Ok, I've got to find a research topic for my Honors project, so I was wondering what kind of things related to BFR I might be able to investigate on a small scale/budget? I know drmike has been talking about building a vacuum system, so maybe we could discuss that sort of project. My school definitely can't afford an entire WB-7 copy, plus
I haven't really done any work with vacuum, plasma diagnostics, etc so I'm thinking this might be too ambitious. Alternatively, I've thought about doing a modeling project, since I know a bit of C++. That may be more practical.
Anyway, I was just wondering whether there might be any little bite-sized peices of work that I could take on that might be of some value but at the same time not too much for a noob. (And especially Dr. Nebel, if you've got any suggestions I'd love to hear them!)
Undergrad polywell research?
I think I have a way to build a polywel on a budget. Get one of those 6 port uhv crosses. And wrap each arm with magnet wire to the desired size. On the inside you fashion an electrode around the centre where the 6 pipes come in, making sure it has a low profile to allow electron flow through the centre of the pipes, and have it attach through a feed through on one of the fittings which goes to a +HV supply. On another fitting you put your electron source, ion source, and instrumentations. You may not be able to do fusion but I think it should do some electron confinement and test well depth and beta scaling.
It can't recirculate along line cusps of course but will on the point cusps.
It can't recirculate along line cusps of course but will on the point cusps.
Carter
Time is the critical thing. If you have a year, you can think about an experiment. If you only have 3 to 6 months, stick with software. Experiments require parts, and sometimes you have to wait for things to show up, or wait to get into the shop so you can build things. Software you can pound on 24 hours straight, get 2 hours of sleep and do it again.
Experiments also take up space. You need a place to set things up that can sit for a long time (like a year!) So ask your advisor if you have enough time and space for an experiment, and if not, do a software study. You will learn a lot either way, but the constraints you are under now dictate which way makes the most sense.
Experiments also take up space. You need a place to set things up that can sit for a long time (like a year!) So ask your advisor if you have enough time and space for an experiment, and if not, do a software study. You will learn a lot either way, but the constraints you are under now dictate which way makes the most sense.
drmike: Thanks, that sounds like good advice. I think I've got more like 1.5 yrs to work on it, depending on certain deadlines. I'm going to be a junior, and I think you only have to wrap the whole project up by the end of senior year, but I imagine they might want some kind of proof of progress before then. I also think I could come up with some space for it, the physics shop is pretty much unused AFAIK.
kcdodd: hmm, I'll have to think about that. It might work, but the main problem I see is that I'd expect most of the cusp losses to be from the corner cusps rather than point cusps, and I think some of the closed box machines had problems with neutral ionization when the electron beams from the cusps hit the walls.
I was wondering, would a smaller machine (10 cm? 15?) be worthwhile? It would technically test scaling, but not really since you'd have to extrapolate more than interpolate to get to useful machine size. The advantages would be ease of fabrication and also lower B-field required, so more friendly power supply size. Of course, it might be more difficult to get instrumentation on a smaller version.
kcdodd: hmm, I'll have to think about that. It might work, but the main problem I see is that I'd expect most of the cusp losses to be from the corner cusps rather than point cusps, and I think some of the closed box machines had problems with neutral ionization when the electron beams from the cusps hit the walls.
I was wondering, would a smaller machine (10 cm? 15?) be worthwhile? It would technically test scaling, but not really since you'd have to extrapolate more than interpolate to get to useful machine size. The advantages would be ease of fabrication and also lower B-field required, so more friendly power supply size. Of course, it might be more difficult to get instrumentation on a smaller version.
Actually, at low beta I think its just the opposite. The face point cusps are at low field values, so most of the loss would be there. The line and corner cusps have high field strength because they are very close together. I am not saying you will be able to beat the open core design but for an undergraduate research project I think it would be a good setup and would try it myself if I had the equipment. If you are able to get to the point where line cusps are the major loss then you are probably at least some-what high density. A good place to run tests. And it being such a small chamber and the coils being on the outside it would be much easier to construct and power and cool etc.
