RF Generation Methods for Linear Accelerators

Klystron (Amplifier)

Electrons
E-field oscillation
RF signal

Magnetron (Oscillator)

Electron cloud
E-field (radial)
B-field (⊙ into page)

How RF Generation Works

Klystron

  • Type: RF Amplifier (requires input signal)
  • Electron beam: Linear, velocity-modulated into bunches
  • Buncher cavity: Input RF creates oscillating E-field, modulates electron velocity
  • Drift space: Fast electrons catch slow ones → bunching
  • Catcher cavity: Bunched electrons transfer energy → amplified RF output
  • Gain: 30-60 dB amplification
  • Clinical use: High-energy linacs (≥6 MV)

Magnetron

  • Type: RF Oscillator (self-generating)
  • Electron motion: Circular/spiral paths (crossed E & B fields)
  • E-field: Radial (cathode → anode)
  • B-field: Axial (perpendicular to E-field)
  • Cavity resonance: Electron "spokes" induce oscillations in cavities
  • Frequency: Determined by cavity dimensions (~3 GHz)
  • Clinical use: Low-energy linacs (4-6 MV), compact & economical