark Kushner: And so he had this cheeky comment, that experiment can simulate computation. Resolving all scales, including all correlations, Mhd. And kinetic effects with the CPU time of under a second. We actually hope to have our plasma in there for longer than a second. But this the spirit still holds. 86 00:14:16.960 --> 00:14:18.750 Mark Kushner: and 87 00:14:18.870 --> 00:14:22.620 Mark Kushner: we know, you know, from doing experiments that sometimes 88 00:14:23.350 --> 00:14:31.470 Mark Kushner: terms that you expected to be important or not not to be, or the other way around. Sometimes they workforce or better than you expected. 89 00:14:31.510 --> 00:14:49.560 Mark Kushner: and Sometimes a system may start in one regime, and then evolve to cross the boundary into another like this example, for both from one of my grad school colleagues for her system, and he initially started being well described by Mhd. And then crossed into a territory where, due to an instability that resulted in reconnection. 90 00:14:51.240 --> 00:15:08.950 Mark Kushner: So this is the sort of summary of the pitch for Why, I think periplasm is this really compelling thing to study? Is that laboratory tests of predictions for them represents exciting new territory that can test in advance or understanding of fundamental aspects of plasma. 91 00:15:08.950 --> 00:15:19.800 Mark Kushner: And in addition, there are a lot of electron positron plasma. Out there in the universe we see more than 10 to the 43 positrons in the islanding every second 92 00:15:19.900 --> 00:15:22.240 Mark Kushner: these are formed oops. 93 00:15:22.520 --> 00:15:43.000 Mark Kushner: Sorry these are generated around highly energetic. As for physical phenomena, like Gamma Ray bursts and active galactic nuclei. But then you get electron positive from plasma, and maybe by studying them in the laboratory we can learn more about them, although the ones we we will be studying are very far from the relativistic regime. 94 00:15:43.390 --> 00:15:46.450 Mark Kushner: It's still something that also occurs in nature. 95 00:15:48.960 --> 00:15:54.730 Mark Kushner: So how do we make their plasma? So how can one make their plasmas? 96 00:15:55.210 --> 00:16:00.000 Mark Kushner: The first attempts were in the mid nineties, where you had 97 00:16:00.090 --> 00:16:17.130 Mark Kushner: a positron plasma in a non-neutral plasma trap. So these are cylindrical electrodes at the top and bottom. There are end caps that keep a collection of pure positrons in the center. Here this is the same thing, but a different geometry. 98 00:16:17.160 --> 00:16:21.420 Mark Kushner: And then they send an electron beam through. That's density matched. 99 00:16:21.630 --> 00:16:27.930 Mark Kushner: and they actually are. Observe, instability is consistent with a per plasma, 2 stream instability. 100 00:16:28.180 --> 00:16:40.230 Mark Kushner: but because the electrons aren't confined and they get accelerated as they go through the positrons you end up with the the by length for the electron being being larger than the diameter of the electron so 101 00:16:41.900 --> 00:16:47.500 Mark Kushner: you can also produce relativistic pairs with high-powered lasers. 102 00:16:48.110 --> 00:16:54.160 Mark Kushner: So there are a couple of different examples of these. one with 103 00:16:54.280 --> 00:17:04.680 Mark Kushner: laser wakefield acceleration. That's been incidents with, and then the electrons are incident on a solid target to produce pairs, and another where the laser is directly incident on the target 104 00:17:04.970 --> 00:17:06.589 Mark Kushner: to produce pairs. 105 00:17:07.579 --> 00:17:13.010 Mark Kushner: And these experiments initially struggled with charge neutrality, but are now getting 106 00:17:13.030 --> 00:17:15.349 Mark Kushner: to the point where it's close enough 107 00:17:15.380 --> 00:17:21.950 Mark Kushner: to to not worry about it too much more, and simulation suggests that they're getting 108 00:17:22.020 --> 00:17:35.580 Mark Kushner: on the threshold of being able to see collective behavior in state of the art systems. And there's also been some work on looking at trying to trap these relativistic pairs in a mirror. Geometry. 109 00:17:38.380 --> 00:17:58.060 Mark Kushner: Another way to make a pair plasma, instead of using electrons and positron, is to use positive and negative ions, and this was done by a group in Japan that used c. 60, and made so c. 60, plus and c. 60 minus. You can't tell the like. The extra electrons are negligible. The 2 electron difference there. 110 00:17:58.270 --> 00:18:08.560 Mark Kushner: and they were able to look at electrostatic modes. But they also saw some unexpected effects that probably have to do with electron contamination, because the electrons didn't necessarily stay where they were put. 111 00:18:08.810 --> 00:18:14.880 Mark Kushner: And it's also really hard to magnetize a. C 60 plasma, because there that's enormous. 112 00:18:15.760 --> 00:18:26.270 Mark Kushner: So, again, complimentary to some of these other efforts. What our collaboration is trying to do is to achieve many of the bylines with both species magnetically confined. 113 00:18:26.400 --> 00:18:32.180 Mark Kushner: So we want to make sure our de by length is smaller than our device size. 114 00:18:32.420 --> 00:18:40.460 Mark Kushner: and that the lava radius is much smaller than the device size, and it turns out the ler radius ends up much smaller than the d by length, and in our plasma as well. 115 00:18:42.060 --> 00:18:48.580 Mark Kushner: so we want to do. In other words, we want to do low temperature electron positive from plasma in toroidal traps 116 00:18:49.880 --> 00:18:55.890 Mark Kushner: with a magnetic mirror being a another alternative to this that's also being worked on in Japan. 117 00:18:57.780 --> 00:19:07.160 Mark Kushner: so like I said, we need to get enough positron. We need a place to put them with electrons, and we need to figure out some steps in between that. 118 00:19:07.600 --> 00:19:18.740 Mark Kushner: So how many posit phones is enough? I said. We want to use a Toronto device because we want to get. We want to trap both positively and negatively charged particles for as long as possible. 119 00:19:19.060 --> 00:19:36.990 Mark Kushner: So if we have a generic tourist here that has some minor radius and some aspect ratio, which then the product of that is your major radius. We have some limited number of positron to put in there, and we have some temperature and calculate how many 120 00:19:36.990 --> 00:19:42.780 Mark Kushner: we want to make the number of the bylines within the minor radius as large as possible. 121 00:19:43.190 --> 00:19:52.210 Mark Kushner: So what we want to do is that we want to make the device smaller, because then we have less volume to fill with the same number of positrons. 122 00:19:52.420 --> 00:20:02.690 Mark Kushner: More positrons are always good, but we we there are some pretty hard limits on how many we can get. We'd like the temperature to be lower and lower aspect. Ratio also helps us out. 123 00:20:03.250 --> 00:20:05.580 Mark Kushner: and it turns out with realistic 124 00:20:05.670 --> 00:20:10.990 Mark Kushner: sizes for some of these things, I guess, as a small note. 125 00:20:11.020 --> 00:20:12.210 Mark Kushner: if we 126 00:20:12.610 --> 00:20:20.660 Mark Kushner: both the making it small and minor radius and small and aspect ratio are equally helpful. So there's just the same dependence on both of those. 