WEBVTT 00:00:41.000 --> 00:00:43.000 Thanks for having me here. 00:00:43.000 --> 00:00:55.000 I'm going to be talking about actually work that dates back to my PhD thesis many years ago, which wasn't on propulsion but was on plasma physics, and then I've. 00:00:55.000 --> 00:00:59.000 As I found in the course of doing that degree. 00:00:59.000 --> 00:01:11.000 I can't do plasma physics without trying to turn it into propulsion. So, that's how it ended up 00:01:11.000 --> 00:01:41.000 work. 00:01:41.000 --> 00:01:58.000 Okay, so what I'm going to be talking about is, it's a little bit of a generic title but I'll be narrowing it down to some specific physics, as we go and it's the physics impacts to plasma wave thruster design. 00:01:58.000 --> 00:02:17.000 What I say plasma ways, what I'm ultimately saying is that we're going to use waves that are usually often in the microwave or radio frequency RF thruster type of an application, and you're essentially beaming those fields into a plasma inside the chamber, 00:02:17.000 --> 00:02:25.000 using that to ionized, and at least ionized and produce and possibly accelerate the plasma. 00:02:25.000 --> 00:02:42.000 With these physics. The reason anybody would try and do this compared to the more DC thrusters that we've got in flight is that because they're electrode lists there's no exposed metal in a hot plasma with sputtering and such. 00:02:42.000 --> 00:02:44.000 there's a potential for long life. 00:02:44.000 --> 00:02:59.000 There's also because you get to, you can choose any material to contain the plasma as long as it lets the radio frequency and you could use potentially corrosive repellents for multiple different pellets in the same thruster, which is not traditionally 00:02:59.000 --> 00:03:06.000 something that you see in the ion thrusters and haul thrusters especially that we've been using mostly today. 00:03:06.000 --> 00:03:12.000 Those require specific specific charged a mouse. 00:03:12.000 --> 00:03:27.000 It's a quality neutral plasma from the, from the start, you don't have separate ions beams and then electron beams that have to recombine within using a neutral Iser, which is a system complexity advantage. 00:03:27.000 --> 00:03:37.000 There is a host of trust or concept using radio frequency no not necessarily using plasma waves. I tried to capture all of them here. 00:03:37.000 --> 00:03:45.000 There's inductive which is the base for there's a capacitive, which does still have exposed electronics with the grid. 00:03:45.000 --> 00:04:06.000 From trust me, the Universidad Carlos third of Madrid, as a Helikon source or near I has an ECR source, and also that's being tested here or a version of that being tested here at the university as I understand it, momentous has a microwave thermal thruster. 00:04:06.000 --> 00:04:23.000 And then there's of course there's the vas a mirror which is a Helikon wave, and ion cyclotron wave combined thruster that's being considered or proposed for higher power missions, 00:04:23.000 --> 00:04:38.000 share your screen because it's not only am I not. 00:04:38.000 --> 00:04:40.000 shared. 00:04:40.000 --> 00:04:48.000 I am screen sharing. 00:04:48.000 --> 00:04:59.000 I believe we've gone into presentation mode it stops. 00:04:59.000 --> 00:05:03.000 Let's try this. 00:05:03.000 --> 00:05:12.000 Oh my god. 00:05:12.000 --> 00:05:22.000 I'm not sure that I'm just there to share your screen as opposed to 00:05:22.000 --> 00:05:30.000 just trying to share the application. 00:05:30.000 --> 00:05:36.000 Let's try this again 00:05:36.000 --> 00:05:44.000 is that being sure, or am I, you 00:05:44.000 --> 00:05:50.000 not see it. 00:05:50.000 --> 00:05:54.000 Oh, 00:05:54.000 --> 00:05:57.000 you guys are seeing my. 00:05:57.000 --> 00:06:05.000 Let's see. 00:06:05.000 --> 00:06:13.000 Oh wait, there we go. All right. 00:06:13.000 --> 00:06:25.000 Okay, that says I'm screen sharing is I working. And if you want to go back to the full view. 00:06:25.000 --> 00:06:35.000 I know, it just 00:06:35.000 --> 00:06:44.000 on my computer 00:06:44.000 --> 00:06:57.000 work. 00:06:57.000 --> 00:07:22.000 Start getting a curses. 00:07:22.000 --> 00:07:30.000 How's that 00:07:30.000 --> 00:07:35.000 screen. Oh, now you're getting 00:07:35.000 --> 00:07:44.000 adjusted 00:07:44.000 --> 00:07:53.000 you swap your displays back and then you click New share. Now that you're in the Presenter View, you should probably be able to select the presentation style. 00:07:53.000 --> 00:07:59.000 Okay. 00:07:59.000 --> 00:08:10.000 Okay. Sorry about that. 00:08:10.000 --> 00:08:16.000 Okay, so what I'm talking about the physics aspects of RF wait thrusters. 00:08:16.000 --> 00:08:31.000 I'm going to speak from the standpoint of Helikon wave. So plasma source plasma thruster. This one, but it's still pretty generic as far as trying to get a wave into a plasma and use that, either for resources for for for propulsion. 00:08:31.000 --> 00:08:48.000 So, we have to consider when you're doing something like this, is that there's a way of coupling both which is the dispersion relation of the wave and we'll get into these things this is more than outline, and the antenna that you're using to the launcher 00:08:48.000 --> 00:09:07.000 radio waves, and the design and the shape of the antenna. And then you also have to worry about ionization and how are you, how is that RF fields are those RF fields, making the plasma that you're trying to get in source, there's various ways of getting 00:09:07.000 --> 00:09:19.000 that in terms of either collision, or collision less interactions between the electrons and the neutral gas to produce your ions and your electrons, and then you can. 00:09:19.000 --> 00:09:30.000 While it would be nice to have an unlimited knob for like density you know how much plasma you're making and you just turn up the knob for more power and you get more density. 00:09:30.000 --> 00:09:39.000 We're going to say that that's not that's not the case and that there's a physics that comes into limiting that as well. 00:09:39.000 --> 00:09:54.000 And so I'm going to talk a little bit about the thruster impacts from this way of coupling, and ionization issue. Some size stuff, and also this last little bit of something I've added on my own. 00:09:54.000 --> 00:10:10.000 After my thesis, which was on there's often referred to a double layer in a day you can see in some of these sources, where there's almost a it is a beam of ions coming out of it, just naturally. 