Reply To: Great News!

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asymmetric_implosion wrote: Pinch/plasmoid break up is being neglected. The e-beam can escape the pinch during breakup of the plasmoid. The damage can be substantial and it might be even worse if the electrons are high energy. You can superheat a larger volume of metal and erode more mass. It might be possible to reduce the beam current but eliminating it will be a problem. I believe the e-beam confinement by the LPP model is due to extremely large magnetic fields in a toroidal geometry. This works well until the plasmoid falls apart. Then you have hot electrons running around everywhere.

200 Hz operation is problematic for many reasons. We are finding that operating above 5 Hz is not intuitive as it was up to 5 Hz. We are thermally managing a Mo anode to control the temperature, but temperature control alone is not enough. The e-beam erosion can do two things: release gases trapped in the metal like hydrogen, oxygen and other common gases, erode the anode material into a vapor that cannot plate out before the next shot. High Z vapor like tungsten or Molybdenum seems to help the neutron yield as was reported for high Z inert gas/deuterium mixes. The current thinking on our experiment is at high repetition rate the vapor density is beyond the optimum mixing ratio which depresses the fusion yield. LPP might be able to push beyond 5 Hz if the e-beam is suppressed but plasma erosion will eventually supply enough material corrupt the gas and spoil the fusion gain. Flowing the gas a modest rates is not enough to maintain a clean environment. Even the lithography folks operating at 80 Hz had some problems with this. The solution they found was to increase the anode size above the optimum and operate with reduced yield. If I understand LPP’s operating regime, it relies on small anode diameters and high pressure. Increasing the anode size for a fixed current requires operating at lower pressure. The problem is somewhat constrained due to the PF physics.

Relying on governments to get this working is a joke. Resources are key and private resources would be better suited to drive this forward. I don’t know if a global collaboration will come to pass if successful, but the problems are materials limited. All fusion concepts have materials problems and they are not addressed because most fusion folks have a plasma background rather than a materials background. I agree that more can be done but materials are going to be a limiting factor in any fusion device. I’ve done a small materials survey and no material I’ve run across can withstand the e-beam and/or plasma erosion without sacrificing grams of material for the 1E7 shot operation at 100 Hz and 60 kA.

So electrode erosion is a show stopper…

The question is: how long can one electrode be used? How many shots? 200 Hz -> 120 * 10⁶ shots per week. So one electrode needs to last at last 120 Million shots!