127 00:20:20.800 --> 00:20:30.720 Mark Kushner: and that once you decide about what your you want your volume to be, then you pretty much decide how big you want your device to be. 128 00:20:31.280 --> 00:20:48.950 Mark Kushner: and in principle you could make a plasma with fewer positrons if you make a teeny, tiny pair plasma confinement device. But then you're getting beyond our diagnostic capabilities, and you also have to worry about precision. So so that gives us something that we want to be table top sized 129 00:20:49.000 --> 00:20:52.240 Mark Kushner: as a a balance between the number of positrons we can get. 130 00:20:52.390 --> 00:20:56.680 Mark Kushner: and the challenges of building and diagnosing a tiny experiment. 131 00:20:56.990 --> 00:21:00.100 Mark Kushner: And this is something on the order of tens of leaders 132 00:21:00.130 --> 00:21:04.140 Mark Kushner: with a major radius in the low tens of centimeters. 133 00:21:04.280 --> 00:21:10.520 Mark Kushner: I'm. On your radius of less than 10 cm, and then an aspect, a low aspect ratio. 134 00:21:11.910 --> 00:21:41.070 Mark Kushner: We would like the magnetic field to be very strong, not because we necessarily needed for confinement, but because we would like to be able to take advantage of cyclotron cooling. So we know from other experiments that operate in this regime, that they often have trouble keeping their charged particles at the temperatures they want them to be. They can take a heating that they don't want, and having access to cyclotron cooling which usually starts to become meaningful. Once you get up to around to Tesla 135 00:21:41.080 --> 00:21:47.980 Mark Kushner: helps out a lot with the some of the experimental goals. so that implies that we need super conducting coils. 136 00:21:49.430 --> 00:21:57.240 Mark Kushner: As for for steady state, we'll have a large magnetic field. We will have low plasma densities. 137 00:21:57.410 --> 00:22:07.750 Mark Kushner: because antimatter is quite hard to come by; but as it as it turns out, this puts us in this regime, where we're expected to be able to have collective effects, but not have turbulence. So it 138 00:22:07.900 --> 00:22:09.690 Mark Kushner: should actually work out pretty well. 139 00:22:11.630 --> 00:22:23.100 Mark Kushner: and we also 1, 2, and we'll have low plasma temperatures. We want to have low plasma tensor temperatures to have collective effects. Remember the lower, the temperature, the smaller the by length. 140 00:22:23.180 --> 00:22:36.530 Mark Kushner: We also want to avoid creating unwanted ions from any residual neutrals that are still hanging around in their vacuum chamber. and to avoid a dominant lost channel for the positron which also involves residual neutrals. 141 00:22:37.010 --> 00:22:48.780 Mark Kushner: So, then, this is the the whole rundown of some of the other parameters in terms of a micron scale. Gyro, radius, millimeter, scale by length centimeter scale device. 142 00:22:48.800 --> 00:22:55.240 Mark Kushner: a plasma skin depth, but significantly larger than the device. and they very, very low. 143 00:22:58.290 --> 00:23:07.450 Mark Kushner: since we're putting matter and anti- matter together, and obvious question is, how long it'll actually last, because when you put matter and anti- matter together, they annihilate 144 00:23:08.700 --> 00:23:22.440 Mark Kushner: However, in this very low density regime, the the time. Scales for that to happen are actually quite slow. With the exception of these, a couple of these last channels that involve residual gas. 145 00:23:22.540 --> 00:23:32.760 Mark Kushner: So what this plot shows is how long you'd expect the plasma to last for given density. and in some of these lines a given temperature 146 00:23:34.330 --> 00:23:41.370 Mark Kushner: for depending on lost channel. So if direct annihilation between electrons and ions 147 00:23:41.600 --> 00:23:43.700 Mark Kushner: is, are the purple lines. 148 00:23:43.920 --> 00:23:52.190 Mark Kushner: the blue and the green involve essentially recombination of an electron and the positron to the formation of a bound state 149 00:23:52.440 --> 00:24:09.950 Mark Kushner: which is called positronium. That's the the Ps. And the abbreviation for this bound state of an electron and positron. And once you form positronium, then it'll last, for somewhere between 100 picoseconds and 100 nanoseconds depending on the State unless you excite it. So you don't want to form positronium. 150 00:24:09.950 --> 00:24:18.840 Mark Kushner: and then you don't want to annihilate on your residual gas, and so, if we have as good a vacuum as we should be able to manage, and we keep our temperatures low. 151 00:24:19.170 --> 00:24:34.190 Mark Kushner: We might actually be limited by the symmetry of our magnetic confinement devices, which would be a very interesting thing to be able to study how how much the symmetry affects the plasma transport in the in our, in our toilet traps. 152 00:24:36.430 --> 00:24:45.630 Mark Kushner: And as a note, the this regime that we're going to be in where the llama radius is smaller than the by length smaller than the device is smaller than the plasma skin. Depth 153 00:24:45.710 --> 00:24:51.520 Mark Kushner: is the strongly magnetized weekly couple of regime, which is what Professor Baller's group works on. 154 00:24:53.080 --> 00:24:54.290 Mark Kushner: among other things. 155 00:24:56.170 --> 00:25:04.620 Mark Kushner: so hopefully, we can learn from some of your work. How long? The answer to the question of how long can we expect our Plasma 156 00:25:04.660 --> 00:25:05.490 Mark Kushner: 11? 157 00:25:07.820 --> 00:25:16.550 Mark Kushner: So the the whole grand scheme? This is the schematic of the whole thing. So we, I'll go through it step by step. 158 00:25:16.600 --> 00:25:19.710 Mark Kushner: and this is the the roadmap to keep you oriented. 159 00:25:20.860 --> 00:25:31.330 Mark Kushner: So we first we need to get positive from positron from a world class source. And so that's the red box and the top row first. Here, the high intensity, positron, beam. 160 00:25:31.500 --> 00:25:39.490 Mark Kushner: and the positron beings name is Nepal. and the world's class Positive transfers can give you up to 10 to the 9 positrons per second. 161 00:25:41.150 --> 00:25:56.990 Mark Kushner: And so to explain a little bit more. Here's a little bit of geography. So this is a a map of Germany with the 2 locations of the Max Planck Institute for plasma physics. This the one up here is in the City of Bries full. That's on the Baltic Sea. 162 00:25:57.240 --> 00:26:04.070 Mark Kushner: and the one down here on the northern outskirts of Munich is in the town called Darking Research Center. 163 00:26:04.100 --> 00:26:08.430 Mark Kushner: has a whole bunch of different Max Planck Institutes and scientific 164 00:26:08.530 --> 00:26:12.870 Mark Kushner: research going on here, and this is an aerial view of it. 165 00:26:14.000 --> 00:26:22.840 Mark Kushner: So when you come up from from the subway, you're like, well, it's this way to the center for quantum optics, or it's this way to the one for the Institute for Plasma physics. 