An Experimental Second-Harmonic Axis-Encircling Beam Gyro-TWT
Despite the bright potential as a broad band source for future radar and communication applications, the area of harmonic gyro-TWTs with axis-encircling beams has been relatively unexplored. A second-harmonic TE21 gyro-TWT has been constructed at UCD that is predicted to produce 50 kW in Ka-band with 20% efficiency, 30 dB saturated gain and 3% bandwidth and is ready for hot testing. The device is driven by an axis-encircling electron beam from a novel Northrop Grumman cusp gun.
Cusp gun TE/sub 21/ second-harmonic Ka-band gyro-TWT amplifier
A second-harmonic TE/sub 21/ gyrotron traveling-wave tube (gyro-TWT) amplifier with an axis-encircling electron beam is being constructed at the University of California-Davis that is predicted to double the efficiency of our previous 200-kW 12%-efficient magnetron injection gun (MIG) TE/sub 21//sup (2)/ gyro-TWT. Both devices employ a sliced mode-selective circuit to suppress the odd-order azimuthal modes. The new device will avoid the loss in efficiency that is due to off-axis electrons interacting with the resulting linearly polarized mode. The amplifier is predicted by our large signal code to produce 50 kW in Ka-band with 20% efficiency, 30 dB saturated gain, and 3% bandwidth. The 70-kV 3.5-A axis-encircling electron beam with /spl upsi//sub /spl perp////spl upsi//sub z/ = 1.2 and /spl Delta//spl upsi//sub z///spl upsi//sub z/ = 7% will be produced by a Cusp electron gun delivered by Northrop Grumman. The amplifier has been designed using linear theory to provide a 30% safety margin from absolute instability. Distributed loss is added to the first 30.5 cm of the circuit to ensure the device is stable to harmonic gyro-BWO. The last 11.5 cm of the circuit is standard copper to avoid attenuating the wave at high power levels.
Theory and experiment of ultrahigh-gain gyrotron traveling wave amplifier
Physics and technology issues of importance to the high-gain gyrotron traveling wave amplifier (gyro-TWT) are investigated in theory and experiment. The gyro-TWT is known to be highly susceptible to spurious oscillations, especially in high gain operations. In the current study, oscillations of various origins are classified and characterized with detailed theoretical modeling. They are shown to be intricately connected to the interplay between the absolute/convective instabilities, circuit losses, and reflective feedback. Knowledge of these processes leads to the concept of an ultra high gain scheme which employs distributed wall losses for the suppression of spurious oscillations. A proof-of-principle Ka-band gyro-TWT experiment stable at zero drive has produced 93 kW saturated peak power at 26.5% efficiency and 70 dB gain, with a 3 dB saturated output power bandwidth of 3 GHz. The saturated gain is more than 30 dB beyond that previously achieved.