Experimental study of high-frequency oscillations and forming of energy spectrum of electrons in the plasma of Penning discharge with a thermocathode

Spatial distribution of HF oscillations intensity and statial evolution of electron energy spectrum has been experimentally studied. Calculated and experimentally observed coordinates of HF oscillations intensity maximum and half-width of their existence region have been compared on the basis of the notion on electron beam interaction with inhomogeneouos plasma. The pursued investigations show that a group of intensive oscillations having frequencies close to the electron plasma frequence is present in the spectrum of oscillations excited in Penning discharge plasma. It has been disclosed that these oscillations are concentrated within the limits of primary electron beam and are accurately localized in the near-cathode plasma region. It has been ascertained that the formation of electron energy spectrum takes place in HF field localization region. It is emphasized that oscillations localization observed in the experiments, that is the distance from the cathode on which oscillation intensity maximum is observed as well as the half-width of oscillations growing region can be sufficiently well explained exactly by the presence of plasma density inhomogeneity, primary electrons beam interacts with. The conclusion is made that such mechanism of oscillations localization is typical of the majority of gas-discharged plasma-beam systems because they always have the region of density inhomogeneous plasma adjoining the electron emitter. The excitation of oscillations and the formation of energy spectrum in the direct discharge and Penning discharge with thermocathode are of the same character