The cross itself would be the most expensive part depending on if your department has one already or not. And a feedthrough for HV and magnet DC. Of course, the biggest would be if your dept has vacuum equipement. If not that would be a killer. Most have power supplies etc though. But I was once able to get the end of a giant spool of magnet wire for free from a motor repair shop just by saying it was for a school project and I bet you could build it in a couple days of winding, tedious work.
Be ambitious, you learn the most that way.
edit:
Although I just happened to think if the cross is steel the magnetic field might not actually penetrate. Not sure how the polarization would react. Do they make aluminium ones? Although then you have temperature issues.
The cross itself would be the most expensive part depending on if your department has one already or not. And a feedthrough for HV and magnet DC. Of course, the biggest would be if your dept has vacuum equipement. If not that would be a killer. Most have power supplies etc though. But I was once able to get the end of a giant spool of magnet wire for free from a motor repair shop just by saying it was for a school project and I bet you could build it in a couple days of winding, tedious work.
Be ambitious, you learn the most that way.
edit:
Although I just happened to think if the cross is steel the magnetic field might not actually penetrate. Not sure how the polarization would react. Do they make aluminium ones? Although then you have temperature issues.
Carter
If you can find a 6 way cross you can do quite a few experiments fairly cheaply. The nice thing about having the coils external is that you can fix them when things go wrong without taking your vacuum system apart. It also gives you ports to put in diagnostics so you can measure currents and densities. You'd still need an internal grid or 2, but with multiple ports they would be easy to feed. It might be closer to a "magnetic fusor" rather than the full MaGrid form, but so what - you'll learn a lot of physics!
Hmm, I think the magnet placing is the best thing going for that idea. Well, and the fact that magnet power supply doesn't have to float at umpteen kV. Maybe you are right about the recirc, I don't know. One other thing to consider is that some of the B-field lines will go straight thru the grid.
I think we have a nice high vacuum pump setup (rough pump, mercury diffusion and cold trap), probably some kind of HV, but I doubt they have a cross. You can buy aluminum ones, but I bet they'd be even pricier. Feedthrus would be another problem.
I was thinking, with lower B-fields and electron energies, whiffleball condition should still be achievable, althought at lower electron/plasma densities. MAybe with the right coils, the whiffleball can be established gradually by the slower process Dr. B mentions (ramp the grid voltage and B-field, instead of starting high and requiring instant ionization of puffed gas supply). The limiting factor here would be the magnet heating; I don't think cooled magnets are an option. (Of course, if the magnets were external to the chamber, aircooling would occur.) But it should be possible to measure densities and potentials and trapping even at low well depth/Bfield/density, right?
Edit: drmike: yet another good reason to have the coils external! One more thing I thought of: it'll put the electrostatic saddle point inside the cusp throat, so electrons will be decellerated by the e-field and that ought to increase the mirror confinement, so densities may be higher than otherwise. That's certainly worth looking at.
I think we have a nice high vacuum pump setup (rough pump, mercury diffusion and cold trap), probably some kind of HV, but I doubt they have a cross. You can buy aluminum ones, but I bet they'd be even pricier. Feedthrus would be another problem.
I was thinking, with lower B-fields and electron energies, whiffleball condition should still be achievable, althought at lower electron/plasma densities. MAybe with the right coils, the whiffleball can be established gradually by the slower process Dr. B mentions (ramp the grid voltage and B-field, instead of starting high and requiring instant ionization of puffed gas supply). The limiting factor here would be the magnet heating; I don't think cooled magnets are an option. (Of course, if the magnets were external to the chamber, aircooling would occur.) But it should be possible to measure densities and potentials and trapping even at low well depth/Bfield/density, right?
Edit: drmike: yet another good reason to have the coils external! One more thing I thought of: it'll put the electrostatic saddle point inside the cusp throat, so electrons will be decellerated by the e-field and that ought to increase the mirror confinement, so densities may be higher than otherwise. That's certainly worth looking at.