Where's the beef?

[choff]

Art, if your calculations prove correct, tell your boss from me that you are being badly underpaid, if fact maybe they should put you in charge of iter and cern. You will have caught an error in a few weeks that some of the top names in the game missed for 2 decades.

[jmc]

In another thread I commented

I haven't even seen a calculation telling me that 2 neutrons per pulse from a polywell is a lot. Maybe we should be expecting thousands, but the experiments are a dismal failure.

Does anyone have an answer to that? If we take everything at face value (a risky proposition, but we have to start somewhere), what do these two neutrons per shot tell us about the confinement time? We have to assume we have a decent potential well and a corresponding ion temperature. (You can explain away any poor result by hypothesizing that the temperature was too low for a decent fusion cross section. Before you are allowed to get excited about fusion neutrons, you have to either measure the temperature or assume it was reasonably high.) The fusion rate then gives us a handle on the density. Is this number consistent with the assumption that beta = 1 was reached? That's a side question (but an important consistency check, where few are available). What we want is a confinement time. For that we either need a decay rate of the density or a feed (ionization) rate. Do we have either of these? Or limits on them? If not, then why are the fusion neutrons seen as so encouraging? They could be the result of simply driving a lousy machine hard enough. (Of course, if we ever get that far, I will want to convert the confinement time to an effective loss area, which I will then compare to various combinations of the system radius and the electron gyroradius. But I know how to do that part myself.)

I believe Bussard injected 1kA of current in at 10kV for WB-6 that and wequivalent heating power input of 10 MW. He got 10^9 neutrons per second out for D-D. Thats an equivalent, roughly of 10^12 for D-T.
10^12*1.6*10^-19*17*10^6=2.72 Watts. If this calculation is correct this represents a q value of 3*10^-7.

[jmc]

Sorry, doubled checked his askmar paper. The emmitter current was 40 amps, not 1 kiloamp this increases the Q-DT by a factor of 25 to 7.5*10^-6

[jmc]

Earlier in this thread Tom Ligon mentioned 14 amps of drive current for WB-6. Considering the crude fueling system and short pulse, this may not be enough to deduce anything much.

I am assuming (one of many big ifs) that convection is the predominant energy loss mechanism. If the 14 amps of drive current is the particle feed rate, then that is (14Cb/s)/(1.6e-19Cb/particle) ~ 1e20 particles/s. The particle inventory is around V*P/kT ~ (5e-4 m^3)*(4e3 Pa)/(1.6e-19 J/eV * 1e4 eV) ~ 1e15 particles, so the confinement time is (could conceivably be) on the order of 10 microseconds. The electron transit time is R/v = R/sqrt(2kT/m) = (5e-2 m)/sqrt(2*(1.6e-19 J/eV)*(1e4 eV)/(9.1e-31 kg)) ~ (5e-2 m)/(60 m/microsecond) ~ 1 ns, so the confinement factor is (1e-5 s)/(1e-9 s) = 1e4. We will have to consider within how many orders of magnitude we trust this result and whether it is a relevant calculation at all. For now I simply note that it is (I believe) on the order of (R/rho)^2, consistent with confinement like point cusps, but not necessarily inconsistent with confinement like line cusps, (R/rho)^1. In both cases without any credit for recirculation.

If the electron particle inventory mainly came from the emitter, and we assume that electrons dominate the ions, by even a factor of two, the 1e15 particles times 1.6*10^-19c= a net charge of 1.6e-4 Coulombs.

V=Q/(4*pi*epsilon_0*r) taking q as 1.6*10-4 Coulombs and r as 0.3 metres yields V=4MV!!! Therefore most of the electrons must have come from the ionized neutrals off the gas feed.

My hunch is the ions kept the electrons in and slowly leaked out through the cusps themselves though I would love to see data.

[D Tibbets]

[quote="jmc
If the electron particle inventory mainly came from the emitter, and we assume that electrons dominate the ions, by even a factor of two, the 1e15 particles times 1.6*10^-19c= a net charge of 1.6e-4 Coulombs.

Um... I'm confused. My understanding is that there are a few million more electrons in the Polywell than ions, so the ratio would be something like ~1.000000001
(1x10e6 excess electrons + ~1x10e15 electrons produced with the ions)/ ~1x10e15 ions

[Art Carlson]

Art, if your calculations prove correct, tell your boss from me that you are being badly underpaid, if fact maybe they should put you in charge of iter and cern. You will have caught an error in a few weeks that some of the top names in the game missed for 2 decades.

I hate to tell you this, but the top names in fusion research have never even heard of the polywell.

[jmc]

D Tibbets, my point was that all the electrons aren't provided by the emmitters, many come from the newly ionized gas.

[TallDave]

I hate to tell you this, but the top names in fusion research have never even heard of the polywell.

Seems likely far more people know Bussard's name than the names of any of the top tokamak researchers.

[D Tibbets]

D Tibbets, my point was that all the electrons aren't provided by the emmitters, many come from the newly ionized gas.

Yes, but at least with deuterium you can only have one free electron produced for each duterium ion formed.

[rnebel]

jmc:

For Polywell reactors, none of the electrons will come from ionized gas.

[MSimon]

jmc:

For Polywell reactors, none of the electrons will come from ionized gas.

Wouldn't there be electrons left behind from fusion alphas?

[blaisepascal]

jmc:

For Polywell reactors, none of the electrons will come from ionized gas.

Wouldn't there be electrons left behind from fusion alphas?

The claim I've been hearing is that there are up to two populations of electrons in the reactor: The electrons intentionally injected into the well and confined magnetically to create the virtual cathode, and the electrons separated from the ions. The electrons in the well are trapped by the magnetic fields and can't get out of the well, and the electrons from the ions don't have enough energy to climb into the well in the first place. So the populations are kept separate.

[rnebel]

M Simon:

The alphas leave the nucleous positively charged. When they exit the device, it will become more negatively charged. However, those electrons don't necessarily come from ionization. They can come from anywhere.

Blaispascal:

A lot of people think that, but that's wrong. If you do that you end up with Art Carlson's ambipolar losses. If you want, I'll give you about a 4 line proof as to how that works. Fill pressures on all virtual cathode devices (like Polywells) are always tiny (typically 3-4 orders of magnitude less than Tokamaks).