Not sure if this should be design or theory, but here goes.
I'm an undergrad student, I'd like to do some research, but I don't know much about fusion. So I've been looking at trying to do research on the wiffleball effect.
My school doesn't seem to have an UHV chamber for undergrad use (wonder why?) so I'm wondering how hard the vacuum has to be for wiffleball conditions. I know that it has to be on the order of 1E-8 torr for fusion, but that mostly seems to be about arcing and fuel poisoning. Could I form a wiffleball with cheaper equipment?
Low Pressure Wiffleball
Low Pressure Wiffleball
Last edited by JohnSmith on Sun Aug 10, 2008 9:30 pm, edited 1 time in total.
I'm looking into the same kind of thing myself (undergrad research.) hmm. From Dr. B's papers, looks like they expected arcing to start ~ 3E-6 Torr. Of course, it depends on the applied voltage, spacing, and construction (presence of sharp points, quality of insulating standoff/feedthru). It's not imperative to have fusion-relevant ion temperatures for what we're looking at, so perhaps a lower drive voltage could allow a higher initial neutral pressure, in terms of arcing.
As far as the effect of pressure on the whiffleball, I'm not sure how much it can stand. The machine will ionize the neutrals and draw them in, so the background pressure will drop when the machine runs. (Fusors do this too). But I guess the bottom line is that you probably need a pretty decent vacuum system, unfortunately. I'm going to guess you'll need at least 1e-4Torr, maybe more like 1e-6.
drmike, Tom, care to chime in?
As far as the effect of pressure on the whiffleball, I'm not sure how much it can stand. The machine will ionize the neutrals and draw them in, so the background pressure will drop when the machine runs. (Fusors do this too). But I guess the bottom line is that you probably need a pretty decent vacuum system, unfortunately. I'm going to guess you'll need at least 1e-4Torr, maybe more like 1e-6.
drmike, Tom, care to chime in?
How do you expect to create the wiffle ball at low cost?
1. Magnetic field
2. Electron gun
3. Ion/electron separation
4. Open box machine
To get results other than suggestive you would need runs in the 100 ms range absolute minimum.
I would think POPS in a Farnswortrh type machine would be far easier and quite useful.
1. Magnetic field
2. Electron gun
3. Ion/electron separation
4. Open box machine
To get results other than suggestive you would need runs in the 100 ms range absolute minimum.
I would think POPS in a Farnswortrh type machine would be far easier and quite useful.
Engineering is the art of making what you want from what you can get at a profit.
I'm not sure I understand you. Are those four things problems?
1) Coils are cheap(ish) and easy
2) Electron guns are common, though I'm not sure if ripping apart an old tv is a good idea. I'll probably die of heavy metal poisoning instead of radiation poisoning.
3) Might be a problem. I understand that in the WB machines, it ionizes automatically. Needs looking into.
4) Not sure what you mean.
And yes, I'd be hoping to get steady state.
For my current idea, I'm actively trying to avoid fusion. I don't understand it near well enough, and my landlady would almost certainly object to me irradiating her cats.
I've been watching the attempts at field solvers, and they keep coming back to, "not sure if I modeled it quite right." I'd like to fiddle with the wiffleball, and try and verify some of the results that are floating around.
On the other hand, Exams are done! Now I actually have time to study the wiki article, and maybe find a textbook on fusion.
1) Coils are cheap(ish) and easy
2) Electron guns are common, though I'm not sure if ripping apart an old tv is a good idea. I'll probably die of heavy metal poisoning instead of radiation poisoning.
3) Might be a problem. I understand that in the WB machines, it ionizes automatically. Needs looking into.
4) Not sure what you mean.
And yes, I'd be hoping to get steady state.
For my current idea, I'm actively trying to avoid fusion. I don't understand it near well enough, and my landlady would almost certainly object to me irradiating her cats.
I've been watching the attempts at field solvers, and they keep coming back to, "not sure if I modeled it quite right." I'd like to fiddle with the wiffleball, and try and verify some of the results that are floating around.
On the other hand, Exams are done! Now I actually have time to study the wiki article, and maybe find a textbook on fusion.
If you look in the Design forum, I talked with kcdodd and drmike a bit about experimental setup. We didn't get too far, but one thing that came out was the idea of using external magnets, which is what I think MSimon was saying. It won't properly test some aspects of the Polywell, but you should still be able to create a whiffleball. One potential problem is that a steel chamber might sheild out the B-field if the coils are outside. I don't know how bad it would be though.
Let me start off with this thought. If it is so cheap and easy why did Dr. B go to a pulsed machine, which would give more room for doubts?JohnSmith wrote:I'm not sure I understand you. Are those four things problems?
1) Coils are cheap(ish) and easy
2) Electron guns are common, though I'm not sure if ripping apart an old tv is a good idea. I'll probably die of heavy metal poisoning instead of radiation poisoning.