166 00:26:24.070 --> 00:26:28.160 Mark Kushner: And if we zoom in on this map in this box here. 167 00:26:28.510 --> 00:26:36.160 Mark Kushner: you see this egg shaped device. That was the original Venic research reactor that was built in the fiftys 168 00:26:36.520 --> 00:26:47.130 Mark Kushner: and operated for several decades, and is actually on the code of arms for the city which you see in the back here. and this is operated by the Technical University of Munich. 169 00:26:47.310 --> 00:26:53.980 Mark Kushner: or it was the new one is now operated by the Technical University of New York, so named F. R. M. 2. 170 00:26:54.090 --> 00:26:59.880 Mark Kushner: It's no longer a reactor. It's now a neutron source, because it's not a good time to be a reactor in Germany. 171 00:27:00.190 --> 00:27:13.450 Mark Kushner: but also because the purpose of this reactor is to make neutrons for scientific research. It's not to make power. And and so it's. It's actually 172 00:27:13.570 --> 00:27:20.940 Mark Kushner: not only politically exceeding, but also quite fair to refer to it as a neutron source, and it started operation in the 2,000, 173 00:27:21.080 --> 00:27:35.570 Mark Kushner: and the Institute for Plasma Physics is right next door. Our offices are here in our lab spaces there. So if if you happen to be visiting for one of the other Institutes, and would like to step on or get a tour. Please get in touch 174 00:27:36.520 --> 00:27:40.470 Mark Kushner: inside the neutron source. This is 175 00:27:40.820 --> 00:27:47.760 Mark Kushner: it's a swimming pool reactor. So there's a light water pool, and then inside that is a heavy water pool. 176 00:27:48.370 --> 00:27:59.690 Mark Kushner: You can see someone looking down into the like water pool. And then there are a whole bunch of different neutron beam lines that come out from the single fuel element in the center 177 00:27:59.830 --> 00:28:17.410 Mark Kushner: and the peak. Thermal neutron flux is actually outside of the the fuel element in the heavy water. They also have liquid deuterium and heated graphite to produce a cold neutron beam and a hot neutron beam, so different thermal distributions of neutrons. There are several dozen neutron instruments there. 178 00:28:17.450 --> 00:28:25.560 Mark Kushner: and sticking in from the side of the heavy water. Pool. You see this beam tube, and if you take a cross section of that beam tube 179 00:28:25.940 --> 00:28:35.780 Mark Kushner: there's the 10 cm scale bar. and this is the beam tube for Nepal month. The neutron induced positron source Munich, and that's positron source. 180 00:28:35.860 --> 00:28:55.750 Mark Kushner: So the thermal neutrons that that reach this cadmium cap are captured and then this results in Gammas admitted from the the cadmium. These Gammas interact with these platinum foils to produce pairs which also lose significant energy in the platinum. 181 00:28:55.750 --> 00:29:17.530 Mark Kushner: and then, by biasing the platinum foils and using my magnetic field guiding coils, the positrons get extracted down the beam lines, and so you can get up to 10 to the 9 positrons per second, that Kev. Or if you want to go down to the the Ev, or tens of vv scale, then you lose. You go down to 5 times 10 to the 7 or so. 182 00:29:20.010 --> 00:29:29.840 Mark Kushner: and if you are outside in this hall, then you can use the neutrons or the positron. So this is. This is the view of the reactor hall. The pool is behind this wall 183 00:29:30.050 --> 00:29:45.170 Mark Kushner: on the lower level, or all the neutron experiments, because those are harder to guide. And then on this upper level. Here is is this zoo of positron experiments, and this orange box. Here is the pipe positron pipe where we get to install experiments, and 184 00:29:45.340 --> 00:29:57.370 Mark Kushner: and we've spent quite a bit of time characterizing and helping develop the being to get the distribution function and the the number of positrons tuned for 185 00:29:57.460 --> 00:30:04.250 Mark Kushner: the the traps that we're going to be using, and also for injecting them into a dipole magnetic field and then trapping them there. 186 00:30:04.410 --> 00:30:16.270 Mark Kushner: But that's just our experiment. There is also a whole bunch of other cool things you can do with positron and surface science, material, science, atomic molecular optical physics. 187 00:30:16.300 --> 00:30:20.130 Mark Kushner: fundamental tests of the standard model and things like that. 188 00:30:21.780 --> 00:30:33.220 Mark Kushner: So but we want to use the positron to make her plasma. So that means we need to. Next use a series of non neutral plasma traps to collect them until we have enough to make a plasma. 189 00:30:33.440 --> 00:30:41.650 Mark Kushner: I I did the the calculation, saying for a given number and temperature, how many we need, and that number turns out to be something like 190 00:30:41.980 --> 00:30:47.080 Mark Kushner: 10 to the 1110 to the 10 depending on the temperature. 191 00:30:47.680 --> 00:30:59.760 Mark Kushner: So that means we need to accumulate positron from that, from at least for tens or hundreds of seconds, and probably for longer if we're using the lower energy beam. And so that's where these traps come in 192 00:31:01.440 --> 00:31:11.010 Mark Kushner: for those who aren't already familiar with non-neutral plasma traps this is a a guide to how they work. You have a uniform magnetic field. 193 00:31:11.230 --> 00:31:18.430 Mark Kushner: and in that magnetic field you create an axial potential. Well using a stack of hollow cylindrical electrodes. 194 00:31:18.790 --> 00:31:21.800 Mark Kushner: and this whole thing is an ultra-high vacuum. 195 00:31:22.120 --> 00:31:25.100 Mark Kushner: and that is a 196 00:31:25.260 --> 00:31:26.790 Mark Kushner: and this trap 197 00:31:27.090 --> 00:31:40.030 Mark Kushner: can trap single particles. So this is a pending trap or a pending mumber trap name for the people who first came up with them, and you can contract. You can trap single particles. You can trap clouds of particles you can trap 198 00:31:40.030 --> 00:31:48.540 Mark Kushner: so many particles of a single sign that it acts like a a fluid. So that's where you call it a non-neutral plasma. You have collective effects with waves. 199 00:31:49.260 --> 00:31:52.480 Mark Kushner: and and so this is a very versatile trap. 200 00:31:52.630 --> 00:32:00.730 Mark Kushner: It works incredibly well. You can trap especially low density non-neutral plasma is here for for weeks. 201 00:32:02.010 --> 00:32:03.200 Mark Kushner: and 202 00:32:03.590 --> 00:32:12.440 Mark Kushner: and this is what one looks like in person. This is these are the electrodes. You can see them on the vacuum flanch, and then you would put this whole thing in the vacuum tube that's inside the solid line. 203 00:32:14.780 --> 00:32:18.860 Mark Kushner: There's also variations that you can do on the basic non-neutral plasma trap 204 00:32:18.910 --> 00:32:23.780 Mark Kushner: where you have electrodes that start out, Nero, and they get wider and wider. 