00:10:10.000 --> 00:10:24.000 And there's a various ways that people have come up with to explain it, and this is going to be one aspect of where you can see this kind of a behavior based on the wave characteristics and the source characteristics. 00:10:24.000 --> 00:10:38.000 And it was something I realized that I could, could do, once I finished doing the analysis for the above the ionization and the wave coupling aspects of the Helikon source. 00:10:38.000 --> 00:10:57.000 You got plasma waves, for thrusters. I always like to say there's a whole Zoo waves that you can put in that exist in varying degrees for different magnetic fields very different frequencies, different densities, and I should add, and I kind of tried 00:10:57.000 --> 00:11:04.000 to be specific in the my initial slide not every radio frequency thruster is a plasma wave thruster. 00:11:04.000 --> 00:11:08.000 And in fact, I would. 00:11:08.000 --> 00:11:14.000 I guess it's a little catty to say that not every plasma wave thruster is a plasma wave thruster. 00:11:14.000 --> 00:11:22.000 So that sometimes the physics is not fully examine before they named it. So that's another thing to watch out for. 00:11:22.000 --> 00:11:25.000 So when you look at the helicopter wave. 00:11:25.000 --> 00:11:31.000 It's propagating in the an implied magnetic field is kind of a superficial description of it. 00:11:31.000 --> 00:11:48.000 It's the same regime as the Whistler waves in the Earth's upper atmosphere that we see on our radio signals after a lightning storm, what you've got is that you've got a frequency that's higher than the iron cyclotron frequency. 00:11:48.000 --> 00:12:00.000 And actually, then the higher lower higher than that I on the lower hybrid frequency and below the electron cyclotron frequency so you've got a specific rate range in which this kind of a wave exists. 00:12:00.000 --> 00:12:06.000 And if you go beyond those limits you're into another part of the zoo, and you're seeing a different kind of a wave. 00:12:06.000 --> 00:12:21.000 In this frequency range, because the frequency is much higher than how the than the, what the ions are moving at, you tend to, you're putting all your energy into the electrons, the electric in the magnetic fields from your radio frequency waves are going 00:12:21.000 --> 00:12:36.000 into the electrons and then that's being transferred from the electrons to the rest of the gas or to the ions. And the nice thing about this and also goes back to one of the advantages of an RF thruster is, if you're coupling to the electrons. 00:12:36.000 --> 00:12:45.000 Its species independent what you're putting in, you can still get these fields to energize the electrons and start up a plasma. 00:12:45.000 --> 00:12:49.000 If you were going to go do something that couples to the ions. 00:12:49.000 --> 00:13:04.000 For example, the part of the vas Amir thruster uses ion cyclotron heating which has a frequency that's tuned to a specific ion species. And if they decided they wanted to change the propellant that they were running through that thruster, they would either 00:13:04.000 --> 00:13:23.000 have to change their magnetic field or they'd have to change the frequency. So, so they change their mind halfway out into space or they've got an institute propellant they wanted to use, they would have to do some adjustments. 00:13:23.000 --> 00:13:26.000 So I'm going to call this a typical Helikon source. 00:13:26.000 --> 00:13:36.000 These have shown up in a lot of universities, none of them were trying to make them into a thruster that's why I call it a source. 00:13:36.000 --> 00:13:49.000 And they usually tend to be about the same size, same dimensions work about the same. This is the one, this is the diagram of the one 00:13:49.000 --> 00:13:53.000 I guess maybe if I use me, please my cursor. Yes. All right. 00:13:53.000 --> 00:14:10.000 The one I used in my, my thesis research. What it is is it was a 10 centimeter diameter quartz to, it was about two meters long as this two. And in this instance, I've got two antennas that were wrapped around the outside of the tube and that's where 00:14:10.000 --> 00:14:17.000 the radio frequency energy was was being developed. It will see a little bit more about the design of those antennas and a little bit. 00:14:17.000 --> 00:14:20.000 This to was filled with argon gas. 00:14:20.000 --> 00:14:28.000 There was some diagnostics that were used to try and measure plasma characteristics there's an applied field from these coils out here. 00:14:28.000 --> 00:14:45.000 It was typically on the order of about a 10th of a Tesla. 00:14:45.000 --> 00:15:05.000 But generally, The the typical part is that there is an antenna on a to about two meters long, about this transverse dimension, and then gas filling it and then you inject your RF waves in try and get a plasma. 00:15:05.000 --> 00:15:20.000 I would say that I've always kind of said the that kind of a Helikon source was almost like the Bic lighter of plasma sources, is that it was fairly easily constructed, and usually would turn on. 00:15:20.000 --> 00:15:26.000 And you could get a plasma. That was another reason for its popularity. 00:15:26.000 --> 00:15:35.000 So we air is the for my experiment, this would be allowed to, we would run this steady state continuously sometimes two hours. 00:15:35.000 --> 00:15:43.000 We'd have five to 30 militarism based pressure which is as much high as we could go for our pumping system. 00:15:43.000 --> 00:15:48.000 We could go to up to 800 watts of RF power steady state. 00:15:48.000 --> 00:16:04.000 And then I also have that separate separate power supply to do a shorter pulse at 123 kilowatts of power. And this is this the whole genesis of this way, which I'll go into a little bit as this whole trying to get. 00:16:04.000 --> 00:16:09.000 See if I can turn a knob and get more density out of a plasma source. 00:16:09.000 --> 00:16:13.000 It turns out, you can't that way. 00:16:13.000 --> 00:16:16.000 So uniform axial magnetic field. 00:16:16.000 --> 00:16:26.000 We looked at multiple intended it but the two that ended ended up being used are these two that are, are shown in this is a finger on the side. 00:16:26.000 --> 00:16:45.000 We looked at density with langur probes and interferometer did some magnetic field probing to measure the wave fields in there and monitor the neutral pressure in the discharge with a capacitive phenomena or during operation. 00:16:45.000 --> 00:16:56.000 Not all this has to do with the thruster parts I'll try and go through it but this is just some ideas of some of the measurements, these are radial profiles with density and temperature and the source. 