Fighting the Early Beams

Our research team is continuing to examine the causes of the shot-to-shot variability that affects FF-1 (as it does all DPFs to date) and the reason that we, in general, are getting lower fusion yields than our theory expects. Previously we have traced this to a too-early generation of the electron and ion beams that drain energy from the plasmoid before it has time to fully contract, limiting the density of the plasmoid and thus the rate of fusion reactions.

In the past month, we’ve analyzed a number of shots that show clearly that this first early beam is much “softer”, having less energy per particle than the second beam which is more closely coincident with the neutrons from the fusion reactions. Our literature search did turn up two other mentions of this early-soft-beam phenomenon, one in 1998 and the other in 2008.

In addition, our ICCD images have shown considerably broader sheath currents with less clear filamentation than in some images taken from shots at higher fusion yields. A broad sheath and fuzzier filaments can lead to early beam formation when oversized filaments collide with each other and the pinch is still somewhat broad. Tight filaments by contrast don’t coalesce until a very tight pinch has formed. Again, there is a lot of discussion of broad sheaths in the literature.

We now are tracking down possible causes of the broad sheath and ways to fix it with different operating conditions.

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