All that can go wrong with recirculation
I assume that is for the electron beam since it's outside. And I am assuming you are counting the length along parallel to the electron beam. If so doesn't that seem to say that all the reflection has to occur within 7cm of the magrid?
On your earlier comment, its easy to make the confinement time smaller to prevent thermalization but I doubt you would want to do that on purpose since that defeats the purpose.
On your earlier comment, its easy to make the confinement time smaller to prevent thermalization but I doubt you would want to do that on purpose since that defeats the purpose.
Carter
Taking Beta=1, a field of 1 Tesla and a temperature of 100KV the density you get is 2.4e19 particles per m^3, using S.I. units this gives a debye length of 481 microns and a larmor radius of 1066 microns.
Interestingly enough this does not change with increasing magnetic field as the debye length goes down with the inverse of the square root of the density increase, taking beta=1 the density is propotional to the square of the magnetic field this makes the debye length inversely proportional to the first power of the magnetic field just like the larmor radius.
Having said that even if the debye length is similar to the cusp width it doesn't change the fact that
a) there will be an untenably dense electron cloud beyond the cusp
and:
b) the electrons cannot be electrostatically confined by the ions or else they would not be electrostatically confining the ions.
I still stich to my few of ions flowing through loss areas whose dimensions are of order an electron larmor orbit.
Interestingly enough this does not change with increasing magnetic field as the debye length goes down with the inverse of the square root of the density increase, taking beta=1 the density is propotional to the square of the magnetic field this makes the debye length inversely proportional to the first power of the magnetic field just like the larmor radius.
Having said that even if the debye length is similar to the cusp width it doesn't change the fact that
a) there will be an untenably dense electron cloud beyond the cusp
and:
b) the electrons cannot be electrostatically confined by the ions or else they would not be electrostatically confining the ions.
I still stich to my few of ions flowing through loss areas whose dimensions are of order an electron larmor orbit.
kcdodd:
It's actually an interesting question. All of these systems assume particle flowthrough. Generally, Polywells try to operate at higher densities (than other magnetic confinement machines) so the confinement time constraints aren't as stringent as they are in most magnetic confinement devices. Ion focussing will also help the power balance by raising the reactivity. There are several components that come into the power balance. The strategy is that if one gives you a problem, you compensate for it elsewhere. Its also worth noting that energy confinement times and particle confinement times are not the same thing. Many electrostatic devices cycle a lot of electrons through them but not much energy. The Penning trap worked this way. When you remove a prticle from the top of the potential well, you don't lose a lot of energy.
The point of the statement at the end of my last post is that with the present generation machine the electrons aren't in the machine long enough to test thermalization.
It's actually an interesting question. All of these systems assume particle flowthrough. Generally, Polywells try to operate at higher densities (than other magnetic confinement machines) so the confinement time constraints aren't as stringent as they are in most magnetic confinement devices. Ion focussing will also help the power balance by raising the reactivity. There are several components that come into the power balance. The strategy is that if one gives you a problem, you compensate for it elsewhere. Its also worth noting that energy confinement times and particle confinement times are not the same thing. Many electrostatic devices cycle a lot of electrons through them but not much energy. The Penning trap worked this way. When you remove a prticle from the top of the potential well, you don't lose a lot of energy.
The point of the statement at the end of my last post is that with the present generation machine the electrons aren't in the machine long enough to test thermalization.
jmc:
If we have a problem with low energy electrons choking the cusp, then we'll get rid of them. If they are sitting in the cusp throat then they are at low energy so they aren't doing you any good anyway. You guys are making a bunch of "straw man" arguments where you set up a straw man and then knock him down. You need to start thinking about how to solve problems rather than throwing up your hands and saying it can't be done.
If we have a problem with low energy electrons choking the cusp, then we'll get rid of them. If they are sitting in the cusp throat then they are at low energy so they aren't doing you any good anyway. You guys are making a bunch of "straw man" arguments where you set up a straw man and then knock him down. You need to start thinking about how to solve problems rather than throwing up your hands and saying it can't be done.
I'm sorry if I confused the issue with the cold-elecrons-in-cusp idea. Dr. Bussard thought it was wrong in any case.
That conjecture was not meant to be some complaint that the machine would not work, it was my best guess as to why PXL-1, which should have leaked badly on the corners, would suddenly get very good. Since PXL-1 had no chance of recirculation if anything leaked out the corners, I wondered if cold electrons coming from gas ionization (which my instincts told me should hang as close to the walls as the fields would allow) would slide into the cusps, acting as a repeller plate to the hot population and thus improving confinement.
The thought was the cold electrons might mag-mirror where the hot electrons would be able to leak, but I'm not so sure that's right ... a slow electron also does not interact as strongly with the B field. More likely, the improvement was simply wiffle-ball formation.
I would suggest, if I were a low-energy electron formed in the region close to the magrid where you want to make ions, I'd never be able to go into the potential well. I'd simply hang out at about the potential at which I was born, sliding along the magnetic field "lines" until I found the closest point, in terms of energy, I could reach in the proximity of the magrid. I suspect that is in the magrid openings, although probably not centered. If this is the case, I'd be out of the way, but possibly putting a bit of a negative space charge in the opening, which might have some small beneficial effect by helping steer the leakers into a smaller area. I would not stay between the inner magrid faces and the potential well, since the potential well would repel me, nor would I want to be outside the magrid, and so I would not be in any way blocking the electrostatic "line of sight" driving the hot electrons. Above all, I would not want to cause any trouble, nor would I have the energy to do so.