205 00:32:24.070 --> 00:32:26.900 Mark Kushner: and you deliberately put in some nitrogen gas. 206 00:32:27.150 --> 00:32:34.030 Mark Kushner: so that you get you use, but you pump it out on this size, so you have higher pressure in the skinny one 207 00:32:34.110 --> 00:32:38.220 Mark Kushner: somewhat lower pressure and the fatter one, and then the lowest pressure and the fattest one. 208 00:32:38.490 --> 00:32:44.290 Mark Kushner: And so you have a stepped pressure profile that you combine, combined with that potential profile. 209 00:32:44.750 --> 00:32:55.300 Mark Kushner: And this is a way to capture positrons from a low density DC. Beam. So if you didn't have the gas in here. these positrons would come in. 210 00:32:55.500 --> 00:32:59.540 Mark Kushner: bounce off the potential on the back here and go back out again. 211 00:32:59.670 --> 00:33:13.860 Mark Kushner: But they can excite an electric electronic excitation and the nitrogen gaps and lose energy. And then they get trapped and do this a couple of times. So you're you know you have, an input that's a DC. Beam. If you would close the gates 212 00:33:14.100 --> 00:33:16.650 Mark Kushner: you'd only trap one or 2 positrons at a time. 213 00:33:16.950 --> 00:33:25.290 Mark Kushner: but by by having this step potential and pressure profile you can collect your positrons into a cloud 214 00:33:25.320 --> 00:33:29.400 Mark Kushner: and then move them over into higher vacuum stages as a pulse. 215 00:33:29.650 --> 00:33:32.900 Mark Kushner: And so this is then 216 00:33:33.060 --> 00:33:47.660 Mark Kushner: one of those higher vacuum stages where you can have a nest, a a nest of traps that you can store positrons in a high magnetic field and a high vacuum to get increase. The total number of positrons you can get in one place at one time. 217 00:33:48.410 --> 00:33:53.020 Mark Kushner: and so the those are the the next 2 things in the green boxes up here. 218 00:33:53.660 --> 00:34:08.750 Mark Kushner: Once we have enough of the front. We want to combine them with electrons. And so then we need to move to the toroidal traps, and there we have 2 of these that we're developing. This one is being commissioned, and this one is still on the design phase 219 00:34:10.179 --> 00:34:18.100 Mark Kushner: and the one on the left you zoom in. There is a levitated dipole trap. So there you have a current carrying superconducting coil. 220 00:34:18.400 --> 00:34:21.190 Mark Kushner: but therefore creates a dipole magnetic field. 221 00:34:21.560 --> 00:34:26.210 Mark Kushner: and it's held up in your vacuum chamber by a much weaker 222 00:34:26.280 --> 00:34:28.480 Mark Kushner: feedback control lifting coil. 223 00:34:29.050 --> 00:34:42.199 Mark Kushner: And so you get closed field lines that your your charged particles can be on. And so all of your field field lines are purely to period, purely pollution, and the the dipole, and you have a continuous. 224 00:34:42.230 --> 00:34:43.960 Mark Kushner: a continuous symmetry. 225 00:34:45.469 --> 00:34:49.929 Mark Kushner: The other very good option for confining a pair. Plasma is accelerator. 226 00:34:50.560 --> 00:34:56.540 Mark Kushner: This is has much more complicated, many more coils. You need to have a 227 00:34:56.800 --> 00:35:00.220 Mark Kushner: a total field that also has a helical twist. 228 00:35:00.420 --> 00:35:16.360 Mark Kushner: so that One way of doing this is to have these toroidal field coils, and then these helical field coils, and that's kind of the classic way to make a celebrator. There are many different ways to make a celebrator some work better for trapping particles than others. 229 00:35:16.450 --> 00:35:19.180 Mark Kushner: But the basic idea is that you created a 230 00:35:19.440 --> 00:35:27.150 Mark Kushner: helically twisted magnetic field in in that that's closes for what we only using external coils. 231 00:35:29.290 --> 00:35:35.940 Mark Kushner: And why do we want to do both of these? Well, they're both steady state on the plasma timescales. 232 00:35:36.220 --> 00:35:50.660 Mark Kushner: They both the confine the charged particles without requiring any currents, because we'll have so few particles at such low densities that we can't generate magnetic field from the particles that are substantial. 233 00:35:51.010 --> 00:35:55.330 Mark Kushner: and both of these have been shown to be able to confine both 234 00:35:55.780 --> 00:36:10.750 Mark Kushner: non-neutral and quasi-neutral plasmas. So the this is a levitated dipole trap in Japan that has confined both cure, electron and and caus and neutral plasma. And this is a simple stellator at Columbia. That's done the same thing. 235 00:36:12.570 --> 00:36:13.590 Mark Kushner: and 236 00:36:13.960 --> 00:36:21.270 Mark Kushner: they have very different magnetic topologies. So each field line and the dipole goes around once invites its own tail. 237 00:36:21.800 --> 00:36:30.680 Mark Kushner: whereas a single field line and the accelerator on a on an irrational surface goes around infinitely many times, filling up the whole surface. 238 00:36:31.900 --> 00:36:47.800 Mark Kushner: And here you have truly political field lines. Here it's it's primarily toroid, but with a twist. and so you can expect to have significantly different a complementary plasma phenomenon going going on in these 2 types of confinement devices. 239 00:36:47.970 --> 00:37:01.870 Mark Kushner: and they also have complementary technical aspects. So we are fortunate that we have gotten funding to work on both of them, because it helps us to really multiply our diagnostics and our techniques to develop both. 240 00:37:02.610 --> 00:37:14.230 Mark Kushner: And so, finally, the last step was: once we have enough positron and the traps, and we put, and we we put those together with electrons. We want to study the transition from the regime 241 00:37:14.350 --> 00:37:25.250 Mark Kushner: of single particle behavior to the regime of collective polynomial behavior, to find out if our pair plasmas are stable to turbulence. 242 00:37:25.250 --> 00:37:34.880 Mark Kushner: what limits their confinement time, and how robust they are to fiddling with the symmetry like to creating temperature asymmetries, or to add even times and ions things like that. 243 00:37:36.430 --> 00:37:37.370 Mark Kushner: So 244 00:37:37.520 --> 00:37:53.410 Mark Kushner: how are we doing on it? So this gets to the part where we're looking at some of the parts in between, and the key questions, because some of the key questions had to do with these in between parts. The first one of them was, how are we going to get the positrons into our 245 00:37:53.410 --> 00:37:59.730 Mark Kushner: a magnetic field that does a good job of keeping particles in also tends to keep charged particles out. 246 00:38:00.890 --> 00:38:02.750 Mark Kushner: So in 247 00:38:02.860 --> 00:38:19.380 Mark Kushner: linear devices that trap antimatter, you like these penny mumber traps, you usually have magnetic field lines that you can send particles in up particles in on from a distance. So this is the case, for example, for the alpha traps shown here that collects anti protons 248 00:38:20.430 --> 00:38:25.110 Mark Kushner: for electron. I am Plasma is you? Usually ionize them already in your confinement device. 