X-Ray Measurements of the Levitated Dipole

Initial plasma experiments in the Levitated Dipole Experiment focus on producing hot electron, high beta plasmas using a supported dipole configuration. Plasmas were created using multifrequency ECRH, and we find that most of the plasma energy is stored in the fast electrons, $T_e \sim$ 50 keV. The energy spectrum of the x-ray emission below 740 keV is measured by a four channel pulse height analyzer using CZT detectors. Temporal resolution is achieved by collecting multiple spectra during each shot. The electron temperature is inferred from the x-ray energy. A hard x-ray camera\footnote[2]{S. von Goeler et. al. Rev. Sci. Instrum. \begin{bf}65\end{bf}, 1621 (1994).} is used to view the spatial distribution of x-ray intensity in the plasma at a maximum of 60 fields per second. In addition, a single NaI detector (which views energies up to 3 MeV) measures the temporal fluctuations of x-ray emission from the plasma. X-ray measurements have shown the profile changes resulting from various ECRH configurations, and they are used with other diagnostics to determine plasma profiles and parameters.