A self-consistent field theory for gyrotron oscillators: application to a low<i>Q</i>gyromonotron

Fliflet, A. W.; Read, Michael; Chu, K. R.; Seeley, R.

doi:10.1080/00207218208901545

Cited by 214 publications

(40 citation statements)

References 12 publications

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“…Here we discuss relatively small variations of the output frequency, which we term frequency pulling, that describe the variation of frequency as a function of beam voltage, cathode parameters, and magnetic field while the gyroton is operating in the TE 0,3,2 mode. These effects were observed and discussed previously [109][110][111] in other gyrotrons. As illustrated in Figures 15A and 16A, B, and C the gyrotron operating frequency (and the microwave power output) is sensitive to variations in the main or auxiliary magnetic fields, the beam voltage, or beam current, and the cavity temperature (data not shown).…”

Section: Frequency Tuningsupporting

confidence: 82%

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Bajaj

Hornstein

Kreischer

et al. 2007

Journal of Magnetic Resonance

162

130

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In this paper, we describe a 250 GHz gyrotron oscillator, a critical component of an integrated system for magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments at 9T, corresponding to 380 MHz 1 H frequency. The 250 GHz gyrotron is the first gyro-device designed with the goal of seamless integration with an NMR spectrometer for routine DNP-enhanced NMR spectroscopy and has operated under computer control for periods of up to 21 days with a 100% duty cycle. Following a brief historical review of the field, we present studies of the membrane protein bacteriorhodopsin (bR) using DNP-enhanced multidimensional NMR. These results include assignment of active site resonances in [U-13 C, 15 N]-bR and demonstrate the utility of DNP for studies of membrane proteins. Next, we review the theory of gyro-devices from quantum mechanical and classical viewpoints and discuss the unique considerations that apply to gyrotron oscillators designed for DNP experiments. We then characterize the operation of the 250 GHz gyrotron in detail, including its long-term stability and controllability. We have measured the spectral purity of the gyrotron emission using both homodyne and heterodyne techniques. Radiation intensity patterns from the corrugated waveguide that delivers power to the NMR probe were measured using two new techniques to confirm pure mode content: a thermometric approach based on the temperaturedependent color of liquid crystalline media applied to a substrate and imaging with a pyroelectric camera. We next present a detailed study of the mode excitation characteristics of the gyrotron. Exploration of the operating characteristics of several fundamental modes reveals broadband continuous frequency tuning of up to 1.8 GHz as a function of the magnetic field alone, a feature that may be exploited in future tunable gyrotron designs. Oscillation of the 250 GHz gyrotron at the second harmonic of cyclotron resonance begins at extremely low beam currents (as low 12 mA) at frequencies between 320-365 GHz, suggesting an efficient route for the generation of even higher frequency radiation. The low starting currents were attributed to an elevated cavity Q, which is confirmed by cavity thermal load measurements. We conclude with an appendix containing a detailed description of the control system that safely automates all aspects of the gyrotron operation.

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Section: Frequency Tuningsupporting

confidence: 82%

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Bajaj

Hornstein

Kreischer

et al. 2007

Journal of Magnetic Resonance

162

130

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“…The slow-time-scale nonlinear equations of motion for an electron in a thin annular beam immersed in a tapered magnetic field and interacting at a particular harmonic with several circularly-polarized TE modes have been given previously by Fliflet (1986) and Fliflet et al (1982), and are given by:…”

Section: IImentioning

confidence: 99%

Multimode Simulation of High Frequency Gyrotrons.

Gold

Fliflet

1991

Self Cite

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“…Figure 6 shows the gyrotron efficiency given by theory and experiment. The theoretical curve was obtained using a nonlinear, self-consistent computer code 10 using at each beam current value, the velocity ratio value (a = 1.93) from the gun design, and the beam voltage (80 kV) typical for our gyrotron operation. Velocity spread was not included in the calculation.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Velocity ratio measurements of a gyrotron electron beam

Guss¹,

Grimm²,

Kreischer³

et al. 1991

Journal of Applied Physics

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A 140 GHz high power gyrotron has recently been operated in a 14 T Bitter magnet to characterize emission as a function of magnetic field and beam current. The velocity ratio (or pitch angle) a = (v±.)/(v 1 ) of the beam electrons is a critical parameter for high efficiency gyrotron operation and was measured using a capacitive probe located in the beam tunnel before the cavity. The observed velocity ratio decreased as the beam current increased while the beam voltage and magnetic fields were held fixed. This decrease in a partially explains the reduced gyrotron efficiency observed at high beam currents. The velocity ratio exhibited saturation effects as a function of both the beam current and the control-anode voltage, at low cathode magnetic field values. Particle code results show a decrease in a as a function of beam current that is consistent in magnitude with the observed values. 1

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A self-consistent field theory for gyrotron oscillators: application to a lowQgyromonotron

Cited by 214 publications

References 12 publications

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Multimode Simulation of High Frequency Gyrotrons.

Velocity ratio measurements of a gyrotron electron beam

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