[pfdietz]

"Granted, if aneutronic fusion becomes possible (no time soon, even experimentally with a surplus of energy) that will be a miracle."

A group at Princeton has a concept for a FRC-based reactor burning D-3He that, through a combination of quite interesting tricks, reduces the fraction of power output in neutrons to as little as 0.5%. The design is also very small, with a power output of 1 MW. At this level of neutron output the reactor structure are lifetime components, with no replacement needed due to neutron damage. Power density is still a struggle, although the small size of the reactor helps there.

The downside (assuming the aggressive plasma physics doesn't disappoint) is where do you get the 3He.

At this point, my default vision of the future is neither fission nor fusion, but rather renewables and storage. The engineering and economic issues of these appear much more tractable. Simply extrapolating solar down its demonstrated experience curve puts the cost of PV electricity at $0.01/kWh or less when fully scaled out.

[DennisP]

I was only aware of Helion doing D-3He, and they're in Washington. Do you have a link for the Princeton group?

[pfdietz]

https://en.wikipedia.org/wiki/Princeton_field-reversed_confi...

The small company proposing using this for a notional Pluto orbiter:

http://www.psatellite.com/

Primary patent for the reactor:

http://www.freepatentsonline.com/9767925.html

[dkirtley]

Sam Cohen’s Rotating Magnetic Field experiments have shown higher temperature and reasonably long-lived FRCs. His vision is steady operating, 3He systems, atleast at first targeting propulsion. As you dial up the Helium percentages, the neutron output goes down, though the required ion temperature goes up. Princeton Satellite Systems has several NASA programs looking at the propulsion applications.

[pfdietz]

"required ion temperature"

The scheme involves significantly non-maxwellian ion distributions, so "temperature" isn't really appropriate. In particular, 3He ions get pumped to higher energy than D ions, which helps suppress DD fusion. They claim the scheme is consistent with Rider's limits on energy circulation in non-maxwellian plasmas.