Observations and modeling of the electron cyclotron emission background in the Levitated Dipole Experiment

Abstract

Hot electron cyclotron emission (ECE) measurements and modeling calculations have been carried out for the Levitated Dipole Experiment (LDX)5. Heterodyne radiometers at 110, 137 and 165 GHz have been used to view the plasma from bottom and midplane locations. An intense environment of harmonic ECE of up to 1 keV at 110 GHz and afterglow decay times of up to 6.9 seconds were observed at lower pressures. Interpretation of the emission levels in terms of hot electron parameters requires integrating modeled emission over a large magnetic field range of 0.09 to 3.2 Tesla and a k to B angular view range of 0 to 90° within the field of view of each receiver as the hot electron density peak is followed around a given flux contour. Hot electron temperatures of the order of 100 keV, depending on knowledge of the electron density peak location, were determined by taking the ratio of radiometer signals at different frequencies. Abrupt radial movements of the highly peaked hot electron density where evident, particularly with ECRH turn on and turn off. © 2010 IOP Publishing Ltd.