00:16:56.000 --> 00:17:15.000 So temperature about three or four EV densities, up to tend to the 19th per cubic meter, which is considered high for for your average, average lab source and another reason why these are very popular for experiments. 00:17:15.000 --> 00:17:19.000 And this is just an example of what would happen. 00:17:19.000 --> 00:17:30.000 As I said if you tried to turn that knob of power and get more density out of the discharge and you can see we're going going up and up in power here and this is a steady state measurement. 00:17:30.000 --> 00:17:38.000 And the density reaches an asymptote, have a maximum of how high it could be a no matter how much more power I'm putting in. 00:17:38.000 --> 00:17:46.000 I, it's not going into creating ions and electrons. 00:17:46.000 --> 00:17:53.000 Correspondingly, what happens is when I'm running steady state and I turned on the power. 00:17:53.000 --> 00:18:00.000 And then they look at the pressure in that, in that chamber. And this is the pressure at the edge of the chamber. 00:18:00.000 --> 00:18:21.000 You can see that the pressure starts off at one, it's normalized. And regardless, even at moderate powers, it drops to about 10% of its of its original value, while the plasma is on especially at the center of the discharge. 00:18:21.000 --> 00:18:26.000 So this was this was the observation here is that the density doesn't increase with power. 00:18:26.000 --> 00:18:31.000 I don't show it here but some antennas that we use work better than others. 00:18:31.000 --> 00:18:47.000 There's lots of people who've worked out why for that as well, there's a strong decrease in neutral pressure during the plasma operation. And the question is, is how does this start affecting the trusted source and and thruster design. 00:18:47.000 --> 00:19:00.000 So the first thing from the original outline is that they're one of the issues for plasma wave is the coupling and the generation, and that all comes out through the dispersion relation. 00:19:00.000 --> 00:19:18.000 And I'm not going to go through all of these equations, but it's it's a bit suffice to say you do the equations emotion. 00:19:18.000 --> 00:19:23.000 your wavelength, or in this case, just to make sure. 00:19:23.000 --> 00:19:34.000 I'm not over, assuming usually where I've been. I'll be talking to the wavelength parameter that I'll use is this k number which is actually an inverse wavelength to pi over lambda. 00:19:34.000 --> 00:19:43.000 So the frequency the wavelength, the density of the plasma, the applied field strength in the plasma. 00:19:43.000 --> 00:19:57.000 Ah, yeah and that's it so. So that's, you know, you do the basic physics and you report workout this this dispersion relation and the solution of that is going to vary and give you different wavelengths a different frequency ranges, depending on what 00:19:57.000 --> 00:20:14.000 kind of densities you're putting in what kind of magnetic fields. So even in this, this is a general relation but out of this you get a dispersion relation for certain frequencies for a Helikon wave. 00:20:14.000 --> 00:20:22.000 And this is, this is where you start getting into what does your basically your antenna have to look like, or your source. 00:20:22.000 --> 00:20:40.000 And what I did is I took that dispersion relation which is a fairly involved derivation. I have to that, that k number is actually a vector. So I have two directions, I have a parallel wavelength and perpendicular wavelength. 00:20:40.000 --> 00:20:57.000 I solve her for both of those as a function of density and in this case this delta parameter that you see here is the frequency divided by the electron cyclotron frequency so range of frequencies, and I got these contours. 00:20:57.000 --> 00:20:59.000 In, 00:20:59.000 --> 00:21:07.000 were worth worth how what the where the wave for these different frequencies is appearing in terms of density. 00:21:07.000 --> 00:21:17.000 And this this wavelength. And you can see that if I for this frequency for as an example of a very low frequency. 00:21:17.000 --> 00:21:30.000 I have to have a low kz number, so a, which means a high axial wavelength. If I want to get. 00:21:30.000 --> 00:21:48.000 If I want to get densities here for this frequency that's what this is telling me I, and I actually have two choices of two types of debt to degree values of density that I can see here, which is depending which either one is possible in the, in the discharge. 00:21:48.000 --> 00:21:55.000 So it's, it's not an easy. The dispersion is not easy and you end up with, with multiple solutions. 00:21:55.000 --> 00:22:10.000 And this just kind of narrows down what you can expect, or for your, your source to design or where you need to be in your source to get a certain density, if you will, or to cut you know to get good coupling. 00:22:10.000 --> 00:22:22.000 And this is enough just another way of saying this is this is this is wavelength with density contours for different frequencies, but it's the it's the same idea. 00:22:22.000 --> 00:22:35.000 This isn't necessarily considered right away when somebody builds one of these sources, it gets very, very important if you're going to try and build a thruster and you're saying, Oh my thruster is going to be this big. 00:22:35.000 --> 00:22:52.000 In that drives you into a regime on these, these devices that tends to be either kind of unrealistically high densities, or just that you're never going to actually be able to generate that wave in that source, especially in a small source. 00:22:52.000 --> 00:23:01.000 I also don't talk about that here but we did try once building a small source. 00:23:01.000 --> 00:23:13.000 We could get plasma we could not get the plasma that would equate to having a Helikon wave in it. I mean, it wouldn't match it. There was no, no way of going through it. 00:23:13.000 --> 00:23:18.000 We were just using electric and magnetic fields to inductive lead generator. 00:23:18.000 --> 00:23:31.000 And when we tried to get it to work up to where we needed it to go for the Helikon density that would meet the dispersion and make the whole system work. 00:23:31.000 --> 00:23:35.000 The antenna melted. 00:23:35.000 --> 00:23:43.000 Because Because until you can couple that way the more energy is going into circulating in the antenna than it is going into circulating into the plasma. 