Gyrotron Control
A gyrotron is the high-power millimeter-wave source for electron cyclotron heating, and its operation depends on tight control of voltage, current, and field.
How it makes power
A gyrotron accelerates an electron beam into a strong magnetic field where the electrons gyrate. In a resonant cavity their gyration couples energy into an electromagnetic mode at the cyclotron frequency, producing a coherent millimeter-wave output that is coupled out through a window. Efficiency depends on the beam energy, the field, and the cavity geometry all matching the intended mode.
Controlled parameters
The main knobs are the cathode and body high voltages, which set beam energy, the beam current, and the superconducting-magnet field that fixes the operating mode. Output power is trimmed mainly through the beam voltage and current. A depressed collector recovers energy from the spent beam, and its voltage is regulated to keep efficiency high and heat load manageable.
Protection interlocks
Gyrotrons are fragile at full power. Arc detectors watch the window and cavity and crowbar the voltage in microseconds on any arc. Body current, collector temperature, cooling-water flow, and the output window temperature are all interlocked; the window in particular can fracture if it overheats, so its cooling is a protected function.
- Beam voltage and current set output power
- Superconducting magnet fixes the operating mode
- Arc detection crowbars voltage in microseconds
- Window and collector cooling are interlocked
Modulation
For real-time plasma control the output must be switched or modulated quickly. Fast on-off is done through the beam voltage or a control electrode, letting the system pulse power onto a rotating magnetic island in phase with its rotation. This demands a source that can start and stop cleanly without damaging transients. In the Kronos electron-cyclotron design model, such modulation supports island stabilization on the simulated breeder plasma.
A gyrotron is a precision instrument; its control system exists as much to keep it alive as to shape its output.