What does thermal (non-)equilbirum mean in the context of a fusion reactor (such as the Helion reactor)? A while ago, there was a question here asking about the impact of Todd Rider's thesis about various fundamental limitations to fusion reactor efficiecy. That question was mainly concerned with  why several companies even attempted aneutronic or non-thermal-equilibrium fusion reactors.
I am interested in the specific reactor approach postulated by Helion. They propose to burn D-³He fuel, which according to Rider, can yield energy if burnt in thermal equilibrium. The proposed approach uses pulsed magnetic confinement, which supposedly leads to thermal fusion.
Does the reactor approach of Helion count as maintaining a thermal-equilibrium reaction ?
 A: 
They propose to burn D-³He fuel, which according to Rider, can yield
energy if burnt in thermal equilibrium

Just barely.

Does the reactor approach of Helion count as maintaining a
thermal-equilibrium reaction ?

Yes. The plasma is thermalized in bulk during the reaction time. The reactions will mostly take place during the brief period of maximum compression. The now-hot(ter) plasma then relaxes against the field for energy recovery.
This is similar to a car's engine, where the reaction is fired somewhere near the top-dead-center and then allowed to expand against the piston (at a much slower rate) for power recovery. If you look at one entire cycle of the engine you would be confused why it is considered thermal, but if you consider just the period of the reaction is clearly is.
Rider's work involving non-thermal plasmas is referring to devices like the fusor, where the ions have a non-thermal distribution and the reactions take place between these particles. These are vanishing in the thermal case.
Two things to note:

*

*The otherwise similar-looking TAE device is a non-thermal FRC system (or at least it was, when proposed).


*The Helion design does not aim to have appreciable fusion burn, their proposed levels of fusion are not unlike existing older devices like JET. The entire concept hinges on the power recovery system, which they claim will allow them to produce net energy even operating below Q = 1.
