Who knows, but using money scaling, instead of $40 million per year, you use $4 million per year (close to EMC2's budget), then direct scaling would suggest a time frame of ~ 50 years.
I would have preferred a budget close to Bussard's desire, though more intermediate steps (like a 1/2 scale machine, and multiple geometry modifications. A parellel process of multiple machines, perhaps at various labs, to not only pin down the physics, but to also address many engineering issues. Perhaps a program of $500 million over 10 years . Alas, nobody asked for my openion.
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Size scaling indeed is limited for FF , as well as FRC. Power outputs of ~ 5-10 MW per unit seems to be the sweet spot. Polywell seems to be open ended, at least till things start melting. Using multiple units might compensate some, especially for FF as it seems to be the most compact, but there are limits. I think a FF might be ideal for powering a space thruster where not much acceleration/sec. is needed, but for a booster/ take off from Earth, nothing would beat a Polywell. Perhaps as important, the waste heat handling in a space craft might also favor the Polywell, at least if the Polywell can reach P-B11 Q's of ~ 20 while FF and FRC is limited to Q's of ~ 3-5. If all of your input energy ends up as waste heat, and ~ 80% of the fusion energy can be converted to useful energy, without the need for secondary waste heat management the Q advantage of the Polywell would be tremendous. In space the waste heat has to be disposed of with radiators, and this incurs a significant weight penalty, which means you need more power for the same acceleration, which means more waste heat to handle, which means more weight, which means.....
Dan Tibbets