00:23:43.000 --> 00:23:58.000 And that's, that's the difficulty you're running into and that's this this kind of relationship is will give you the idea that's why you're either explain to you why you're intending was melting, or tell you how you need to build the source that will 00:23:58.000 --> 00:24:15.000 make it a little easier to do that. And this is another part of the, of the issue is the antennas have wavelengths that they are naturally tend to select and it's actually related to their life. 00:24:15.000 --> 00:24:21.000 Okay. And this is an example for, I think it's this antenna. 00:24:21.000 --> 00:24:26.000 And it's two different lengths so this one is for a longer antenna. 00:24:26.000 --> 00:24:48.000 18 centimeters long. And this is the, the vacuums frequencies, the spectrum spectrum of K numbers are wavelengths that the the antenna is radiating at a higher fields. 00:24:48.000 --> 00:24:58.000 giving away all the next things. So right like so add a cake here of kz of about 20. 00:24:58.000 --> 00:25:10.000 You're getting the highest feels the highest power from this antenna that it can put out and then that's going to drop off as you as you try and have it go, shorter and shorter. 00:25:10.000 --> 00:25:12.000 And then you can you can see here. 00:25:12.000 --> 00:25:17.000 If I get out. If I get out here 00:25:17.000 --> 00:25:30.000 for this, for, for a much higher kz which actually from the last slide, I guess. Let's see 00:25:30.000 --> 00:25:41.000 if I want to get to higher density here you can see I'm seeing that I probably need to get to very much higher Casey's can it be able to even be able to have the way if exist. 00:25:41.000 --> 00:26:01.000 And then, so you get to hear and so I try and get to a higher kz. This has dropped off quite dramatically. And then I look at a shorter antenna in here, it's not really coupling very well at this at this low kz which is a high wavelength, but it's actually 00:26:01.000 --> 00:26:11.000 doing a little bit better than the than the longer antenna when you try and drive to a higher density. So what that translates to is, there's two things, two things that could be going on and the sources. 00:26:11.000 --> 00:26:16.000 One is, is, you say oh I want to get more density, and I've got this antenna. 00:26:16.000 --> 00:26:27.000 And I turn up the power will I get up to the point where the density is driving me out here. 00:26:27.000 --> 00:26:44.000 And this antenna just is not putting in out any fields in that, in that at that link that that wavelength so there's the waves are just not the plasma is not seeing any inducement to be excited and have a wave at the at the at the right at that density 00:26:44.000 --> 00:26:53.000 so your your your antennas kind of selecting your maximum density in that regard. The other part 00:26:53.000 --> 00:26:57.000 is that as I go up and power. 00:26:57.000 --> 00:27:10.000 I'm losing neutrals. And I keep losing neutrals. And so that it ended up this is my thesis is which, which ends up being my really limiting cases that I'm running out of dense, I can't generate density because my antenna doesn't couple very well. 00:27:10.000 --> 00:27:14.000 Or am I running out of density because I've run out of neutrals. 00:27:14.000 --> 00:27:21.000 Of course, probably a little both, but 00:27:21.000 --> 00:27:28.000 this is another aspect of it, of the whole physics of these things. 00:27:28.000 --> 00:27:36.000 And that is, is, is how are you ionizing the plasma once you are getting the right frequencies and presumably the right wavelength. 00:27:36.000 --> 00:27:47.000 And there's there's several possible things that can happen in a plasma like this and the RF plasma, you get these get it started. 00:27:47.000 --> 00:28:04.000 The obvious one and the simple one, is that, just the electrons are all bumping against each other and they're bumping against neutrals and ions and they just collision Lee rxR ionizing more and more propellant or or gas, and you can you keep getting 00:28:04.000 --> 00:28:06.000 more density that way. 00:28:06.000 --> 00:28:20.000 The problem is is especially at some of the regimes where the Helikon is running at a pretty, pretty good density, these, it's still not high enough that these collisions would get give you the heating that you need. 00:28:20.000 --> 00:28:23.000 And you wouldn't keep making plasma. 00:28:23.000 --> 00:28:29.000 So there's another idea, which is, which I'm calling a collision less ionization. 00:28:29.000 --> 00:28:48.000 This is there's two very versions of this there's the easy version, which is a version of land out damping. And then there's the more difficult one where it's a Neil near field coupling of the way fields to two electrons and the plasma, but the, the main 00:28:48.000 --> 00:29:05.000 point I'm trying to get across is if you look here. The process for either of these two work has been that the way if you're going along at a at a face speed so you've got this electric and magnetic fields going along in the face speed. 00:29:05.000 --> 00:29:20.000 If there's an electron that happens to be going on, near that phase speed and they see this field when they see that field longer, and it works on that electron and get that one going up to the same speed as the wave. 00:29:20.000 --> 00:29:32.000 And you essentially get like beams of electrons. Okay. And it turns out this is why people like Helikon sources, is that the phase velocity for like that long antenna. 00:29:32.000 --> 00:29:51.000 With 13.56 megahertz is right where electrons, like to ionized neutrals. They're going just the right speed is the peak of the cross section, and you'll get the most ionization, and that is why people like the Helikon discharge, but that is a collision 00:29:51.000 --> 00:30:05.000 plus effect. And that doesn't necessarily always apply, and we're going to see that as I go through some of this analysis. 00:30:05.000 --> 00:30:21.000 And I say the Near Field effects. The differences the Lando is this gradual, the wave just keeps going and accelerating accelerating and the near field is is that the waves right near the antenna like scoop up a bucket full of the right electrons and 00:30:21.000 --> 00:30:39.000 just throw them out in bursts, and those all start ionizing something very effectively. But again, it depends on strongly on wavelengths. Okay and fake through the face speed of the wave, compared to the energy of the electrons. 00:30:39.000 --> 00:30:58.000 So, that is that is important, then that's where whites, the where the antenna has the highest field is so important, in turn, trying to do that to a Helikon source that will be effective for an application like a thruster. 00:30:58.000 --> 00:31:02.000 So, for the dispersion relation. 