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.
Gain, saturation, and bandwidth measurements of the NRL gyrotron travelling wave amplifier
Gyrotron travelling wave amplifier (gyro-TWA) experiments have been recently performed, demonstrating linear gains as high as 32 dB at 35.1 GHz for a 70 kv, 9 amp beam, and 24 dB for a 3 amp beam. The gyro-TWA operates in the TE01circular waveguide mode and at the fundamental electron cyclotron frequency. At present, it is a single stage device with no severs or stabilizing elements. The amplifier has been driven into saturation with a maximum observed output of 26 kW at 13 dB gain. Saturation begins at approximately 10 kW output with 30 dB gain. The best efficiency observed was 7.8 percent for a 3 amp beam and 20 dB gain. Linear bandwidth measurements show a -3 dB bandwidth of approximately 500 MHz for the peak gain of 24 dB with a 3 amp beam.