A. Rosenberg

High‐power radio frequency generation in a hollow‐cathode discharge

High‐power rf oscillations are obtained in a resistive load installed in the external electrical circuit of a low‐pressure magnetic‐field‐free hollow‐cathode discharge. These intense rf oscillations have been shown to be due to a collisionless instability of the cathode sheath. A very simple device based on this effect is shown to serve as a convenient and powerful rf oscillator. Typical results first achieved without any optimization, for frequencies of 20–30 MHz and load resistances of several tens of ohms, are as follows: power of about 5 kW and efficiency ∼25%.

High-frequency modulation of an electron beam produced by a plasma cathode

We present a detailed study of the recently discovered modulation at frequencies of hundreds of MHz of an electron beam produced by a plasma cathode. The plasma cathode consists of a ferroelectric disk sample [BaTiO3 or Pb(Zr, Ti)O3] that is placed in a cylindrical metal box having an output window covered by a grid. The plasma is prepared by an incomplete discharge that was ignited by a few kV driving pulse applied across the ferroelectric disk. It was shown that the current modulation appears only when the driving pulse is applied to the front gridded electrode of the ferroelectric sample and the solid rear electrode is grounded. The modulation spectrum is quite narrow (⩽3%), with harmonics at frequencies up to a few GHz. The basic frequency of modulation was found to be dependent on the length of the feed cable to the sample. Investigation of the plasma and the beam modulation properties and their dependence on the experimental parameters is presented. The results indicate the formation of a plasma at ...

The Orbitron as a stimulated‐bremsstrahlung glow‐discharge maser

A new physical explanation for the operation of the Orbitron maser is presented. The Orbitron experimental results are shown to be in agreement with the prediction of the theory of amplification by stimulated emission of bremsstrahlung.

High-frequency current modulation in a diode with a plasma cathode

The authors present a study of the modulation at frequencies of hundreds of MHz of an electron beam (I/sub e//spl les/30 A, E/sub e//spl les/40 keV, /spl tau//sub p//spl les/35 /spl mu/s) produced by a plasma cathode. The plasma was prepared by a noncomplete discharge that was ignited by a driving pulse applied between the front strips and a solid rear electrode of a ferroelectric sample [BaTiO/sub 3/ or Pb(Zr,Ti)O/sub 3/]. Investigation of the plasma and the beam modulation properties and their dependence on the experimental parameters is presented. The results are discussed within the framework of electrons oscillating in the potential well created by the positively charged plasma having feedback coupling with the input cable.

Collision‐induced resonant amplification of electromagnetic waves by electrons in circular orbits

Electrons moving in circular orbits and colliding with gas atoms interact with a circular electromagnetic mode. Applying the linearized Boltzmann equation, the known nonresonant‐stimulated bremsstrahlung and the near‐resonance Landau effect are obtained. We predict that resonant electrons moving with angular velocity equal to the azimuthal phase velocity of the electromagnetic wave can exchange energy with the wave if the momentum transfer cross section for an electron‐atom collision is velocity dependent. Amplification is obtained if the momentum transfer cross section has a positive slope.