00:31:02.000 --> 00:31:21.000 We are getting that to increase the density I have to decrease the wavelength or the wavelength of the Helikon wave at a higher density than what we've seen is shorter than it is at the, at the steady state densities we've achieved the ionization process 00:31:21.000 --> 00:31:37.000 is that it, there's a wavelength dependence for the most part, and that they also can be a limit based on losing neutrals because you just ionized as many as you can and you run out of run out of gas, but a yes run out of gas. 00:31:37.000 --> 00:31:40.000 So I tried to examine those both effects. 00:31:40.000 --> 00:31:57.000 So what I did is I had that experiment that I had the diagram two antennas one short one long. Start the plasma with the long antenna at a relatively low power, and then juice the antenna with a pulse from the shorter antenna at a much higher power, and 00:31:57.000 --> 00:31:59.000 I did a range of powers. 00:31:59.000 --> 00:32:21.000 So now I have the neutral pumping going on, the whole time. And then I have the fact that I changed the magnetic or the wavelength of one of the antennas and trying to get to try and get to a couple to a higher density that way. 00:32:21.000 --> 00:32:30.000 And this is an example of the forward power. Total forward power when I was running the experiment. This was my steady state power all the way through. 00:32:30.000 --> 00:32:42.000 And that was still going. Even here, I guess I'm cheating with people on on zoom, I do that. 00:32:42.000 --> 00:32:53.000 So this is the steady state power here, and then this was a pulse, it was about 50 milliseconds, in the middle of the discharge 00:32:53.000 --> 00:33:00.000 sure that that's there. But anyway, 00:33:00.000 --> 00:33:07.000 and I won't go through in detail but this is a different powers and pressures. 00:33:07.000 --> 00:33:19.000 And the interesting things I was going to point out is at low pressures and low densities, I kind of don't get much 00:33:19.000 --> 00:33:34.000 right here this is increasing power this is constant power but increasing pressure but it low pressure is I don't even see much of an effect at a high pressures, I do see an effect, but it doesn't stay. 00:33:34.000 --> 00:33:40.000 And then here's at the very highest case and I see the effect twice. 00:33:40.000 --> 00:33:49.000 Okay, and then it drops down and then when this power turns off, there's this, this way down way drop down here because at this point this is just the steady state power. 00:33:49.000 --> 00:33:52.000 And then I recover back up to where I was. 00:33:52.000 --> 00:34:03.000 So I that in that we see the answers to both questions in that. 00:34:03.000 --> 00:34:13.000 Ultimately, the neutral pumping the neutral depletion is the dominant thing you have to worry about psych yes i satisfied. 00:34:13.000 --> 00:34:24.000 Yes I satisfy the dispersion here for a little while, But all that does all that increase in density does is take more neutrals out of the picture. 00:34:24.000 --> 00:34:32.000 That plasma can't keep up the neutral pressure starts drop there there the plasma density starts dropping again. 00:34:32.000 --> 00:34:36.000 And in fact, if I turn it off then. I lose. 00:34:36.000 --> 00:34:45.000 It's so much less neutrals, then the steady state that the steady state needs to wait for everything to fill in, before it can recover. 00:34:45.000 --> 00:34:52.000 So that's so that's two issues. So, the wavelength does matter, 00:34:52.000 --> 00:35:11.000 but not at all conditions. And, I think, like, interestingly, at a at a low pressure. I'm not seeing as much. I'm not even saying that I get a low pressure which is also a lower density I don't see anything from the pulse as well so that's, that's an 00:35:11.000 --> 00:35:31.000 interesting effect to that, the way the wavelength didn't get the short, short antenna is probably not even coupling at the lower densities. And then the one anecdotal, part of that is if I tried to start the plasma with that short antenna alone. 00:35:31.000 --> 00:35:36.000 They won't start where it certainly won't get to Helikon way, it just barely starts. 00:35:36.000 --> 00:35:56.000 And this has been seen this was seen in the early days of Helikon sources everybody was changing the field so that they made their antenna too short. They couldn't even get to that to that regime, which is why I knew I had to go to. 00:35:56.000 --> 00:36:08.000 So, the higher power pulses, we do get density, but it decays really quickly, but you could argue that that that's where the wavelength is mattering. 00:36:08.000 --> 00:36:14.000 But the neutral pressure is also has a higher neutral pressure has a greater effect. 00:36:14.000 --> 00:36:18.000 In terms of what your density is going to be. 00:36:18.000 --> 00:36:25.000 And then so then I this frankly, in a way, I hate to break this too, but this was all kind of background. 00:36:25.000 --> 00:36:37.000 This all the data that went into coming up with a model that tried to look at this and it's in what I wanted to get at is that it's a particle balance model and an energy balance model. 00:36:37.000 --> 00:36:42.000 And there's theories that say, how the 00:36:42.000 --> 00:36:49.000 how well they take into account that nonlinear the land out damping wavelength dependent coupling. 00:36:49.000 --> 00:37:08.000 And I included that as one particular way of depositing energy in the plasma, and I included just the regular old conditional way. so I had these two competing processes, and I included multiple levels of ionization in the discharge, which we won't get 00:37:08.000 --> 00:37:09.000 into. 00:37:09.000 --> 00:37:14.000 But so all of those effects were incorporated into the model. 00:37:14.000 --> 00:37:15.000 Just like real life. 00:37:15.000 --> 00:37:28.000 And I won't get into this too much more this is just some cross sections that were used, same server forward power model or input into the model that I got from the experiment. 00:37:28.000 --> 00:37:48.000 And again, this was like a zero D got a tube of plasma of a certain diameter, which we measured from those radio profiles. And then I ran it with that and track the neutrals the electrons and the electron temperature in the discharge. 00:37:48.000 --> 00:38:01.000 And so this was the result of some sample results, and I get similar similar behavior as to what we see in the experiment I don't quite get that. 00:38:01.000 --> 00:38:03.000 Second. 00:38:03.000 --> 00:38:18.000 Second peak here. If I go to a higher pressure than what I actually ran at I do, I can get that so this models not exactly correct in the magnitudes. But the trends are about the same. 00:38:18.000 --> 00:38:22.000 And you see that there's very little effect. 