Noise characteristics of a plasma relativistic microwave amplifier
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MA ELECTRONICS
Noise Characteristics of a Plasma Relativistic Microwave Amplifier P. S. Strelkov, I. E. Ivanov, and D. V. Shumeiko Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia e-mail: [email protected] Received October 12, 2015
Abstract—Reasons for the occurrence of microwave noise at the output of a plasma relativistic amplifier have been analyzed. It is found that, in the absence of an input signal, the emission spectrum of the plasma relativistic microwave amplifier is similar to that of an electron beam in vacuum. It is concluded that microwave noise at the output of the amplifier appears as a result of amplification of the intrinsic noise of the electron beam. The emission characteristics of a relativistic electron beam formed in a magnetically insulated diode with an explosive emission cathode in vacuum have been studied experimentally for the first time. An important point is that, in this case, there is no virtual cathode in the drift space. DOI: 10.1134/S1063780X16070102
1. INTRODUCTION The main characteristics of plasma relativistic microwave amplifiers (PRMAs) were described in [1– 5]. Noise microwave emission was observed at frequencies close to that of the amplified microwave signal [2]. It was detected even in the absence of an input microwave signal. In [2], it was found that the noise intensity decreased with increasing input signal power. Such a decrease is caused by nonlinear competition between the intense electromagnetic field at the input signal frequency and the fields with a relatively low spectral density at other frequencies. This effect makes it possible to obtain an output microwave signal in which the power at the frequency of the amplified signal is 90% of the total power. Since the PRMA amplification band is fairly wide, the microwave noise observed in a ≈2-GHz-wide frequency band can occur due to the self-excitation of longitudinal and transverse modes of the microwave amplifier’s electrodynamic system. Another reason for the occurrence of the observed wideband microwave noise is amplification of the intrinsic microwave radiation of the relativistic electron beam (REB). This microwave radiation arises due to fluctuations of the current generated by the explosive emission cathode of the magnetically insulated diode. 2. EXPERIMENTAL SETUP Figure 1 shows the PRMA scheme. REB 1 is formed in a magnetically insulated diode. The diode consists of explosive-emission transverse-blade disc
cathode 2 [6, 7] and tube 3. Tubular REB 1 propagates along the axis of the vacuum chamber in a longitudinal magnetic field of 4.5 kG, passes through tube 5, and then falls onto collector 6. Plasma 4 is created by ionization of xenon at a pressure of 1.5×10–4 Torr with the help of an auxiliary electron beam emitted by hot annular cathode 7. Since the hot cathode is located outside tube 5, relativistic electrons do not reach the hot cathode and the plasma does not reach the magnetically insulated diode. Tubular plasma 4 is created over 100 μs, aft
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