249 00:38:25.730 --> 00:38:31.280 Mark Kushner: And when you're doing electron experiments in a troll device like 250 00:38:31.320 --> 00:38:37.580 Mark Kushner: like in Rt one. Here you don't care how efficient you are putting in the electrons, because electrons are cheap. 251 00:38:38.830 --> 00:38:45.360 Mark Kushner: Lots of trends are not 10 to the 9 positrons per second is only a £160. 252 00:38:45.440 --> 00:38:56.390 Mark Kushner: And if you Google, most expensive substance, that will confirm, that that's anti-matter. So we want to be be very efficient with our precious positron and get them into the trap. Efficiently. 253 00:38:57.220 --> 00:39:06.720 Mark Kushner: Preliminary simulations had suggested that we could use ecosystem to do this to drift them across our field into our device. But these simulations were also very fiddly. 254 00:39:07.320 --> 00:39:21.540 Mark Kushner: and then, therefore, we needed to do experiments to establish the viability of drift injection. When we have a real world electron mean that has a a spatial spread and an energy spread. And this was the proof of principle set up 255 00:39:21.720 --> 00:39:24.460 Mark Kushner: that one of my colleagues built to do this. 256 00:39:24.590 --> 00:39:28.120 Mark Kushner: and involves a permanent magnet on a support. 257 00:39:28.560 --> 00:39:31.230 Mark Kushner: so i'm affectionately known as a magnetic. 258 00:39:32.240 --> 00:39:36.800 Mark Kushner: and we also didn't didn't have pulses of positrons yet. 259 00:39:36.840 --> 00:39:48.780 Mark Kushner: So this is what we were doing for several years in terms of trying to figure out these key questions. Instead of having these 5 boxes, we had 2 positron source and our magnanimistic. 260 00:39:48.970 --> 00:40:00.670 Mark Kushner: and it's amazing how much you can figure out with a magnetic field lines into our trap. 261 00:40:00.870 --> 00:40:03.540 Mark Kushner: and do that efficiently, so losslessly. 262 00:40:04.580 --> 00:40:12.090 Mark Kushner: And the way that that works looks like this. So you have your dipole magnet that's creating your magnetic field. 263 00:40:12.270 --> 00:40:23.630 Mark Kushner: The confined orbits are the ones like. When you run in plasma class about motion in a dipole magnetic field, you have your cyclicron orbit. You have your your mirroring, and then you have your toroidal drifts. 264 00:40:23.760 --> 00:40:33.490 Mark Kushner: And so that's the sort of the confined orbits. The positrons are coming from a beam line. In this case the beam line is off access, although ultimately it will be moved on access. 265 00:40:33.900 --> 00:40:48.250 Mark Kushner: So the positrons are coming in. If nothing happened, they would hit the top of the magnet, but by having them go between these plates that are oppositely biased, we create an electric field that's more or less perpendicular to the magnetic field. 266 00:40:48.370 --> 00:40:55.420 Mark Kushner: The electric field here is coming out of the board. The magnetic field is running along the field line, and then you get an E. Cross B drift 267 00:40:55.450 --> 00:40:59.950 Mark Kushner: that causes your positrons to direct across the magnetic field. 268 00:41:00.280 --> 00:41:14.310 Mark Kushner: They're still moving along the magnetic field toward the magnet until the magnetically mirror. Then they turn around, but now the drifted so much that they're heading toward the wall. They kick them back in again, and then they end up getting onto these confined orbits. 269 00:41:14.580 --> 00:41:21.760 Mark Kushner: and it turns out that with the real world positron being this, actually, you can do this and have the entire beam be injected into the trap 270 00:41:21.910 --> 00:41:26.670 Mark Kushner: as long as it's not too wide, specially, or 271 00:41:27.380 --> 00:41:34.320 Mark Kushner: or or in the velocity distribution. So we we have, but we have had lossless injection with the number Monk remoderated Beat 272 00:41:35.050 --> 00:41:44.260 Mark Kushner: once they get in there. This is what their orbit looks like. They'll go around. And then, as they approach back toward this injection region they'll hit the wall. 273 00:41:44.430 --> 00:41:52.110 Mark Kushner: This is a projection of the paths, the mid-plane crossings of the whole distribution function as they go around. 274 00:41:52.380 --> 00:41:54.470 Mark Kushner: and this is an example of a single orbit. 275 00:41:55.090 --> 00:42:06.580 Mark Kushner: But if you turn off the injection potentials, the ones that are in the trap at the time keep going around for hundreds of thousands of toilet transits. 276 00:42:07.270 --> 00:42:12.760 Mark Kushner: And so, if you look at the annihilation counts, they keep going for up to 10 s here. 277 00:42:12.990 --> 00:42:21.700 Mark Kushner: So it turns out that injecting with the Crosby drift, and then turning it off, allows you to trap them, and they they're on good orbits, and they're well confined. 278 00:42:22.170 --> 00:42:33.300 Mark Kushner: We've also done this when there was already a whole, there were already a whole bunch of electrons that were in the trap. So it works when there's a electron space charge already there 279 00:42:33.370 --> 00:42:35.860 Mark Kushner: doesn't work only in the single particle regime. 280 00:42:37.000 --> 00:42:50.260 Mark Kushner: and it also works. If you start off with higher depositrons, you can use a remoderator. So in this case a piece of silicon carbide turn them into lower energy positrons, and then drift, inject them. 281 00:42:50.770 --> 00:43:00.860 Mark Kushner: and if we end up having If our calculations show us that we can gain more by using higher energy positrons, we can turn them into low energy positron right where we need them. 282 00:43:02.820 --> 00:43:11.860 Mark Kushner: So there's the the glamour shot of our magnetonistic, a couple of field lines and an electron, and the positron going going going on there. They're trapped orbits. 283 00:43:13.660 --> 00:43:33.050 Mark Kushner: And this this continues to be a valuable sandbox. Now, it's being used for diagnostic development. These are a whole bunch of gamma diagnostics with a gamma source and some lines of response, and the magnet on the stick is in the background here for them experiments that were just conducted in Japan a couple of weeks ago. 284 00:43:33.050 --> 00:43:51.620 Mark Kushner: where the first positron pulses got injected into this trap. So, instead of having a few 100 positrons in there at once, we got up to between 10 to the 4 and 10 to 5 positrons in there once, which allows new diagnostic techniques for these things. So we're really excited about that. And the 285 00:43:51.620 --> 00:43:53.720 Mark Kushner: the work with the Japanese collaborators. 286 00:43:55.510 --> 00:44:05.360 Mark Kushner: So in terms of the Assembly and commissioning of new devices. So we've we're still using our magnetic, but we're ready to move on to our next filling in 287 00:44:05.510 --> 00:44:06.460 Mark Kushner: where you go. 288 00:44:10.710 --> 00:44:11.600 Mark Kushner: Hmm. 289 00:44:13.520 --> 00:44:21.230 Mark Kushner: Somehow I got a summary slide in there prematurely sorry about that. So there they are. So this is the 290 00:44:21.300 --> 00:44:27.240 Mark Kushner: these are the the green boxes. This was a system that was actually a floor model 291 00:44:27.330 --> 00:44:32.180 Mark Kushner: for about a decade. There was a company that sold positive, wrong beam systems. 