I have wondered howmuch hardware Tri- Alpha has built, as opposed to computer modeling. This shows that they at least have a reactor that is capable of producing a few measurable P-B11 fusion events.

The resance peak at ~ 600 KeV is consistant with published cross sections=

http://iec.neep.wisc.edu/operation.php
The information is confusing about the energy of the two alphas from the excited Beryllium 8, and the C12 breakdown that also produces one of the alphas is barely mentioned except for one graphic, which is interesting as it seems to show the third alpha as having lower energy (?).

The point of only a few energy ranges needing to be accommodated reenforces what has already been stressed for direct conversion. Compared to D-D fusion with outcomes of a high energy pr oton, tritium, He3 at different energies is more challenging to convert,and this at most accounts for ~ 50% of the aviable energy- the rest is carried by a neutron).

The target of 600 KeV for center of mass energies to produce the most fusion, may not reflect the best target. Since this is a peak, it means the cross section is leveling off, which means little gain in this area. The Bremsstruhlung radiation continues to rise exponentially, so actual gain may be negative. This may be reflected by Bussard's target of ~ 400 KeV center of mass kinetic energy target. It is on the steep up slope of the fusion cross section curve, and the Bremsstruhlung is less (perhaps ~ 40% as much. There is some sweet spot where the two competing effects has the most beneficial solution.

I, of course, hope that the plasma thermalization can be controlled to such an extent that the resonance peak at ~ 120 KeV can be used. Almost as much fusion (fusion numbers multiplied by the difference between the fuel KE, and the fusion products KE) and only ~ 10% as much Bremsstruhlung.

As a side point, This Bremsstruhlung vs the fusion cross section slope is why ideas of pushing D-D fusion up to ~ 1 MeV is counter productive. The fusion cross section slope is increasing , but at a shallow angle, while the Bremsstruhlung continues to also increase at an exponential rate (~T^1.75). There is also a sweat spot for this reaction, which according to Bussard seems to be at ~ 80-100 KeV.

Note that the MFP at the working densities and energies and machine radius is also an important considerations if annealing is considered in The Polywell.

Dan Tibbets