Focus Fusion On Slashdot

[D Tibbets]

Which causes more bremsstrulung, a near encounter between a fast ion and a slow electron or a fast electron and a slow ion.

http://en.wikipedia.org/wiki/Nuclear_fu ... ic_plasmas

You've got high voltages in there, so you'll be making fast neutrals of a sufficient rate to account for neutrons by irradiation of the interstitial deuterium in the walls of the chamber.

At a rate far higher than anything Farnsworth got at those drive levels, just as the device sweeps through beta=1? Very, very unlikely.

But WB-8 neutron counts should absolutely confirm or disprove fast-fast fusions, since the scaling is so different.

Thanks for the link. I believe the additional penalties for bremsstrahlung mentioned below the table would not apply to Polywells, based on Nebels statment that alphas (and presumably other fusion product ions) bounce around some and them exit a cusp without giving up much of their energy to the plasma, like needs to occur in Tokamacs' or other ignition dependant systems. I'm guessing this and the drive voltages obtainable are what limit these type of systems to only D-T efforts.

Concerning Rider's conclusions. In his 1995 paper abstract he states:
http://adsabs.harvard.edu/cgi-bin/nph-b ... ML&format=

Analytical Fokker-Planck calculations are used to determine accurately the minimum recirculating power that must be extracted from undesirable regions of the plasma's phase space and re injected into the proper regions of the phase space in order to counteract the effects of collisional scattering events and keep the plasma out of equilibrium. In virtually all cases, this minimum recirculating power is substantially larger than the fusion power, so barring the discovery of methods for recirculating the power at exceedingly high efficiencies, reactors employing plasmas not in thermodynamic equilibrium will not be able to produce net power.

.

He hedged a tiny amount by using the word 'virtually' instead of 'absolutely' or other stronger adjective (I know this is grasping at straws).

Two methods advertised for the Polywell that might contribute to "methods for recirculating the power at exceeding high efficiencies" would be ion annealing and especially electron recirculation (claimed 10 X or more increase in energy efficiency). I suppose it boils down to what scale Rider means by "exceedingly high efficiencies" and the validity of the advertised methods ( accepting Riders assumptions and analysis).

Dan Tibbets

[Art Carlson]

People really need to read the available literature before shouting "only three neutrons!" I'm seeing this claim all over and it just isn't true.

You caught me. That's a maximum of 3 neutrons in any one experiment. Since there were four shots that produced neutrons, we are actually talking about a whopping 8 neutrons. Now that's a horse of a different color.

[Art Carlson]

I'm still curious what skeptics think we will see in WB-8/8.1. Beam-background scaling? Ions fleeing through the cusps?

I discussed this here with Rick in detail a while back. I expect particle losses on the order of n*c_s*rho*R, where rho is probably sqrt(rho_e*rho_i), but might be anywhere between rho_e and rho_i. Energy losses should be at least this value multiplied with the drive voltage. Rick has hinted that he has data that show confinement is better than this, but it's still where I place my bet.

[TallDave]

People really need to read the available literature before shouting "only three neutrons!" I'm seeing this claim all over and it just isn't true.

You caught me. That's a maximum of 3 neutrons in any one experiment. Since there were four shots that produced neutrons, we are actually talking about a whopping 8 neutrons. Now that's a horse of a different color.

Again, WB-6 was not the only machine that produced neutrons. We know for a fact earlier machines did, and it's extremely likely WB-7 did as well. It's easier to argue against Polywell while ignoring that, but not as interesting.

Even for WB-6, a larger sample size is obviously significant. If lightning strikes somewhere once precisely at midnight, coincidence. Twice in the same place at exactly midnight, you start to wonder. Three times, you probably avoid standing there at 11:59.

Rick has hinted that he has data that show confinement is better than this, but it's still where I place my bet.

Heh. Well, I thank you for your prediction and salute your intransigence. I'll try to work through the math on that and get some numbers for WB-8 this week.

Thanks for the link. I believe the additional penalties for bremsstrahlung mentioned below the table would not apply to Polywells, based on Nebels statment that alphas (and presumably other fusion product ions) bounce around some and them exit a cusp without giving up much of their energy to the plasma, like needs to occur in Tokamacs' or other ignition dependant systems.

I'm curious if anyone has actually calculated how favorable that cross-section with the alphas is, and how favorable we need the ion-electron collision coss-section to be for Polywell to work (i.e., what do the spatial/velocity distributions have to look like for gain to be, say, 10x greater than brem; then we can argue over how possible that is). Again, I'm pretty sure Rick already knows, and on the off chance he's reading it seems like something he might be able to share with violating any NDAs.

[MSimon]

People really need to read the available literature before shouting "only three neutrons!" I'm seeing this claim all over and it just isn't true.

You caught me. That's a maximum of 3 neutrons in any one experiment. Since there were four shots that produced neutrons, we are actually talking about a whopping 8 neutrons. Now that's a horse of a different color.

Well if you want to get sticky that is detected neutrons. You then have to account for detector efficiency etc. to estimate the actual number of neutrons.

[jmc]

Well the hardware is certainly cheaper.

On another note, if the collective expansion speed of the plasmoid is considerably slower than the thermal velocities of the plasma confined inside it then that would relax the densities required as the confinement time would be larger than that of an exploding pellet. The expansion force of the self-contained plasmoid after all, depends on the hoop force of its own current and might thus be decoupled from the thermal speeds of the particles inside (Any proofs handy to the contrary?)

Well, since you ask so politely:

http://en.wikipedia.org/wiki/Virial_the ... tic_fields

Thus the lifetime of a plasmoid is expected to be on the order of the acoustic (or Alfven) transit time.

Back to Focus Fusion,

What if you had a hot plasmoid core, surrounded by a cold dense plasma periphery? Could the intertia of the surrounding cold plasma, confine the hot core for timescales exceeding the ion accoustic time?

[Art Carlson]

Well the hardware is certainly cheaper.

On another note, if the collective expansion speed of the plasmoid is considerably slower than the thermal velocities of the plasma confined inside it then that would relax the densities required as the confinement time would be larger than that of an exploding pellet. The expansion force of the self-contained plasmoid after all, depends on the hoop force of its own current and might thus be decoupled from the thermal speeds of the particles inside (Any proofs handy to the contrary?)

Well, since you ask so politely:
http://en.wikipedia.org/wiki/Virial_the ... tic_fields

Thus the lifetime of a plasmoid is expected to be on the order of the acoustic (or Alfven) transit time.

Back to Focus Fusion,

What if you had a hot plasmoid core, surrounded by a cold dense plasma periphery? Could the intertia of the surrounding cold plasma, confine the hot core for timescales exceeding the ion accoustic time?

If you have an inhomogeneous plasma, then the acoustic transit time is not well defined. The exact answer is the first equation in the Wikipedia section cited. But yah, adding mass around the core will slow down the expansion.