High-Voltage sources for power control of gyrotrons Contact: P. Brand
The gyrotron is a source for high power electromagnetic radiation in the
millimeterwave range. The principle of operation founds on the interaction
of a beam of low relativistic gyrating electrons with the electromagnetic
field of a quasi-optical resonator. The efficiency of converting electron
beam power into microwave beam power depends sensitively on the accuracy
of the guiding magnetic field as well as on the precision of the
acceleration voltage for the electron beam. The output power of the
gyrotron can be controlled in a certain range by variation of the
acceleration voltage.
An application for gyrotrons is heating of plasmas in fusion devices by
electron cyclotron resonance absorption. Control of gyrotron output power
offers the tailoring of the heating profile as well as the generation of
heat waves for analysis of heat conductivity. A high-voltage source for
these applications is realized as a HV-OpAmp in a feed back loop for
control of the acceleration voltage in the range of 50kV to 80 kV with a
slew rate of 600 V/μs. This amplifier is realized in hybrid
semiconductor- tube technology.
Due to the high accuracy of the geometry of the gyrotron resonator and
mode converter for gaussian microwave beam generation, an erosion of
this internal tube structure by tube arcing must be minimized. For this
reason a fast switch-off of the high voltage source some μs after
event of arcing is initiated by crowbar with a multistage thyratron.
