Most mainstream physicists believe that the polywell design cannot work due to bremsstrahlung and electron cusp losses, as described by Rider. [0] Bussard and some of his followers have argued against some assumptions made in the Rider paper, but as far as I know, no one has found any loopholes big enough to allow a practical, power-producing reactor.

If you're interested in alternative fusion reactor designs, though, you might want to look into the levitated dipole. [1] There is a lot of evidence suggesting that this design avoids most of the major problems that plague tokamak development. [2][3] The remaining obstacles (as far as I can tell, mainly interchange instabilities and engineering difficulties) don't seem insurmountable to me. MIT made a serious attempt to build a levitated dipole reactor in the late 2000's, but unfortunately, the US Department of Energy cut off all funding in 2011.

[0] http://fsl.npre.illinois.edu/IEC/Rider,%20Phys.ofPlasmas1995...

[1] https://en.wikipedia.org/wiki/Levitated_dipole

[2] https://pdfs.semanticscholar.org/92cb/3e1ec34a707b2920f1c03a...

[3] https://dspace.mit.edu/bitstream/handle/1721.1/95395/99ja014...

I've been occasionally following the team that continued Bussard's work and they claim they can prove they can make it work in a couple years for a few million or something.

Interview with the project lead: https://www.thefusionpodcast.com/itunes/2018/8/27/dr-jaeyoun...