[philipkglass]

They posited a clever solution for the irresistible temperatures. They didn't plan on having any structural material survive contact with with the fuel plasma. The quartz inner wall would be protected by a vortex of neon. Most energy transfer to the hydrogen propellant would be as radiated visible and UV light through the gas boundary and quartz wall. (There would also be some direct heating by neutrons.) The hydrogen propellant on the other side of the wall would be seeded with finely divided tungsten to make it absorb 98% of the radiant energy. The propellant would be much cooler than the plasma fuel, though still blazing hot [1]. The whole concept is in the intriguing fuzzy transition zone that separates AM engineering from FM [2]. It seems more likely to go "boom" than "whoosh" but I Am Not a Nuclear Rocket Scientist.

[1] https://www.osti.gov/servlets/purl/4729955

[2] Actual Machines / Fucking Magic, from the Turkey City Lexicon: https://www.sfwa.org/2009/06/18/turkey-city-lexicon-a-primer...