292 00:44:32.200 --> 00:44:51.860 Mark Kushner: and then they decided to retire. Having sold positron beam systems around the world, they sold off their floor model. We got it, and it's been overhauled, and is now ready to go. Be installed in that experiment hall at the reactor that I showed you. It's been commesh commissioned with electrons by a master student very successfully. 293 00:44:52.110 --> 00:44:58.550 Mark Kushner: and and so it should be installed on the the reactor. Early next year 294 00:45:00.450 --> 00:45:18.540 Mark Kushner: the the multi cell trap that was this one from the diagram actually exists. There's the the wide cell. There are 3 off axis cells. Successful off access trapping has been achieved along with a whole bunch of other essential techniques for for getting this whole thing to work. 295 00:45:18.740 --> 00:45:22.520 Mark Kushner: This is work being done by the Phd. Student, Martin Singer. 296 00:45:22.520 --> 00:45:39.280 Mark Kushner: and we're hoping to move the multi cell track to within the next couple of years. So that'll allow us to go from. So the the trap on this page that I was talking about. This is the one with those stepped potential and pressure profiles that turns your DC. Beam into pulses. 297 00:45:39.280 --> 00:45:43.310 Mark Kushner: and you can get maybe up to like 10 to the 8, maybe 10 for 9, if we're lucky. 298 00:45:43.600 --> 00:45:49.830 Mark Kushner: And then this is where we're going to put all those pulses out of that system, so that we can get up to our 10, to the 10 or 10 to the 11. 299 00:45:51.710 --> 00:46:10.730 Mark Kushner: We also want to know what our equilibria look like for non neutral plasma and troll devices. So this is work being done by another Phd students. We're looking at the density and potential for pure electron plasma and the dipole geometry, since we might make a pure electron plasma and then put the positrons in. After that 300 00:46:12.810 --> 00:46:14.650 Mark Kushner: the levitated dipole trap. 301 00:46:14.950 --> 00:46:20.670 Mark Kushner: This is this is the CAD design, because you can see all what we're All the pieces are 302 00:46:21.340 --> 00:46:25.380 Mark Kushner: an important part of this was figuring out 303 00:46:25.430 --> 00:46:40.020 Mark Kushner: the engineering for getting this coil cool, and then getting the current induced in it, and then doing this repeatedly, because normally, when you want to pull something cryogenically, you clamp it down. 304 00:46:40.020 --> 00:46:57.440 Mark Kushner: But if you have a coil that you need to repeatedly cool, excite, Levitate, and then repeat this, and then it's going to be levitating and warming up, and then you have to repeat this process. You need to be able to cool something off repe repeatedly to to keep doing the experiment cycle. 305 00:46:57.760 --> 00:47:04.580 Mark Kushner: And and so Matt, Donking and Alex Card figured this out and 306 00:47:04.660 --> 00:47:08.610 Mark Kushner: designed and built, and are almost done with. Commissioning this device. 307 00:47:08.760 --> 00:47:16.620 Mark Kushner: It uses high temperature, superconducting coils from the a company that's a 20 min by bike, right away from IP. 308 00:47:17.880 --> 00:47:30.050 Mark Kushner: This is this is what it actually looks like. So this is that upper chamber here. It has a whole bunch of gamma diagnostics looking in. This is where you'll have the floating coil 309 00:47:30.140 --> 00:47:37.330 Mark Kushner: this. These are the injection for getting the positrons and the injection plates. And this is where you do the cooling cycles down here. 310 00:47:38.400 --> 00:47:45.460 Mark Kushner: This is what it looks like in person. So you a vacuum chamber, which is why I show the CAD diagram first, but it actually exists. 311 00:47:45.540 --> 00:47:52.800 Mark Kushner: and the this is one of the first. This is a photo of the coil in its case. 312 00:47:52.890 --> 00:47:58.450 Mark Kushner: This is one of the first induction tests. So to get the coil in there you first. 313 00:47:58.480 --> 00:48:04.140 Mark Kushner: you start off with coil with current in this charging coil. and you put the 314 00:48:04.250 --> 00:48:10.320 Mark Kushner: the coil. We call it the Floating Poly, and that's not floating. That's its name. You put the floating coil in the center 315 00:48:10.610 --> 00:48:21.340 Mark Kushner: while it's still warm, so it's not super conducting yet so it's in. It has a lot of magnetic flux through it. When it's not super conducting. Then you cool it out, so it becomes super conducting with magnetic flux inside. 316 00:48:21.680 --> 00:48:23.950 Mark Kushner: Then you turn off the charging foil. 317 00:48:24.130 --> 00:48:38.850 Mark Kushner: inducing the the current in the in the floating coil. Then you put the floating coil where you want it, and turn on the lifting oil to keep it where you want it to be in the middle of the chamber. So this is that induction process. So you see the 318 00:48:38.850 --> 00:48:45.600 Mark Kushner: initially, the magnetic field here is due to the the charging foil, which is the one you can see through the window here. 319 00:48:45.850 --> 00:48:57.490 Mark Kushner: and then you cool off the floating foil, so the temperatures in red. Then you do the infection, and you it traps all of the available flux, which was a very nice result that we didn't know we get. 320 00:48:57.650 --> 00:49:11.660 Mark Kushner: and then the natural decade time is on the order of a day, so this should be plenty of time to to do experiments. It'll decay faster when it's actually levitated and warming up. But this was a very nice result from last summer. 321 00:49:12.220 --> 00:49:17.150 Mark Kushner: So we're hoping to have it actually levitating very, very soon. This is: we have 322 00:49:17.230 --> 00:49:21.060 Mark Kushner: so for principal levitation movies that I can show you if you'd like. 323 00:49:22.350 --> 00:49:26.590 Mark Kushner: We're also designing a pair of plasma accelerator. This is the 324 00:49:26.690 --> 00:49:51.220 Mark Kushner: general concept. These are circular coils. They won't be circular, but the idea is to wind high temperature, superconductor on the 3D printed metal frame. Pull this, using a cold head in a simply connected vacuum chamber. You can. When you're doing electron positive from plasma, you don't have to worry about a lot of the same concerns as when you're making a fusion accelerator, which is very fortunate for us. 325 00:49:54.100 --> 00:50:03.980 Mark Kushner: as i'm low on time, I will not talk too much about the design, but if you're interested in accelerator design. I'm happy to to come back to this for for questions 326 00:50:05.360 --> 00:50:21.870 Mark Kushner: I already mentioned the need to be low aspect, ratio. We have some good low aspect ratio configurations that collaborators have have designed. And then we're working on some engineering tests to to figure out some of our inputs to to iterate with the design process. 