Ion and Electron Flow in Hot-Cathode PIG Sources for Multiply Charged Heavy Ions

Calorimetric measurements of the power dissipated at both the anode and the anticathode of a hot-cathode Penning ion source have been made. The analysis leads to the existence of a considerable electron flow from the PIG plasma onto the cathodes. That is in agreement with the electron currents extracted through holes in the cathodes of a hot-cathode PIG source. Neither the measured plasma electron temperature of < 15 eV nor the emission of electrons from the cathodes with velocities > 0 provide an explanation. Therefore, it is assumed that a fraction of primary electrons is heated by means of nonlinear collective plasma processes. A PIG discharge model involving a peculiar velocity distribution of the ionizing electrons is presented.