X-ray bremsstrahlung measurements on an ECR-discharge in a magnetic mirror

The hot electron component of a microwave heated electron cyclotron resonance (ECR)-discharge is investigated. The plasma formed from different noble gases is contained in a simple magnetic mirror configuration. Improved X-ray diagnostic methods and an improved numerical deconvolution scheme are used to measure the volume bremsstrahlung spectrum emitted by the high energy electron and to derive their energy distribution function. For kinetic energies below 350 keV the electron energy distribution obeys a power law, if a cold plasma component (kT e <100 eV) is present. The density of electrons with energies above 10 keV turns out to be smaller than 10 14 m -3 . These results, together with the observed dependence of the power-law distribution function both on the pressure and on the nuclear charge number Z of the neutral gas, provide new insights into the electron acceleration and loss mechanisms of an ECR-discharge.