00:38:22.000 --> 00:38:27.000 Front at low, you see her, don't see much change at the low powers. 00:38:27.000 --> 00:38:35.000 So this is with power increasing and then you do, you do see that you, you do get a benefit even though it might drop off later. 00:38:35.000 --> 00:38:39.000 And then, this was with pressure increasing. 00:38:39.000 --> 00:38:44.000 And again, same same sort of behavior. 00:38:44.000 --> 00:38:50.000 You can see that, and you can see the neutrals get sucked down quite a bit. 00:38:50.000 --> 00:39:06.000 When I'm when I'm doing a pulse, even at the high pressure and that's why is certainly experimentally you had that recovery I don't have quite that much of an issue here in the model but it's very close in predicting it. 00:39:06.000 --> 00:39:11.000 And when we end. 00:39:11.000 --> 00:39:17.000 Oh, good. All right, I might have questions 00:39:17.000 --> 00:39:26.000 that lead me to another idea, which has to go back, which goes directly to the thrusters 00:39:26.000 --> 00:39:37.000 is that I'm modeling this nonlinear wavelength dependent trapping mechanism. And I'm modeling the whole dis discharged as a whole. 00:39:37.000 --> 00:39:46.000 And there's, there's been, there's been to ongoing debates in these in these sources. 00:39:46.000 --> 00:40:05.000 One is, when they first proposed the land out damping idea and coupling to just electrons and getting beams. Everybody went looking for them, and they're very hard, it's hard to see something like that because it's at a RF frequency, especially the bursts. 00:40:05.000 --> 00:40:21.000 And if you're just probing a language probe in an RF plasma it's picking up all of the RF waves. Anyway, and to see to see some bursts of electrons or little beams of electrons, along with that. 00:40:21.000 --> 00:40:38.000 It just keeps getting swamped down, and then if you shield it out the RF noise you shield it out the beams because they were still at sit there modulating the same frequency, so it was one of those inferred but not really dead identified. 00:40:38.000 --> 00:40:53.000 And the other ongoing debate is having what's called a double layer having a standing potential drop out of the out of the discharge. 00:40:53.000 --> 00:41:04.000 There's been a couple of reasons that could be either the, the old thruster ideas that you have an expanding magnetic field and that gives you a drop and accelerate stuff out. 00:41:04.000 --> 00:41:20.000 And, but then the other, the other question I had is well what if you did have a be of electrons as a phase away face velocity. And that's just going out of this discharge regardless of an expanding field or in with that's leaving your discharge has a 00:41:20.000 --> 00:41:41.000 current, and you want to have an MP polar plasma where there's no net change in charge so you're going to have to have something that counters this high energy beam of current coming out of the plasma and I realized this model calculates those beams. 00:41:41.000 --> 00:41:56.000 So why so now this is the this is the new part. So this is where I said well why don't I use that model, see if I can calculate how much that trapped current is which I don't do in the overall particle balance and see if I can estimate what kind of potential 00:41:56.000 --> 00:42:11.000 potential drop I could get in where I can get it in the clouds. And again this goes to. There have been Helikon double layer thrusters proposed and tested the varying degrees of success. 00:42:11.000 --> 00:42:23.000 And this would be an impact on how would you know where, where you should be designing a thruster like that if that's the the effect you're trying to get. 00:42:23.000 --> 00:42:47.000 So, I've got a high energy beam of one species and that's determined by the model. And by this, this trapping analysis that takes into account the Lando damping interaction and ionization in the in the discharge, it takes into account, heating and such. 00:42:47.000 --> 00:42:58.000 I'm not doing the pulsing in, or anything this is just a discharge, but I'm creating these beams, and then thing I should I realize they really need to be specific about. 00:42:58.000 --> 00:43:08.000 There's no expanding magnetic field in this analysis okay so I'm not looking at what if it expands I got another paper that does that. But that's not what I'm talking about. 00:43:08.000 --> 00:43:23.000 So this is just literally a two, with no change in the magnetic field at the ends, but you've got a Helikon way of going through it, and it's it's grabbing these electrons in shooting them out when it okay and then what does, what does that do to the 00:43:23.000 --> 00:43:25.000 overall. 00:43:25.000 --> 00:43:38.000 And the polarity of the, of the plasma and whole and can you see some sort of a potential drop and acceleration. As a result of that. 00:43:38.000 --> 00:43:41.000 So, 00:43:41.000 --> 00:43:53.000 this, this was my one of my first cases, it's a low field, and a low pressure. Okay and then I run the model. And I looked at what I'm showing here is here's the. 00:43:53.000 --> 00:44:02.000 The Andy polar potential that arises from the in the discharge from from these conditions with whatever being gets produced. 00:44:02.000 --> 00:44:07.000 It's a very low density discharge. 00:44:07.000 --> 00:44:15.000 I get about 90 volts. And people are potential. That's not bad. I mean, you can. 00:44:15.000 --> 00:44:29.000 People have been trying to do measurements of that and usually it's multiple, you can argue that you get multiples of an electron temperature, this is probably higher than the than the multiple of the electron temperature and the most interesting thing 00:44:29.000 --> 00:44:41.000 is, I got an Amy Poehler potential, what do I have I have two different currents here one is the trapped current that's getting shot out as a beam from the RF coupling. 00:44:41.000 --> 00:45:03.000 And the other blue is the what I'm calling just the bone current of, you know, ions drifting out of the out of the end of the two. Okay. And those are those are the two that if it was a normal plasma, with two Maxwell Ian's you that your bomb speed and 00:45:03.000 --> 00:45:21.000 your electrons that currents would cancel you would be, you would have net neutral, neutral carbon. 00:45:21.000 --> 00:45:33.000 shot out the back. And that is where this this potential arises, and that's going to accelerate the if is trying to accelerate the ions out past past boom speed. 