Investigation of the density and temperature of electrons in a compact 2.45 GHz electron cyclotron resonance ion source plasma by X-ray measurements

X-ray measurements of the plasma of a compact 2.45 GHz electron cyclotron resonance ion source (ECRIS) are performed to determine the temperature and density of the electrons heated resonantly in the ECRIS. The x-ray detector used to investigate the plasma consists of a small silicon (Si-PIN) photodiode to detect photons in the energy range of 1-100 keV. The detector has an energy resolution of 180 eV at 5.9 keV that allows us to record detailed x-ray spectra. Assuming two temperature electron populations, both Maxwellian distributed, the analysis of the x-ray spectra shows a temperature of about 2 keV for the hot electron fraction in addition to the population of cold electrons at less than 2 eV. The fraction of the hot electrons amounts to 1-10%. We present a description of the x-ray detector set-up as well as x-ray spectra and calculations for the temperature and density of the electrons in the ECRIS plasma.