High-frequency electron beam modulation by a ferroelectric cathode with anomalous plasma resistance

Abstract

Spectroscopic measurements are reported of the plasma formed inside a cathode having a ferroelectric source incorporated in it. These measurements were performed during the generation of a high-frequency modulated electron beam in a planar diode with the above cathode. It was found that there is a spatially periodic structure in the plasma density, electric field, and electron energy in the plasma in the longitudinal direction from the ferroelectric surface. The plasma density, electric field, and electron energy vary in the range of 5×1013–5×1014 cm−3, 0–1 kV/cm, and 2–30 eV, respectively. Also, it was found that the plasma electron temperature is ∼8 eV in the vicinity of the ferroelectric surface and ∼2 eV in the bulk of the plasma. To explain the obtained experimental data a qualitative model is suggested. The model is based on fast periodic appearance of anomalous plasma resistance due to generation of ion-acoustic instability. The latter is controlled by the ratio between the velocities of the current carrying electrons and the ion sound. Computer simulations show good agreement with the experimentally obtained data.