3) Might be a problem. I understand that in the WB machines, it ionizes automatically. Needs looking into.
4) Not sure what you mean.
And yes, I'd be hoping to get steady state.
For my current idea, I'm actively trying to avoid fusion. I don't understand it near well enough, and my landlady would almost certainly object to me irradiating her cats.
I've been watching the attempts at field solvers, and they keep coming back to, "not sure if I modeled it quite right." I'd like to fiddle with the wiffleball, and try and verify some of the results that are floating around.
1. What kind of field do you expect?
2. What about high voltage?
3. Coil cooling?
4. Small machines need more electron injection (according to some theories)
5. Closed box machines (external coils) require more electron injection to make up for losses
6. The wiffle ball effect depends on electrons circulation near coils. Will the electron circulation be close enough if the coils are on the outside of the machine?
Doing POPS on a fusor or pB on a fusor would be just as important experimentally and could be done with a lot lower budget and a greater chance that the experimental set up would work.
Engineering is the art of making what you want from what you can get at a profit.
Well, a fair bit of this requires number crunching. More stuff for my free time.
But if I recall correctly, Dr. B did go steady state for a while, before going up to pulsed machines. I'm hoping to dodge the high voltages and cooling problems by going small.
And I've really got no idea why he wouldn't have built a pure wiffleball test system. It would have saved a lot of arguing on our part if we had that data... On the other hand, we don't have much data on what he did build!
I don't want external coils, I'd like internal ones. Recirculation and all that. Yes, cooling is a problem. More numbers.
And since internal coils means a bigger vacuum chamber, I want to get away with the worst vacuum possible.
Maybe the POPS fusor or pBj fusor are better experiments, I don't know. But I think this idea is worth fleshing out. Unless we get the data at the end of the month.
But if I recall correctly, Dr. B did go steady state for a while, before going up to pulsed machines. I'm hoping to dodge the high voltages and cooling problems by going small.
And I've really got no idea why he wouldn't have built a pure wiffleball test system. It would have saved a lot of arguing on our part if we had that data... On the other hand, we don't have much data on what he did build!
I don't want external coils, I'd like internal ones. Recirculation and all that. Yes, cooling is a problem. More numbers.
And since internal coils means a bigger vacuum chamber, I want to get away with the worst vacuum possible.
Maybe the POPS fusor or pBj fusor are better experiments, I don't know. But I think this idea is worth fleshing out. Unless we get the data at the end of the month.
The nice thing about POPS or pB in a fusor is that the data will be useful no matter what the results are at the end of the month.JohnSmith wrote:Well, a fair bit of this requires number crunching. More stuff for my free time.
But if I recall correctly, Dr. B did go steady state for a while, before going up to pulsed machines. I'm hoping to dodge the high voltages and cooling problems by going small.
And I've really got no idea why he wouldn't have built a pure wiffleball test system. It would have saved a lot of arguing on our part if we had that data... On the other hand, we don't have much data on what he did build!
I don't want external coils, I'd like internal ones. Recirculation and all that. Yes, cooling is a problem. More numbers.
And since internal coils means a bigger vacuum chamber, I want to get away with the worst vacuum possible.
Maybe the POPS fusor or pBj fusor are better experiments, I don't know. But I think this idea is worth fleshing out. Unless we get the data at the end of the month.
Engineering is the art of making what you want from what you can get at a profit.
Well, recirculation is not the same as the whiffleball effect. You can get a whiffleball without it, althought it's probably true that the electron injection current will need to be higher to make up for losses. There might be some issues with neutral outgassing from the walls where the electron beams out the cusps hit the walls, though.
The reason I was arguing for external coils was based on several factors: 1) the coils would be aircooled, and so steady state (or at least long pulsed) operation would be possible. I'd need this if I wanted to try the slower transition of gradually building up the B-field to create the whiffleball. Plus it would make data acquisition better, and give info about steady state operation. 2) Easier to construct external coils: no conformal cans that have to be smooth, HV feedthru wouldn't have to support such a large object. 3) easy access in case something goes south or I want to tinker with options like adding more turns, wouldn't have to break vacuum.
If I plan on running the thing at low voltages, say in the range 5-10kV, then it shouldn't be too hard to come up with a feedthru that can handle this, and also a PS that could put out some higher current (would 50-100 mA be enough? More?)
MSimon: yeah, you've got a point about Dr. Nebel's work kind of making some of the info I'd gather redundant, but maybe that's not such a bad thing. Of course, I'm going to wait to see, if nothing else, what timeframe we can expect to find out more details, before I decide on a course of action.