00:45:33.000 --> 00:45:47.000 And so, so this is telling me Yeah, they're running low pressure and low field. I should I could possibly be getting this beam and I could possibly getting be getting acceleration out of the out of my thruster, and again without an expanding magnetic 00:45:47.000 --> 00:45:55.000 this is Apart from that, this is low pressure and high field. And I'm not seeing that. 00:45:55.000 --> 00:46:01.000 Okay, I get three tenths of a volt so basically nothing, I've got a high density. 00:46:01.000 --> 00:46:10.000 There's almost no traps. So, what that's telling me is, is my high field 00:46:10.000 --> 00:46:31.000 is taking me away from where the phase velocity and the electrons are interacting, well enough to get me a beam, and that is primarily a conditional plasma, and I'm just getting regular bone speeds, and stuff out of the out of the discharge. 00:46:31.000 --> 00:46:36.000 So it's a low field and high pressure. 00:46:36.000 --> 00:46:43.000 I get a moderate moderate potential drop moderate densities. 00:46:43.000 --> 00:46:46.000 And, but I'm still getting. 00:46:46.000 --> 00:47:06.000 I'm getting traffic particles that are are exceeding the bomb speed, which is, again, which is echoed in the MB polar. So, this is, this is two cases with low field where I'm seeing that I could be getting up and be polar potential and potential acceleration, 00:47:06.000 --> 00:47:09.000 one case where I don't. 00:47:09.000 --> 00:47:12.000 And then high pressure and high field. 00:47:12.000 --> 00:47:18.000 Also, it's, you're getting, I got nothing. 00:47:18.000 --> 00:47:34.000 No trapping, this is all conditional in the in the power balance. And so everything is just leaking out the normal way of plasma would leak out with net zero current. 00:47:34.000 --> 00:47:47.000 So, what we're getting at is that it's tending to be if you want to try and get this kind of an acceleration in your thruster or scores. You probably need to go to low field probably low density. 00:47:47.000 --> 00:47:59.000 This is going to be driving that collision lyst wave coupling which gets you your beam, as opposed to the usual cool on collision things with as has no beams it's just all isotopic. 00:47:59.000 --> 00:48:14.000 And the other part of this is that if when you're trying to get this collision this wave coupling. It's also going to, you also have to make sure that you're getting your wavelength right of the antenna to be compelling to them, to the right face, need 00:48:14.000 --> 00:48:20.000 to be able to get that name. 00:48:20.000 --> 00:48:40.000 So, My implications here for the wave based sources and are certainly the Helikon lines is density is limited most strongly by neutral depletion have to take that into consideration there have been people trying to address that, with like supersonic neutral 00:48:40.000 --> 00:48:49.000 injection and down the middle of the chamber and such. And I actually haven't seen too much of that succeed. 00:48:49.000 --> 00:48:51.000 If you were. 00:48:51.000 --> 00:49:06.000 I haven't talked to them but if you were at Astro with your resume your source, and you were worried about the density in your increasing the density and your Helikon source which is person stage of their, their device. 00:49:06.000 --> 00:49:14.000 This would be where they would have to look right now I think it's rear injection into the back of the plasma. 00:49:14.000 --> 00:49:26.000 Then they seem happy with what they've got. But they also seem to want to go to higher power and they may need more density, out of it for that and then they'll have to work out a way to address that. 00:49:26.000 --> 00:49:34.000 We have to worry about the wavelength and the conditionality, depending on what kind of, 00:49:34.000 --> 00:49:50.000 drive, drive you want What if you want to try and be getting this double layer type of fact, that's going to be a low density, low thrust sort of plasma, and you'll have to accept that and you're going to have to make sure you've matched the face speed 00:49:50.000 --> 00:49:54.000 correctly to get that. 00:49:54.000 --> 00:50:05.000 And I guess that's kind of what I just said collision listen collision operation that'll drive up what your source is going to be able to do in terms of propulsion. 00:50:05.000 --> 00:50:24.000 I will say, it's not this talk, but I did analyze a generic Helikon source for its performance as a magnetic nozzle but that's a again this is that's a separate case than what I'm talking about here with the electron beams in whether they can actually 00:50:24.000 --> 00:50:30.000 provide some acceleration in themselves. 00:50:30.000 --> 00:50:40.000 And then that leaves be done. 00:50:40.000 --> 00:50:50.000 Thank you very much. 00:50:50.000 --> 00:50:51.000 Explain. 00:50:51.000 --> 00:51:03.000 This is related but the 00:51:03.000 --> 00:51:08.000 scribe Ross production. 00:51:08.000 --> 00:51:16.000 Those were actually, I mean, those have the expanding magnetic fields nozzle sort of thing going on. 00:51:16.000 --> 00:51:21.000 And there's actually. 00:51:21.000 --> 00:51:27.000 It's one of those nomenclature things are semantics things is there's. 00:51:27.000 --> 00:51:32.000 You can get you can get a and b polar. 00:51:32.000 --> 00:51:43.000 You can get a potential drop and an expanding magnetic field in these because the electrons are are frozen to the magnetic field lines, and the ions are not and the electrons expand. 00:51:43.000 --> 00:51:53.000 And then you, and then in in speed up because their temperature gets converted into actual energy, and the ions have to follow for charge neutrality. 00:51:53.000 --> 00:51:58.000 And that looks like a potential drop to. It's not a double layer. 00:51:58.000 --> 00:52:04.000 And depending on who you talk to, whether they'll call it that or not. 00:52:04.000 --> 00:52:23.000 I, this would be a separate one, and then I, I guess I haven't done it where I tried to combine both where it's, it's an expanding magnetic field with this beam, showing up to, to accelerate it, I would say, the little bit critical here but there one 00:52:23.000 --> 00:52:39.000 a little bit critical here but there one paper I saw where there was a double layer and an eye on being being accelerated out of the discharge with right down the center, which is the equivalent to saying that, you know, the earth's magnetic pole is, 00:52:39.000 --> 00:52:46.000 is generating trust with the particles of escape, right down the center. 