327 00:50:23.160 --> 00:50:32.550 Mark Kushner: And now i'll go back to the summary slide that got disordered. Sorry about that. So in conclusion, laboratory per plasma. 328 00:50:32.660 --> 00:50:35.930 Mark Kushner: our compelling front here in fundamental plasma physics. 329 00:50:36.030 --> 00:50:52.580 Mark Kushner: We've made a great deal of progress in the last years on our plan to achieve these with the proof of principal setups to demonstrate things like injection and levitation and cooling of the the F Co. The floating coil for the located dipole trap. 330 00:50:52.680 --> 00:50:55.480 Mark Kushner: And now and and we've 331 00:50:55.740 --> 00:51:05.760 Mark Kushner: also gotten very far on the design, construction and commissioning of the the core experiments in the grand scheme with especially the 332 00:51:05.840 --> 00:51:13.800 Mark Kushner: this section, and this section being ready to go for next year, and then these 2, coming along a year or 2 later. 333 00:51:14.210 --> 00:51:15.640 Mark Kushner: the 334 00:51:15.770 --> 00:51:27.060 Mark Kushner: next few years are expected to be exciting, as we significantly improve our diagnostic capabilities. Trap orders of magnitude, more positrons and also electrons. And then install these on the react. 335 00:51:27.900 --> 00:51:29.140 Mark Kushner: Thank you very much. 336 00:51:34.260 --> 00:51:36.620 Mark Kushner: Oh, thank you other questions. 337 00:51:37.790 --> 00:51:38.890 Mark Kushner: Okay. 338 00:51:39.570 --> 00:51:46.000 Mark Kushner: I was wondering. You mentioned some diagnostics based on annihilation. But what other diagnostics are you all planning to use. 339 00:51:46.370 --> 00:52:03.470 Mark Kushner: So the because we might make a non-neutral plasma first. So make a pure electron plasma and then add positron to it. We can also use diagnostics on the walls that are used for non neutral plasma. So to start out with those and look for 340 00:52:03.470 --> 00:52:18.970 Mark Kushner: just seeing that the charge so the cold wall probes in general we can't stick anything into the plasma for any appreciable length of time, but so for the for the non for the intermediary non-neutral plasma wall probes 341 00:52:19.010 --> 00:52:25.640 Mark Kushner: for for doing some we might still be able for for doing measurements in the 342 00:52:26.290 --> 00:52:44.170 Mark Kushner: proto apex. The permanent magnet trap the magnet on the stick. We do stuff that stick probes into that when we, when we do electrons or when we're not worried about annihilating the positrons, we want to. We want to see where they went, but for actually doing the pair plasma. It'll be mainly gamma based. 343 00:52:44.170 --> 00:53:01.110 Mark Kushner: So there's a postdoc in the group ends Vander, London, who's been working on the gamma diagnostic development for the last 2 years, and he he was leading this. These experiments we just did in Japan, and there, because we have these different lost channels. 344 00:53:01.120 --> 00:53:02.900 Mark Kushner: you can potentially 345 00:53:02.970 --> 00:53:24.530 Mark Kushner: I you. You can put a bunch of detectors and see where the gammas are coming from, whether they're coming from the center or the walls, or the volume. If we got more expensive gamma detectors, then we might even be able to do some more sophisticated gamma spectroscopy. But one question is, how much that would bring us. So that's also something ends is working on 346 00:53:24.870 --> 00:53:33.490 Mark Kushner: if we need to do some additionally. Spatial resolved measurements. One thing we've thought about is developing like a 347 00:53:33.790 --> 00:53:34.940 Mark Kushner: like a pellet. 348 00:53:35.140 --> 00:53:51.640 Mark Kushner: like a plastic pellet system that shoots a p plastic pellet or through the the plasma. So you get then increased annihilation along its path, and then it it goes away, or to do like a fast, a a very fast colonated gas jet that would have the same sort of effect. 349 00:53:53.050 --> 00:53:57.090 Mark Kushner: But in general most of the diagnostics will be gamma based for the 350 00:53:58.720 --> 00:53:59.680 Mark Kushner: hey, Scott? 351 00:54:00.220 --> 00:54:05.990 Mark Kushner: Oh, could you come in? How the positron source from the reactor. 352 00:54:06.040 --> 00:54:08.680 Mark Kushner: I compare it to like a bit of a case source. 353 00:54:09.260 --> 00:54:18.300 Mark Kushner: And then, like a related question, are the different segments of the experiment? Like the accumulator. Are they like physically connected. 354 00:54:18.820 --> 00:54:26.740 Mark Kushner: perhaps, or like, accumulate, and then move the the actual, and it's somewhere else. 355 00:54:27.000 --> 00:54:29.360 Mark Kushner: So the I think 356 00:54:30.630 --> 00:54:34.310 Mark Kushner: I might have a on the slide about dated decay sources. 357 00:54:34.500 --> 00:54:42.210 Mark Kushner: but I probably have too many bonus slides, so so the slides so beta decay source 358 00:54:42.370 --> 00:54:51.760 Mark Kushner: as a very, very broad energy distribution. I'll just go back to the summary slide for this one. 359 00:54:51.930 --> 00:55:06.300 Mark Kushner: So be a beta decay course that energy distribution is really broad. You usually, if you want to so sodium. 22 is the most commonly used positron source in the world, and the way people usually use it is that they. 360 00:55:08.520 --> 00:55:25.110 Mark Kushner: if you want slow positrons. Then you might put it behind the tungsten foil, and then you lose the majority of your positrons in the tungsten. But the ones that come out, then have low energy, or you put it behind a layer of frozen neon 361 00:55:25.290 --> 00:55:31.950 Mark Kushner: and the same thing that that part of the velocity space gets enhanced, but the total number goes down. 362 00:55:32.600 --> 00:55:36.950 Mark Kushner: and so the reactor based source. 363 00:55:38.390 --> 00:55:44.230 Mark Kushner: So if you use the like sodium, 22, you can get 364 00:55:44.500 --> 00:55:53.640 Mark Kushner: with the new sodium 22 source that costs a €100,000 from South Africa, and has has a half-life of 2 and a half years. 365 00:55:53.730 --> 00:55:59.320 Mark Kushner: I think you can get into the 10 to the sixes, 10 to the £6 per second. 366 00:55:59.510 --> 00:56:03.160 Mark Kushner: and then obviously, it decays. 367 00:56:05.610 --> 00:56:06.810 Mark Kushner: and 368 00:56:08.650 --> 00:56:12.990 Mark Kushner: we we've talked about. I think there is a lot of 369 00:56:13.210 --> 00:56:19.600 Mark Kushner: room for development in positron sources and the scientific world. 370 00:56:19.790 --> 00:56:33.470 Mark Kushner: whether coming up with facilities that can create continuously like large amounts of data data plus emitters that then they could use to to fuel stronger beams. 371 00:56:33.490 --> 00:56:36.750 Mark Kushner: This is the a route that was suggested by 372 00:56:36.800 --> 00:56:44.110 Mark Kushner: Alan Mills that you see Riverside, who's like the grandfather of a lot of the positronium and and positron work. 373 00:56:45.320 --> 00:56:57.790 Mark Kushner: You could also do other reactor based sources. There's one in North Carolina that is, exists, but is underused. There are a lot of reactors that would could probably be used to make very good positive front sources. 