The reason I was arguing for external coils was based on several factors: 1) the coils would be aircooled, and so steady state (or at least long pulsed) operation would be possible. I'd need this if I wanted to try the slower transition of gradually building up the B-field to create the whiffleball. Plus it would make data acquisition better, and give info about steady state operation. 2) Easier to construct external coils: no conformal cans that have to be smooth, HV feedthru wouldn't have to support such a large object. 3) easy access in case something goes south or I want to tinker with options like adding more turns, wouldn't have to break vacuum.
If I plan on running the thing at low voltages, say in the range 5-10kV, then it shouldn't be too hard to come up with a feedthru that can handle this, and also a PS that could put out some higher current (would 50-100 mA be enough? More?)
MSimon: yeah, you've got a point about Dr. Nebel's work kind of making some of the info I'd gather redundant, but maybe that's not such a bad thing. Of course, I'm going to wait to see, if nothing else, what timeframe we can expect to find out more details, before I decide on a course of action.
Don't forget, the promised time frame for results was the end of this month. If we get the data, we probably won't have gotten anything more than design work done, so nothing really lost. If we don't get any data, that means that the DoD is trying to keep the work under wraps, which makes me want to work on it even more.
Simon, following the links on your power and control blog brought me to a paper by Nebel on building a POPS fusor. Are the results not public?
Solo, we've got different ideas on what 'low voltage' means! I was thinking of the 500V - 1kV range. I've still got to do the math to see if it's even possible... Though I'm not sure why it wouldn't be. I'd just have a really shallow potential well.
Simon, following the links on your power and control blog brought me to a paper by Nebel on building a POPS fusor. Are the results not public?
Solo, we've got different ideas on what 'low voltage' means! I was thinking of the 500V - 1kV range. I've still got to do the math to see if it's even possible... Though I'm not sure why it wouldn't be. I'd just have a really shallow potential well.
Yeah, I think Simon's right: if you want to do something useful, POPS is probably more helpful. I get the impression evaluating the WB claims was a major focus for Nebel's team, and it sounds like they have a ton of data that will be reviewed and analyzed by expert peers.
Worst-case, if the project is dropped, you would then probably have access to that data, or be able to buy a WB-7 from EMC2 to do your own study (if you have backing/funding).
Here's some POPS citations from Barnes and Nebel (hehe):
http://icc2006.ph.utexas.edu/abstract.php?view=87
Worst-case, if the project is dropped, you would then probably have access to that data, or be able to buy a WB-7 from EMC2 to do your own study (if you have backing/funding).
Here's some POPS citations from Barnes and Nebel (hehe):
http://icc2006.ph.utexas.edu/abstract.php?view=87
There are things that haven't been tried re: POPS. Multi-gridded designs for instance.
Also POPS has not been done in a machine that produces actual fusion. D-D would be the gold standard there.
As to insulators. It is hard to get ones rated under 20 KV for any kind of HV work and 50 KV is common. So exploring the pB11 50 - 65 KV resonance peak of pB in a fusor is not unreasonable. Ordinary Boron could be used to keep the costs down with a slight loss of efficiency (20%).
An ordinary spark plug can be pushed to 30 to 35 KV for DC supplies.
Also POPS has not been done in a machine that produces actual fusion. D-D would be the gold standard there.
As to insulators. It is hard to get ones rated under 20 KV for any kind of HV work and 50 KV is common. So exploring the pB11 50 - 65 KV resonance peak of pB in a fusor is not unreasonable. Ordinary Boron could be used to keep the costs down with a slight loss of efficiency (20%).
An ordinary spark plug can be pushed to 30 to 35 KV for DC supplies.
Engineering is the art of making what you want from what you can get at a profit.
Hmm. Ok, <1kV it is then! And you could definitely use spark plug feed-thrus with that. I guess the low drive energy will limit the plasma pressure developed, but that's ok because you aren't going to get huge B-fields anyway. A number of mirror plugging experiments run with that kind of well potential. I suppose the density could still be high, though, due to the low particle energy.
Unfortunately, I just got an email back from my advisor who doesn't think I can do any plasma work with the equipment and funds at my school. So much for my polywell experiments. But I'd still like to hack out a design.
Unfortunately, I just got an email back from my advisor who doesn't think I can do any plasma work with the equipment and funds at my school. So much for my polywell experiments. But I'd still like to hack out a design.
Am I missing something? The paper I referred to earlier, it was talking about a fusor using POPS as if it was under construction. Was that machine a failure? If so, I'm not too confident of my chances to build it cheap.MSimon wrote: Also POPS has not been done in a machine that produces actual fusion. D-D would be the gold standard there.
It's not that I'm against building a fusor; I'd love to. But I can't see it being less expensive than a simple, small WB. And I've got to convince a professor at a school that's known for it's computer work to help me.
Anyway, value of the experiment aside, does anyone have any idea on how to calculate the maximum pressure to form a wiffleball?