00:52:46.000 --> 00:53:06.000 The rest of it was just a hemisphere of plasma all at the same energy which was much lower than that game but you know that I think I did the calculation and that is the beam ISP from just how much was it was in the beam, increase the ISP of that thruster 00:53:06.000 --> 00:53:08.000 by five seconds. 00:53:08.000 --> 00:53:21.000 So it was really, physically, you could call it a beam but, I mean, a double layer being but it was very localized I stopped what I usually call a number where. 00:53:21.000 --> 00:53:27.000 So just to follow up on that. Or is it possible to get 00:53:27.000 --> 00:53:32.000 a job. 00:53:32.000 --> 00:53:33.000 Go somewhere without outfit. 00:53:33.000 --> 00:53:54.000 somewhere without some outfit. Yeah, I mean I tried to include in this that once that starts showing up the electrons come backwards. And so it actually reduces, you know, so it was, it was like an added equation that was trying to use to it to. 00:53:54.000 --> 00:54:16.000 So that beam was actually partially retarded, by, by that potential to the degree that it matched what electrons might be drifting backwards. I'm not saying I got it right but I did try and keep it into, into consideration that women. 00:54:16.000 --> 00:54:20.000 Yes. So we've got here. 00:54:20.000 --> 00:54:23.000 As a question I feel like I know you're gonna say to. 00:54:23.000 --> 00:54:32.000 Seems like a pretty solid performance if you were to apply this to a thruster with 00:54:32.000 --> 00:54:40.000 with really high density is what he is in your mind, kind of a winner there like where. 00:54:40.000 --> 00:54:44.000 Why is that not as easy as just sort of knowing it. 00:54:44.000 --> 00:54:56.000 Well, I'm not sure I'd seen an experiment where this, I don't have my lab anymore so I have not seen an experiment where I could check this out at these operating conditions. 00:54:56.000 --> 00:55:09.000 So, I mean there are, there have been conditioned, they sure they've run them at these conditions, but not looked for a beam or potential drop or anything and I'm and again this, the traditional sources, not a thruster. 00:55:09.000 --> 00:55:16.000 Right. And this is just a to going into a larger. 00:55:16.000 --> 00:55:21.000 Conceptually, This would be a to going into a larger vacuum chamber. 00:55:21.000 --> 00:55:38.000 And you would see that you have to check to see if you're seeing that beam at the edge with enough pumping and such. So my other point would be, it's zero D. 00:55:38.000 --> 00:55:59.000 And I don't know that, going back to the double layer question, somebody does zero D on a double layer or even a magnetic field expansion fact I did you know an analysis on a mega, you know, quasi Wendy expansion in a magnetic field without the beam. 00:55:59.000 --> 00:56:10.000 And that's great but it's really just talking about the center line. And 00:56:10.000 --> 00:56:20.000 in the case of the magnetic fields especially poignant that, you know, you don't know where it stops expanding along the magnetic field, so that it. 00:56:20.000 --> 00:56:23.000 It may not be. 00:56:23.000 --> 00:56:27.000 It's probably not going to be as efficient as you'd like it to be. 00:56:27.000 --> 00:56:50.000 And like I said, you do that analysis. 00:56:50.000 --> 00:56:59.000 That's, that's my husband's 00:56:59.000 --> 00:57:04.000 motivation for him. 00:57:04.000 --> 00:57:08.000 Because your comments on your new account, and you know, if you need it. 00:57:08.000 --> 00:57:12.000 Well, the idea is is that's because it's still going to be polar. 00:57:12.000 --> 00:57:31.000 So I, you're in ideally that would be taken care of that instills net zero current going across, it's just because of the, the non Maxwell and electrons you do get some ions coming out as well. 00:57:31.000 --> 00:57:39.000 I'm not proposing doesn't thruster I'm just, but it's i given that people have been trying to do that 00:57:39.000 --> 00:57:41.000 in varying ways. 00:57:41.000 --> 00:57:52.000 It just, I just wanted to test that idea that possibility with because when I realized that my model could try and try and address that. But, um, 00:57:52.000 --> 00:58:00.000 yeah so in that sense it, the ideal deal would be that it's still a and b polar. 00:58:00.000 --> 00:58:17.000 But again, I haven't seen an experiment that would have shown the existence of a beam in an empty polar expansion and acceleration out of the out of the chamber. 00:58:17.000 --> 00:58:25.000 Like, you should see at the bottom so it's like Final. 00:58:25.000 --> 00:58:51.000 Um, yeah yes yes Do I have a basically an estimate of what's the power going into the ionization the ionization costs, and I was using it was like 80 or 180, some somewhere between 80 and 100 ev privatization. 00:58:51.000 --> 00:59:02.000 And, you know, it's interesting is when I was doing the power balance at one point I tried to put in hydrogen instead of argon, it doesn't change much. 00:59:02.000 --> 00:59:20.000 But for different reasons, the ionization cost is lower, but the loss of hydrogen the bone speed of the hydrogen is so much higher that they almost, I would say they cancel each other out, but it wasn't as dramatic change in the power balances I thought 00:59:20.000 --> 00:59:22.000 it might be. 00:59:22.000 --> 00:59:30.000 Not for the, that's not the end pole or anything that was just for the general power balance article 00:59:30.000 --> 00:59:35.000 that was, that was my last thing I threw it at the end of my thesis. 00:59:35.000 --> 00:59:43.000 Change the gas 00:59:43.000 --> 00:59:50.000 depletion Do you have to see your experiments there these relaxation like predator prey. 00:59:50.000 --> 00:59:56.000 I did at the, 00:59:56.000 --> 00:59:58.000 The pressure was high enough. 00:59:58.000 --> 01:00:02.000 Where was I. 01:00:02.000 --> 01:00:06.000 Yeah, 01:00:06.000 --> 01:00:14.000 right there I got to to oscillations there. 01:00:14.000 --> 01:00:25.000 But I had to have enough pressure, I had to have enough neutrals, to be able to backfill in as after a dropped and, and the ionization drops, and then they would flow. 01:00:25.000 --> 01:00:32.000 Basically they were flowing back in and then it could do at once but if it's, you know, these other cases. 01:00:32.000 --> 01:00:38.000 This was a 30 minute tour. 01:00:38.000 --> 01:00:41.000 And again for my model. 01:00:41.000 --> 01:00:57.000 I could get that kind of an oscillation I don't have it here, but I had to raise the background pressure higher than what my experimented had. And then I would see that relaxation oscillation. 01:00:57.000 --> 01:01:04.000 So it wasn't perfect, but 01:01:04.000 --> 01:01:07.000 questions. 01:01:07.000 --> 01:01:20.000 And thank you very much.