Magnetothermodynamics: An experimental study of the equations of state applicable to a magnetized plasma

Measuring the equations of state of a compressed magnetized plasma is important both for advancing fusion experiments and understanding natural systems such as stellar winds. In this talk, I will present results from our recent experiments on the thermodynamics of compressed magnetized plasmas^1,2; we call these studies "magnetothermodynamics". In these experiments, we generate parcels of relaxed, magnetized plasma at one end of the linear SSX device and observe their compression in a closed conducting boundary installed at the other end. Plasma parameters are measured during compression. The instances of ion heating during compression are identified by constructing a PV diagram using measured density, temperature, and volume of the magnetized plasma. Theoretically predicted MHD and double adiabatic (CGL) equations of state are compared to experimental measurements to estimate the adiabatic nature of the compressed plasma. Since our magnetized plasmas relax to an equilibrium described by magnetohydrodynamics³, one might expect their thermodynamics to be governed by the corresponding equation of state. However, we find that the magnetohydrodynamic equation of state is not supported by our data. Our results are more consistent with the parallel CGL equation of state suggesting that our weakly collisional plasmas have most of their proton energy in the parallel direction to the magnetic field.

¹Kaur et. al., Phys. Rev. E. 97, 011202 (2018).
²Kaur et. al., J. Plasma. Phys. 84, 905840114 (2018).
³Gray et. al., Phys. Rev. Lett. 110, 085002 (2013).