The problem with scalability seems to be the properties of the materials being used to generate necessary field strengths, currents, etc. The size is critical because the fuel ions must be zipping around at a minimum energy to generate fusion reactions. A minimum field strength is required to create the potential well to attract the ions and impart them with high velocity. To create the minimum field strength requires a minimum electric current in the electromagnet coils, and the wire coils must therefore have a minimum cross-sectional area to carry sufficient current, otherwise they will heat up and burn out, like the filament in a light bulb. Bussard's test reactor ran in pulsed mode to prevent overheating

Even if they don't burn out, for steady-state operation they have to be cooled to maintain field strength and coil geometry, hence the need for an integrated active cooling system. At the sizes required for a cooling system to be integrated, the copper coils need to be 1.5 meters in radius, and this happens to be the minimum size for superconducting magnets with internal cooling. And superconducting magnets are a better choice than copper anyway because they have higher field strength. So, it's luck that nature provides materials that don't require magnets the size of a mountain to achieve this. They are still big though, and the cost still substantial. (I hope I understand this correctly)

Other than that, the main problem seemed to be balancing the power production versus the power losses, with the latter causing the biggest headache. Bussard claims to have solved this problem with his latest wiffle ball reactor (WB-6). He completely eliminated sharp edges that generated high local electric fields, exposed metal that absorbed free electrons, and support structure that blocked magnetic field lines, and that sapped the system of free electrons needed to maintain the high negative potential. That's why it looks so cool (engineering wisdom).

Issues I have include:

- Bussard's experiments so far have used D-D fusion, not p-B11 fusion as he recommends. Will his results be comparable with p-B11? Will there be additional problems with this fuel that should be solved with a small pulsed reactor? Why did he use D-D fusions in the first place since it's harder to detect neutrons than helium ions, unless I am mistaken. If he aims to use p-B11 as a fuel in the full-scale reactor, he should have demonstrated experimental similarity with the pulsed reactor using p-B11.

- Gas pressure outside the reactor has to be much lower than inside to prevent arcing between the reactor and exterior structures. I found no explanation in his paper as to how he was going to produce this pressure difference. He simply characterized it mathematically without any engineering description. The ions inside the reaction zone would provide a much higher gas pressure than the vacuum outside, but there was no indication of how he intended to control this aspect. Safety might be an issue here.

- Why didn't he seek funding from the DOE instead of google? Is it because he wants to patent his work and the DOE wouldn't let him? That would seem to be a bit selfish for a man 78 years old. How long would he benefit from a patent? Wouldn't a patent prevent anyone else from benefiting for 20 years hence? Are the patents held by him, or by an estate? Legal rights seem to be clouding the issue, and maybe even slowing progress.

Overall, I'm not a physicist, so what the hell do I know!