Magnetothermodynamics: Measurements of the thermodynamic properties in a relaxed magnetohydrodynamic plasma.

We have explored the thermodynamics of compressed magnetized plasmas in laboratory experiments and we call these studies "magnetothermodynamics". The experiments are carried out in the Swarthmore Spheromak eXperiment device. In this device, a magnetized plasma source is located at one end and at the other end, a closed conducting can is installed. We generate parcels of magnetized plasma and observe their compression against the end wall of the conducting cylinder. The plasma parameters such as plasma density, temperature, and magnetic field are measured during compression using HeNe laser interferometry, ion Doppler spectroscopy and a linear $\dot{B}$ probe array, respectively. To identify the instances of ion heating during compression, a PV diagram is constructed using measured density, temperature, and a proxy for the volume of the magnetized plasma. Different equations of state are analyzed to evaluate the adiabatic nature of the compressed plasma. A 3D resistive magnetohydrodynamic code (NIMROD) is employed to simulate the twisted Taylor states and show stagnation against the end wall of the closed conducting can. The simulation results are consistent to what we observe in our experiments.