Gyrotron

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Multiple gyrotrons

The gyrotron (short for gyromonotron ) is currently (2007) the most powerful microwave oscillator. It is based on the principle of electron cyclotron maser instability and is a combination of drift tube and cyclotron resonance - Maser . Gyrotrons work effectively in the frequency range from 5 GHz to 170 GHz with output powers of up to a few megawatts. When operated on a harmonic, microwaves in the watt range up to one terahertz can be generated. There are conventional gyrotrons, coaxial gyrotrons, and tunable gyrotrons.

They are used e.g. B. at 30 GHz in the materials processing for sintering of ceramics, at 95 GHz in the Active Denial System , or at 100 GHz 140 GHz (in the area of electron cyclotron frequency , therefore, electron cyclotron resonance heating (ECRH)) and services to 1 megawatt for microwave heating of plasmas in nuclear fusion reactors (e.g. at the Max Planck Institute for Plasma Physics or at the TCV ).

construction

Section through a gyrotron

A gyrotron consists of an electron gun, an electron compression zone, an interaction space (microwave cavity resonator ), a quasi-optical mode converter, an electron collector (collector), a high-frequency output window, the tube housing and magnets.

function

In a gyrotron an electron beam of relativistic speed is first generated. At the same time, the electrons are already passing through a magnetic field there. This causes the electrons to move on helical paths within the beam. The electron beam enters the cavity resonator, which is in an axial magnetic field. Because of the cyclotron resonance, it interacts with a part of the microwave power that is returned. Now the relativistic increase in mass comes into play: Depending on the phase position in which the electrons are on their helical orbit relative to the alternating electric field, they are partly accelerated and partly decelerated on this; Electrons rotating with a larger radius (i.e. faster) experience a slowdown in their axial velocity due to the increase in mass, they are overtaken by the electrons rotating with a smaller radius (slower) and phase synchronization occurs. Now the electrons further back in the resonator can continuously transfer energy to the electric alternating field of the microwaves. The microwaves get out of the vacuum apparatus through a window, while the processed electrons are caught on a positively charged metal wall (tube).

literature

  • CJ Edgcombe: Gyrotron Oscillators: Their Principles and Practice ; 1993
  • Machavaram V. Kartikeyan et al. a .: Gyrotrons: High-Power Microwave and Millimeter Wave Technology ; 2004

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