X-ray measurements of electron density and temperature in the PFRC-2

The Princeton Field-Reversed Configuration-2 (PFRC-2) is an FRC heating and confinement experiment. FRC plasmas are formed and heated by odd-parity rotating magnetic fields (RMF_o). X-rays emitted via Bremsstrahlung from PFRC-2 plasma are of interest in order to measure electron energy distribution functions (EEDFs) from which electron number density n_e and temperature T_e can be extracted. Three Silicon Drift Detector (SDD) x-ray pulse-height detectors in the center cell measure the Bremsstrahlung emissions above 150 eV from three viewing chords, where two are near the central plane and the third is near the nozzle. We describe x-ray measurements of the PFRC-2 experiment both in the case where RMF is applied, resulting in an FRC, and in the case where RMF is not applied, which results in a quasi-Maxwellian tenuous plasma (n_e < 10⁹/cc) with effective temperatures reaching 1500 eV. For the FRC plasma, x-ray measurements have been conducted at 4.3 MHz RMF frequency, 70 - 100 kW RMF power, and 300 G vacuum field. Machine updates are in progress to lower RMF frequency to 2 MHz and increase magnetic field to 800 G in order to directly heat ions using RMF_o. X-ray measurements for this new regime will also be discussed.