rnebel wrote:JMC and MSimon:
However, the wiffleball mode is essential and the ion convergence simply makes things better. If we can’t get the wiffleball, then we can kiss our behinds goodbye. That’s why we are focused on achieving the wiffleball and we aren’t paying any attention to Rider and Nevins. They’re just a distraction. Does this kind of make sense?
Yes, it makes perfect sense to start with the biggest challenge and then try to enhance the device from there. I have, infact done some handywavy calculations myself that suggest that an isotropic plasma in an open box design would probably get beyond breakeven with 8 point cusps (diameter 2m, field 1 Tesla) or so (I'm not sure whether it would still be the case with line cusps and funny cusps though)
How is the wiffleball thing going? I was told by a former EMC^2 researcher that in WB4 any attempt at wiffle ball formation in steady state mode while he was working there, invariably led to well blowout. He attributed it to an uncontrollable increase in density which resulted in a current to the magrid that was too great for the power supplies to cope with.
If stable wiffleball formation is a problem then it might be interesting to just try and achieve a stable wiffleball at a few hundred volts rather that 10KV, leave fusion to the side for awhile and see how high you can push up the density. At lower voltages your magrid might be able to handle higher currents for longer.
I was also wondering what would happen if instead of fuelling the device through gas breakdown, the device was fuelled by exploding a pellet in the centre. When gas breaks down throughout the device I imagine the electrons would hug onto the magnetic fieldlines where they were first ionized throughout the device, but if a pellet exploded in the centre they would push back the magnetic fieldlines as the cloud expanded. If you weren’t focussed on making fusion maybe you could use a small pellet of water ice or something easier to handle then cryogenic deuterium. And if the final temperature was to be 100eV then perhaps the energy required to explode a small pellet would not be prohibitive.
I can imagine that the WB6 pulsed mode might have achieved wiffle ball formation, if the thermionic emitters were bang on the cusps then the electron from them would only ionize the gas in the low field centre maybe then the ions formed in this low field region, pushed back the field enabling the plasma to swallow up yet more gas, ionizing it and forming a wiffleball.
Another way of obtaining the wiffleball might be to start with no field, or a very weak field, an ionize the gas in this state and then slowly increase the field while the gas is already ionized, the new field lines from the increasing magrid current will not penetrate the plasma on timescale below the resistive time.
Perhaps it was the effect of pushing the plasma out of the field by alternating the octahedral and truncated cube formations that allowed Keller and Jones in their 1966 Laussane paper to achieve good plasma confinements in their Polyhedral magnetic field configuration (albeit at 7eV).
I still prefer exploding the pellet though, it will allow you to control the precise quantity of material that goes into the plasma, push back the fieldlines and lower the neutral density in the tank outside the plasma which will in turn reduce charge exchange losses.