OK, here is Bussard's take on brem, via Ligon (from Simon's post):
Objection 3, bremsstrahlung radiation, is a very complex subject. The essence is that high-velocity electrons, at high density, especially in the presence of ions that have a lot of electrical charge on their nuclei, will cause the electrons to lose energy in the form of x-rays. This objection is not a serious problem for deuterium and deuterium-tritium fuel systems, even according to the critics. The objection does apply to p-B11, which requires much more severe conditions to cause fusion.
Here, we might even extend the analogy to the diesel engine. Diesel fuel is terribly prone to being ignited by the heat of compression, and will cause premature detonation if burned in a spark ignition engine. Alcohol is very resistant to this phenomenon, and gasoline is relatively resistant to it. In fact, diesel engines don't even have spark plugs, they control ignition by injecting the fuel once the compression stroke is completed. Overall, the Otto and Diesel cycles are very similar, but the more "exotic" fuel requires special measures to achieve proper operation. But diesels are desirable because they can operate at higher pressure, and so more efficiently, than the spark ignition fuels, and the fuel, at least in the early days, was cheaper.
The first way in which the bremsstrahlung problem is mitigated is a natural process of the machine itself. The electrons that form the potential well are at very high energy at the outer boundaries of the machine, but their density is lower there. In the center, where their density is high, they have given up most of their kinetic energy in the process of creating the potential well that drives the fusion reaction. Still, the ions are at their most energetic in the center of the machine, so the objection has been raised that they will "heat" the electrons and make them produce bremsstrahlung. The machine has its own mechanism for correcting this, a process similar to the edge-annealing process, based again on the Electrodynamic nature of the machine. The electrons never spend very long in the center of the machine, so they limit the amount of energy they can pick up there, and they tend to lose that energy back to the ions at the outer edge where that annealing is going on. In addition, the "virtual anode height" in the center of the machine is a function of ion density there, and it can be manipulated to reduce the problem (this might be seen as analogous to changing compression ratio of a spark ignition engine to control detonation). Finally, control of the relative abundance of hydrogen and boron can be used to mitigate the problem. Using all three together, Dr. Bussard predicts that bremsstrahlung can be reduced to easily manageable levels.
http://www.classicalvalues.com/archives ... d_u_1.html
Nebel mentions the thermalization problem in the MSNBC Cosmic Log thread, and alludes to his own POPS research in asserting the belief that ways can be found to "innovate around it."
http://cosmiclog.msnbc.msn.com/archive/ ... 66532.aspx
Later in the thread he also makes an interesting point about parabolic wells giving surprisingly different results than square wells.