Experimental investigation of a 140 GHz gyrotron-backward wave oscillator
- Massachusetts Institute of Technology, Cambridge, MA (United States); and others
We report the experimental operation of a voltage tunable gyrotron backward wave oscillator (gyro-BWO) in the frequency range near 140 GHz. Voltage tunability is an important feature of the gyro-BWO for application as a fast tuning source for driving high power free electron lasers or cyclotron autoresonance maser amplifiers. The gyro-BWO operated in an overmoded cylindrical waveguide structure in the TE{sub 1,2} mode. The electron beam source was a Pierce-wiggler gun producing an 80 kV, 6.2 A beam. Frequency tuning with voltage between 134 and 147 GHz was achieved in the TE{sub 1,2} mode with constant magnetic field. However, this tuning was found to be discontinuous. Output powers of up to 2 kW and 2% efficiency were found, significantly below theoretical predictions for a cold beam. The theoretical beam velocity spread was modeled by a 3D beam transport code. The code results show that space charge forces, coupled with the wiggler-induced helical motion and the short cyclotron wavelength of the beam, produce large increases in velocity spread in the magnetic compression region. A beam with smaller velocity spread would be needed to make the gyro-BWO operate at the desired efficiency.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 100192
- Journal Information:
- International Journal of Infrared and Millimeter Waves, Vol. 16, Issue 5; Other Information: PBD: May 1995
- Country of Publication:
- United States
- Language:
- English
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