374 00:56:58.260 --> 00:57:09.620 Mark Kushner: and you can also use Linux to create positrons. There are a couple of those. So so far. 375 00:57:10.010 --> 00:57:16.800 Mark Kushner: the Nepal nipple milk is the best source of full positron. I would love to see more development. 376 00:57:17.430 --> 00:57:23.100 Mark Kushner: either with larger amounts of beta emitters or lynx, based sources 377 00:57:23.240 --> 00:57:26.300 Mark Kushner: or other reactor based sources because it's 378 00:57:26.700 --> 00:57:33.100 Mark Kushner: we could use more positrons in the world. But but so far in it is the winner. 379 00:57:37.630 --> 00:57:55.310 Mark Kushner: Yes, yeah, about the posture and temperature. So you mentioned it's pushing one to 5. Ev. Is that coming from the source is always that something that you designed to heated out that's coming from these these traps. So the non-neutral plasma traps the 380 00:57:55.310 --> 00:58:01.080 Mark Kushner: in addition to having the nitrogen gas that allows you to trap the positrons in the first stage. 381 00:58:01.190 --> 00:58:17.760 Mark Kushner: The second stage usually uses a a cooling gas, because the magnetic field isn't strong enough to get cycle trunk pulling, but then the third stage with the nested traps, the magnetic field. The one we have is currently 3 Tesla, but we're aiming to have one that's at 5, Tesla. And then you get cycle trunk cooling. 382 00:58:17.940 --> 00:58:31.790 Mark Kushner: So these traps, the the pilotrons are typically cool down to sub ev scale, and then, when you transport them, you have to manipulate them, your pulses so that you don't create heating. 383 00:58:31.840 --> 00:58:38.470 Mark Kushner: So if we were being very optimistic. We would pull even lower temperatures, but we don't want to counter 384 00:58:38.490 --> 00:59:08.940 Mark Kushner: as it can temperatures before we measure them, so so that's why we're like Well, we. We don't want them to be too much hotter than one. Ev. Yeah, I I saw if you want a hot plasma that you seem that you want the code in. Well, actually, we want to cold one, I mean in principle, hypothetically. We could get to hold and have like in in an ideal world if we like. There, there is a lower limit to how cold we would want to be. Experimentally. We don't expect to reach that. 385 00:59:08.940 --> 00:59:16.840 Mark Kushner: So if we got to the point where, like our plasma, is too cold, and it's annihilating too fast. Then that's a very good place for us to be, because it means we have lots of the by. 386 00:59:20.550 --> 00:59:40.280 Mark Kushner: So you've mentioned that for your injection scheme. If you leave them on, then the positron will hit the wall, and that has some characteristic orbit time, so as presumably that limits your injection window. That is, that a strong linen, and why you're going to this for like multiplex 387 00:59:41.180 --> 00:59:43.120 Mark Kushner: trap injector. 388 00:59:43.290 --> 00:59:47.620 Mark Kushner: Yes, the short answer is, Yes, it is 389 00:59:48.770 --> 00:59:55.600 Mark Kushner: so. We have seen in simulations that there are some that Don't, When 390 00:59:55.760 --> 01:00:12.280 Mark Kushner: so, when we turn the injection potential back on again. So so when we do those confinement experiments where I show the positron staying in there for seconds, and we've turned off the potentials. And then we did, however long, and then we turn the potential back on again as a dump, so to to empty the trap 391 01:00:12.580 --> 01:00:15.830 Mark Kushner: and well, the I guys didn't. 392 01:00:15.890 --> 01:00:20.800 Mark Kushner: So we're simulating These discovered that when he did these there were 393 01:00:20.800 --> 01:00:41.880 Mark Kushner: maybe 5 of the positrons that weren't actually dumped, and it turns out that these were the ones that were near the plates when they were turned off. So they experienced breaking of their Adiabatic invariance and and and heating, and therefore they were dumped when the plates turn back on. So those actually have longer orbits, but they're hot, so we don't want them anyway. 394 01:00:42.200 --> 01:00:43.920 Mark Kushner: And so the 395 01:00:43.990 --> 01:00:53.840 Mark Kushner: and when we were doing these containment experiments, we would only because of these characteristic time window. It's like a 1010 microsecond, toroidal transit. 396 01:00:53.930 --> 01:01:01.810 Mark Kushner: And then you have like 5 times 10 to the 7 positrons coming in per second and going out per second. Then you end up with 397 01:01:01.830 --> 01:01:14.080 Mark Kushner: on the order of 500 and the trap at a time. But then that's why we want to go to these short pulses where the pulse might have a length of a 100 nanoseconds, so you can put in a pulse, and it'll spread out 398 01:01:14.120 --> 01:01:26.830 Mark Kushner: because you have a distribution of velocities, and then, when you open the door when you turn on the potential split in the next pulse you'll you'll lose a slice, but you put in many more at the same time. 399 01:01:26.920 --> 01:01:34.290 Mark Kushner: So that's that's the concept we're hoping to do pull stacking experiments in Japan next. But we didn't have time for them in the first theme time this year. 400 01:01:35.280 --> 01:01:51.280 Mark Kushner: and we would be doing more of these experiments in Germany. But the the reactor based source is currently doing a bunch of maintenance. So it hasn't actually been running since the pandemic. So we are really missing our and looking forward to getting them back again next year. 401 01:01:52.490 --> 01:01:59.110 Mark Kushner: Are you gonna be able to measure plasma waves and that kind of stuff. 402 01:01:59.660 --> 01:02:00.870 Mark Kushner: So 403 01:02:01.240 --> 01:02:19.380 Mark Kushner: so our our long hanging fruit is in terms of the confinement, times and and transport, and looking for any sort of oscillations with wall proves. So. Those are the first things we'll do is, how long does it first verify that we have densities and temperatures to call the plasma. 404 01:02:19.380 --> 01:02:27.260 Mark Kushner: Look at how long it lasts, and use Wall probes to see if we see any oscillations on the walls. 405 01:02:27.560 --> 01:02:31.470 Mark Kushner: The so, because 406 01:02:31.700 --> 01:02:45.530 Mark Kushner: we're we're in this very low density regime. especially like we. Basically, we we can't expect to see any sort of electromagnetic effects, because the we we can't make appreciable currents 407 01:02:45.600 --> 01:02:56.370 Mark Kushner: with our plasma that can compete with externally applied magnetic fields. So so there's there. There's a part of the parameter regime that we can look at 408 01:02:56.450 --> 01:03:03.730 Mark Kushner: what sort of like electrostatic waves we might be able to look at. We would need to look at in more detail 409 01:03:07.510 --> 01:03:12.000 Mark Kushner: No more questions and thank you very much. 410 01:03:22.740 --> 01:03:23.480 Okay. 411 01:03:23.630 --> 01:03:26.700 Mark Kushner: i'm. But on the top.