Since I would stay closer to the magrid than the hot population, I'd be in an excellent spot to ionize fuel. Feed me some microwaves at the ECR frequency for the field strength I reside in, and I'm your ion source.
That conjecture was not meant to be some complaint that the machine would not work, it was my best guess as to why PXL-1, which should have leaked badly on the corners, would suddenly get very good. Since PXL-1 had no chance of recirculation if anything leaked out the corners, I wondered if cold electrons coming from gas ionization (which my instincts told me should hang as close to the walls as the fields would allow) would slide into the cusps, acting as a repeller plate to the hot population and thus improving confinement.
The thought was the cold electrons might mag-mirror where the hot electrons would be able to leak, but I'm not so sure that's right ... a slow electron also does not interact as strongly with the B field. More likely, the improvement was simply wiffle-ball formation.
I would suggest, if I were a low-energy electron formed in the region close to the magrid where you want to make ions, I'd never be able to go into the potential well. I'd simply hang out at about the potential at which I was born, sliding along the magnetic field "lines" until I found the closest point, in terms of energy, I could reach in the proximity of the magrid. I suspect that is in the magrid openings, although probably not centered. If this is the case, I'd be out of the way, but possibly putting a bit of a negative space charge in the opening, which might have some small beneficial effect by helping steer the leakers into a smaller area. I would not stay between the inner magrid faces and the potential well, since the potential well would repel me, nor would I want to be outside the magrid, and so I would not be in any way blocking the electrostatic "line of sight" driving the hot electrons. Above all, I would not want to cause any trouble, nor would I have the energy to do so.
Since I would stay closer to the magrid than the hot population, I'd be in an excellent spot to ionize fuel. Feed me some microwaves at the ECR frequency for the field strength I reside in, and I'm your ion source.
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Art Carlson
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I see that differently. I'd say we're doing your work for you. The available descriptions of polywell operation are neither complete nor consistent. Some explanations contradict other explanations or the laws of physics. We're just trying to find a description that could describe a working machine. Part of that job is coming up with pictures and then kicking the tires. I don't see how we're supposed to solve problems if we don't identify them first.rnebel wrote:You guys are making a bunch of "straw man" arguments where you set up a straw man and then knock him down. You need to start thinking about how to solve problems rather than throwing up your hands and saying it can't be done.
I hadn't thought about that.Inertia is continually injected into the electrons through the electric field and the electrons aren’t confined long enough to thermalize.
Heh, a dynamic system sure looks a lot different than a static one.
That flexibility's one of the things that's always made Polywell especially promising in my eyes. Going to be a lot of fun adjusting the various factors to find optimal settings if this goes forward to a net power attempt.There are several components that come into the power balance. The strategy is that if one gives you a problem, you compensate for it elsewhere.
Seems to me a good way to 'get rid' of low energy electrons would be to hit them with microwaves, turning them into high energy electrons. Something you might want to do anyway if electron injectors aren't needed to maintain balance after the reactor is running.rnebel wrote:If we have a problem with low energy electrons choking the cusp, then we'll get rid of them.
It is an oscillating beam machine. I do not believe electrons will get stuck in the cusps.hanelyp wrote:Seems to me a good way to 'get rid' of low energy electrons would be to hit them with microwaves, turning them into high energy electrons. Something you might want to do anyway if electron injectors aren't needed to maintain balance after the reactor is running.rnebel wrote:If we have a problem with low energy electrons choking the cusp, then we'll get rid of them.
There are two (or three) dominant oscillations. Electrons from outside the reaction space to the reaction space and outside again. Deuterons (or p and B11) from the MaGrid to the center and then to the MaGrid. Each of these is going to have its own frequency. It will be interesting to see if the oscillators become harmonically coupled. I would tend to think so. It may give us another knob to twist by adjusting the POPS waveform. The frequency relationship should be something like sqrt(pm/em) where em is electron mass and pm is proton mass and sqrt(B11m/em) or sqrt(dm/em) where dm is the deuteron mass.
Actual conditions may cause some deviation from those numbers allowing the oscillators to lock.
It is helpful that the electron oscillation is around 60X the frequency of Deuterons. That means that lock at 59X, 60X, or 61X should be possible without a great deal of "pulling".
Protons at 42.5X and B11 at 140.7X may be a little tougher. Not to mention p and B11 frequency at a ratio of 3.3X.
What we need is operation of the machine in a .1 to 1 second range so we can look at the frequencies with fairly good resolution. i.e Experiments.
Engineering is the art of making what you want from what you can get at a profit.
This has also been a source of frustration to me. See viewtopic.php?t=27 for a long discussion of the basic parameters. Most of the papers cited in that thread are over 10 years old. I haven't seen a distribution of measured plasma density or how it is distributed. Has anyone calculated a power density for a realistic machine? I suspect the it would be too low to make it practical, even if it broke even.Art Carlson wrote:The available descriptions of polywell operation are neither complete nor consistent. Some explanations contradict other explanations or the laws of physics. We're just trying to find a description that could describe a working machine.
Fusion is easy, but break even is horrendous.