Suppose I had some plasma in box with walls that allowed nothing thru, photons, plasma, energy. Now heat the plasma and maintain some temperature T (ignore the difficulty in heating the plasma with the above walls, just assume you can). An approximation to this might be some small region of the sun at temperature T and nearly in equilibrium? I assume at constant T there is an equilibrium where just as many photons are absorbed as are emitted? How will the total kinetic energy in the plasma compare to the total energy in photons? Thanks for any help!