Reply To: Repowering the electric utility industry

[asymmetric_implosion]

The temperature that seemed optimum for us was around 300 C. I don’t know the exact cause but I speculate it has to do with the local gas pressure changing the mass carried by the plasma. Our anode heats due to repetition rate. When it is cold, the implosion time (time between current start and minimum in the dI/dt) is ~700 ns. As the run progresses to steady state, the implosion time drops to ~550 ns. At 550 ns, the neutron yield is optimized. Even at the optimum implosion time, the hot anode performed better than a cold anode.

It is important to note that we use SS304 as the anode. SS304 has poor thermal conductivity. We used emission spectroscopy to look for impurities and found none. I want to do a scan with a mass spec on the fuel gas after the run but it’s not in the cards right now. When we switched to a Moly anode, we noticed a drop in yield of a factor of two. Moly has a thermal conductivity about 1/4 copper. We know from measurements that the SS304 has a large temperature gradient relative to Moly. Is that gradient important? Don’t know. We know that all metals take up deuterium to some extent. We fired a number of shots on an anode in deuterium and then switched to argon. We recorded neutrons during the argon run. The temperature might be the optimum to release hydrogen from the metal and allow it to be replaced with D2. Over several runs you go into saturation. Burns reported a similar hypothesis on DT shots. It is hard to see the difference between H2, D2 and T2 using spectroscopy. We’ve found that operating at 300 C is difficult with Moly because it is nearly isothermal and our o-rings suffer from the temperature. Therefore, we actively cool the anode. In the process, our yield went down. The parameter space grows more complex as the temperature increases because the chemistry of the electrodes and possibly the chamber walls becomes important. These are problems addressed in plasma reactors for deposition and etching but they are seldom thought about in the context of a PF. You mentioned sulfur in SS304 in a past conversation…we see no evidence of sulfur. Based upon conversations related to other work, sulfur is just a bad in copper as SS304. In our experiments, the most likely contamination comes from the vaporization of anode metal. The cloud of vapor expands from the anode base and into the pinch region. Is some tiny mass present before the next shot that enhances the neutron yield as is described in lit with high Z noble gases. I know in our experiments with fuel mixing that we could not see any lines of argon additive at the optimum neutron enhancement. The same could be true for Fe, Moly or tungsten. The metal should plate out so I wouldn’t expect you to see this effect firing a few shots an hour or day. It might be that the vaporized metal releases the impurities trapped in it. Our solution to volatile products is a low base vacuum. We don’t start operating until our base vacuum is ~1E-6 Torr. The machine works better at base pressures of ~5E-7 Torr.