Stable operation of a slotted third-harmonic gyro-TWT amplifier

Summary form only given. A low magnetic field, moderate voltage gyrotron amplifier has been designed in collaboration with CPI/Varian for stable, high performance operation at 95 GHz and tested in a scaled experiment at 10 GHz. A slotted interaction circuit is utilized to achieve strong amplification at the third harmonic. The start-oscillation conditions were determined by an analytical theory that will be described. The dominant threat to the amplifier´s stability is from a third-harmonic peniotron backward-wave interaction. A self-consistent slow-timescale particle-tracing simulation code predicts the three-section, slotted third-harmonic gyro-TWT, which utilizes an 11.6 kG magnet and a 50 kV, 3 A, v/sub /spl perp///v/sub z/=1.4, axis-encircling electron beam with an axial velocity spread of 6%, will yield an output power of 30 kW with an efficiency of 20%, a saturated gain of 40 dB and a constant-drive bandwidth of 2%. This design has been tested in a scaled X-band experiment. Since the appropriate electron gun, a Cusp gun, is currently under development and not yet available, a gyroresonant rf accelerator has been used to produce the required axis-encircling electron beam.