The use of a high-current electron beam in plasma relativistic microwave oscillators
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The Use of a HighCurrent Electron Beam in Plasma Relativistic Microwave Oscillators K. S. Bekhovskaya, I. L. Bogdankevich, P. S. Strelkov, V. P. Tarakanov, and D. K. Ul’yanov Prokhorov Institute of General Physics, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia email: [email protected] Received April 15, 2010
Abstract—Relativistic microwave electronics faces the problem of using high currents of relativistic electron beams; i.e., it is possible to use beams the current of which is lower than that of actually existing highcurrent accelerators. We show the possibility of increasing the power of radiation generated in a plasma relativistic microwave oscillator (PRMO) due to an increase in the absolute value of current. For the beam currents close to the value of limiting vacuum current, the efficiency of microwave generation decreases; therefore, we study PRMO schemes with a high value of limiting vacuum current, i.e., schemes with a small gap between a hollow relativistic electron beam and the waveguide wall. The results of the experiment and numerical simulation are discussed. DOI: 10.1134/S1063780X11070051
INTRODUCTION Relativistic microwave electronics faces the prob lem of using high currents of relativistic electron beams (REBs) at a given electron energy. For example, for an electron energy of 500 keV, it is possible to effi ciently use a current up to 5 kA in microwave oscilla tors (up to 2–3 kA in plasma relativistic microwave oscillators (PRMOs)), whereas electron accelerators give the possibility to obtain beam currents of a few tens of kiloamperes.
The aim of this work is to use another reserve for increasing the power, i.e., to work at high currents of actually existing accelerators, which cannot yet be used either in vacuum microwave oscillators or in plasma oscillators. In addition, we issue a challenge of increasing the power of microwave radiation of PRMOs due to increasing REB current with the pres ervation of the achieved efficiency and the most important property of PRMOs, i.e., the possibility of fast electronic frequency tuning severalfold. We recall
According to the analytical theory [1], a PRMO can effectively operate at currents that do not exceed a value of 0.4–0.5I0, where I0 is the limiting vacuum current [2]. This means that the design of highcurrent (for a given electron energy) microwave oscillators requires the use of a system with a high value of limit ing vacuum current. The limiting current value increases with decreasing gap between the electron beam and the waveguide wall. A smooth cylindrical waveguide with a constant diameter is used in plasma microwave oscillators, which gives a technical possi bility to make the gap between the REB and the waveguide wall small and thus to obtain a high value of limiting vacuum current. The theoretical predictions were experimentally proven. A physical experiment [2] with the injection of a hollow REB into a tubular plasma was carried out. The value of limiting vacuum current was 3.3 kA. The curren
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