R.J. Temkin

Experimental results from the MIT 140 GHz quasioptical gyro-TWT

We present the latest experimental results from a novel 140 GHz quasioptical gyro-TWT at MIT. The gyro-TWT is designed to operate in a higher order HE/sub 06/ mode of a confocal waveguide to produce 100 kW at 140 GHz with a gain of 38 dB. Current experimental results have demonstrated a peak power of 30 kW at 140 GHz with a gain of 29 dB and an unsaturated 3 dB bandwidth of 2.0 GHz. The gyro-TWT interaction structure which is formed by a pair of confocal mirrors exhibits tremendous potential for high average power operation in the W-band and beyond.

Design of a 460 GHz second harmonic gyrotron oscillator for use in dynamic nuclear polarization

We report the design of a gyrotron oscillator for continuous operation at 460 GHz at a power level of up to 50 W. The gyrotron oscillator will be used in dynamic nuclear polarization (DNP) NMR (nuclear magnetic resonance) studies with a 700 MHz (/sup 1/H), 16.5 T NMR spectrometer and will operate at the second harmonic of the electron cyclotron frequency.

Initial experimental results from the MIT 140 GHz quasioptical gyro-TWT

We present the latest experimental results from a novel 140 GHz quasioptical gyro-TWT at MIT. The gyro-TWT is designed to operate in a higher order HE/sub 06/ mode of a confocal waveguide to produce 100 kW at 140 GHz with a gain of 38 dB. Current experimental results have demonstrated a peak power of 30 kW at 140 GHz with a gain of 29 dB and an unsaturated 3 dB bandwidth of 2.0 GHz. The gyro-TWT interaction structure which is formed by a pair of confocal mirrors exhibits tremendous potential for high average power operation in the W-band and beyond.

A 250 GHz gyrotron for NMR spectroscopy

Summary form only given. A gyrotron-based spectrometer suitable for nuclear magnetic resonance (NMR) studies at 380 MHz has been constructed. This spectrometer is being used to study dynamic nuclear polarization (DNP), a technique that can result in significant enhancement of the NMR signal. Signal enhancements up to forty have been measured in the /sup 13/C spectra of glycerol/water/TEMPO. An important component of this system is a compact 250 GHz fundamental gyrotron oscillator operating in the TE/sub 031/ mode. This source typically operates at a beam voltage of 12-16 kV, and at currents up to 50 mA. A 9.4 T magnet with a 6.4 cm diameter vertical bore produces the magnetic field. The gyrotron occupies the vertical bore, while a radial bore is used for the transmission of the microwave power through a side vacuum window of the tube. As a result, the electron beam and microwave power can be separated just after the interaction in the gyrotron cavity. This reduces ohmic losses in the output waveguide, and simplifies the design of the beam collector. An internal quasi-optical mode converter is used to convert the TE/sub 031/ cavity mode into a Gaussian output beam.

Mode conversion losses in ITER transmission lines

Mode conversion in miter bends and polarizers is the main contributor of loss in the transmission lines (TLs) for the ITER 170 GHz ECH system, which should transport one megawatt of power with the smallest possible loss. Previous loss estimates assumed that the power in the TL was carried by a pure HE11 mode; however, in practice, there is significant power in higher order modes (HOMs). It is shown that the mode conversion loss of the power in an HE11 mode at a miter bend is greatly altered by the presence of even a small proportion of HOMs in the TL, and is a strong function of both the magnitude of the HOM and its phase relative to that of the HE11 mode. The resulting total loss in the ITER transmission lines is expected to be very different from the loss previously predicted using single mode theory.

Recent results for the 1.5-MW, 110-GHz gyrotron experiment

High power gyrotrons used for ECH heating of the DIII-D Tokamak at General Atomics have been able to produce 1 MW at 110 GHz for close to 10 s. The next generation of these tubes is being designed and built to produce 1.5 MW. The gyrotron design includes a 96 W, 40 A MIG electron gun to achieve a microwave efficiency of 39% in the TE/sub 22,6/ mode. The physics and engineering features of the 1.5 MW, 110 GHz gyrotron are being examined at MIT, where a short (3 /spl mu/s) pulse experimental version of the gyrotron is used for testing the gun and cavity design. In this study we present the most recent results of these experiments.

Harmonic results of a 460 GHz gyrotron

We report the first results of a 460 GHz second harmonic gyrotron. In microsecond pulse length operation at 13 kV and 110 mA, power levels in the order of 1 W have been observed at the TE/sub 2,6/ mode at 456.2 GHz and the TE/sub 0,6/ mode at 458.6 GHz. Modes at the fundamental, including the TE/sub 0,3/ at 238 GHz and the TE/sub 2,3/ at 233 GHz, have output powers up to 70 W. The TE/sub 5,2/ mode was observed to tune continuously in frequency from 246 GHz to 248 GHz. The gyrotron is being processed for CW operation. At present, more than 12 W have been obtained in CW operation in the TE/sub 2,3/ mode at 233 GHz.

CW results of a 460 GHz second harmonic gyrotron oscillator - for sensitivity enhanced NMR

We report microsecond pulse and CW results of a gyrotron operating near 460 GHz and 230 GHz at the second electron cyclotron harmonic and fundamental, respectively. Peak power levels of up to 70 W at the fundamental and 3 W at the second harmonic have been obtained in operation at up to 13 kV and 150 mA. The gyrotron has been operated continuously to achieve 3 W CW at the second harmonic. The gyrotron was also demonstrated as a wideband continuous frequency tunable oscillator by magnetically exciting fundamental higher order longitudinal modes. The gyrotron oscillator can be used for dynamic nuclear polarization (DNP) studies in conjunction with a 700 MHz (/sup 1/H), 16.5 T nuclear magnetic resonance (NMR) spectrometer.

CW second harmonic results at 460 GHz of a gyrotron oscillator - for sensitivity enhanced NMR

We report 460 and 233 GHz CW results of a gyrotron operating at the second electron cyclotron harmonic and fundamental, respectively. A record CW power level of over 8 W has been obtained at 460 GHz in the TE/sub 0,6/ mode with 12.4 kV and 135 mA. The gyrotron has operated under computer control for over an hour with stable power output of better than 1%. Fundamental CW studies at 233 GHz in the TE/sub 2,3/ mode reveal that oscillations start with less than 7 W of beam power below 3.5 kV. The gyrotron will extend sensitivity-enhanced NMR through dynamic nuclear polarization to the highest field ever used, 16.5 T (700 MHz /sup 1/H).

Design of a 140 GHz, 100 W gyroklystron amplifier

Summary form only given. We present the preliminary design and the simulation results for a 140 GHz, 100 W CW gyroklystron amplifier for use in dynamic nuclear polarization (DNP) experiments. The amplifier operates with a 10 kV, 100 mA electron beam and simulations show a saturated gain of 32 dB at /spl alpha/=1.4 for the TE/sub 02/ mode with an efficiency of 9% and output power of 86 W. The use of photonic band gap (PBG) cavities to suppress mode competition is also under evaluation.