"I'm skeptical of the Bremmsstralung and synchrotron radiation losses"

It's a chellenge for p-B11, but it can probably be controlled by manipulating anode height and fuiel mixture.

"Even at the levels extrapolated by Bussard the net power produced by his Polywell reactor would be only a few percent above input power. Any significant powerplant would have to be gigantic."

Actually, a Polywell would only have to be about 1.5M in diameter to produce about 100MW net power (at about 5MW input).

"So far nothing has been stated by the researchers (Nebel et al?) that would indicate these losses would go away if it were scaled up."

Bussard believed losses scaled at about r^2, while power scales at about r^7 (or B^4*r^3).

We'll have a better idea soon. The just-approved WB-8 has 8 times more powerful magnets. Scaling from .002 watts output to 8 watts should tell us a lot.