Continuous-wave operation of a 460-GHz second harmonic gyrotron oscillator

We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE0,6,1 mode near 460 GHz. The gyrotron also operates in the second harmonic TE2,6,1 mode at 456 GHz and in the TE2,3,1 fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE 0,6,1 mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T

[1]  R. Griffin,et al.  Second harmonic operation at 460 GHz and broadband continuous frequency tuning of a gyrotron oscillator , 2005, IEEE Transactions on Electron Devices.

[2]  O. Dumbrajs,et al.  Technical noise in gyroklystrons and phase-locked gyrotron oscillators , 1997 .

[3]  Gregory S. Nusinovich,et al.  Submillimeter-wave gyrotrons: Theory and experiment , 1983 .

[4]  T. Idehara,et al.  CW Operation of a Submillimeter Wave Gyrotron (Gyrotron Fu IV) for High Stability of the Output Frequency , 1998 .

[5]  B. G. Danly,et al.  Frequency pulling and bandwidth measurements of a 140 GHz pulsed gyrotron , 1984 .

[6]  Kan-Nian Hu,et al.  Operational characteristics of a 14-W 140-GHz gyrotron for dynamic nuclear polarization , 2006, IEEE Transactions on Plasma Science.

[7]  Baruch Levush,et al.  MAGY: a time-dependent code for simulation of slow and fast microwave sources , 1998 .

[8]  Gregory S. Nusinovich,et al.  Effect of technical noise on radiation linewidth in free-running gyrotron oscillators , 1997 .

[9]  R G Griffin,et al.  Dynamic nuclear polarization at 9T using a novel 250GHz gyrotron microwave source. , 2003, Journal of magnetic resonance.

[10]  Paul P. Woskov,et al.  250 GHz CW Gyrotron Oscillator for Dynamic Nuclear Polarization in Biological Solid State NMR , 2008 .

[11]  Toshitaka Idehara,et al.  A 150–600 GHz step‐tunable gyrotron , 1993 .

[12]  R. Griffin,et al.  A 250 GHz gyrotron for NMR spectroscopy , 2000, ICOPS 2000. IEEE Conference Record - Abstracts. 27th IEEE International Conference on Plasma Science (Cat. No.00CH37087).