mvanwink5 wrote: ↑Thu Mar 07, 2024 2:47 am
Ions & electrons don't thermalize in a pulse operation which is a big point in a pulse operation and improves direct magnetic recovery efficiency. Quartz is transparent to UV, but I do not know how much of the X-rays will pass, quartz is certainly not opaque to X-rays though and the tube is not that thick judging by the pictures. Quantitative details of energy transfer are important as opposed to hand waving. Are we only able to guess? I had thought Helion said they had over all 95% efficiency fusion energy to electric (presumably for best fuel cycles). SJ?
Ions and electrons start out at a pretty high difference in temperature. That is mainly the result of the acceleration and merging process.
Helion talks about a Te:Ti of 0.1 in their recent paper, but results from Trenta released earlier show an even lower ratio (~0.06) for some of the pulses.
So I assume that 0.1 is conservative.
Over the length of the pulse and especially during the compression phase ions and electrons move closer to equilibrium. My estimate is that starting from a Te:Ti of 0.1, the ratio would not exceed 0.2 over the 1ms pulse length. It could be a lot less and again the 0.1 seems conservative given the results from Trenta.
X-ray absorption into the quartz tube is indeed a thing. They typically deposit the most in the first mm of the thickness of the 5mm thick tube. There is however a soft gradient within the material. So, the is no sharp terminator and that reduces stresses on the material.
As for the conversion efficiency: The 95% refers to the efficiency of the input energy recovery. The fusion energy recovery is somewhat less efficient because of neutrons, X-rays, transport and other losses. Though some of them might be recoverable by other means, at least to some extent.
This was occasionally mentioned in passing. E.g. David Kirtley said in his talk at Princeton that assuming all losses are actual losses in a pulsed system is a "bad assumption to make". I am not sure how to interpret that exactly.
There are also other aspects that come into play. E.g. over the length of the pulse, the FRC will lose particles. So the longer the pulse, the lower the recovery efficiency and fusion rates drop as well. They will have to find the optimal balance.
Helion still keeps that aspect of their design pretty close to their chest and even I don't know everything. I think that they want to see how well all of this works out in Polaris before they talk about it in more detail (if they don't want to keep it a trade secret).