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

Hornstein, M.K.; Bajaj, Vikram S.; Griffin, Robert G.; Temkin, Richard J.

doi:10.1109/tps.2006.875769

Cited by 135 publications

(50 citation statements)

References 13 publications

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“…Near wavelengths corresponding to the pixel spacing (~0.1 mm), a rectilinear diffraction pattern becomes visible. Comparative measurements of another gyrotron oscillator operating in several modes from 150-460 GHz confirm that this is an artifact of the pixel spacing [47], and fitting of the images with and without image processing to eliminate these artifacts gives identical results for the case of a nearly Gaussian beam. These results are summarized in Figure 19, where Figure 19 (A) is of the raw data, Figure 19(B) is a plot of the best-fit Gaussian, and Figure 19(C) is the fitting residual.…”

Section: Pyroelectric Camera-mentioning

confidence: 85%

“…Improvements in this approach, involving asynchronous digital sampling of slowly-varying signals and asynchronous sampling of analog signals, have been demonstrated in a 460 GHz gyrotron control system [47].…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the most economical approach to generating millimeter wave power at these frequencies would be to employ an oscillator in which the output frequency is doubled, and with this approach it should be possible to use NbTi based magnets for all 1 H NMR frequencies ≤800 MHz. Second harmonic operation has recently been demonstrated in a 460 GHz CW gyrotron oscillator for DNP, which operates in a 9 T magnet [45,47].…”

Section: Second Harmonic Operationmentioning

confidence: 99%

“…A cursory description of the 250 GHz oscillator appeared elsewhere [44] and the design and initial operation of the 460 GHz oscillator is described in detail in other publications [45][46][47][48]. However, since the appearance of the brief description of the 250 GHz gyrotron, we have implemented many important changes to the system.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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: Pyroelectric Camera-mentioning

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Section: Second Harmonic Operationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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show abstract

“…[6][7][8][9][10] The gyrotron consists of several major components including a magnetron injection gun (MIG), open-ended cavity, mode converter, and collector. [11][12][13] The mode converter is critical: it converts a higher-order mode from the interaction circuit into a Gaussian-like beam, which effectively transmits RF power through free space.…”

Section: Introductionmentioning

confidence: 99%

Cold testing of quasi-optical mode converters using a generator for non-rotating high-order gyrotron modes

Kim

Choe

et al. 2014

Review of Scientific Instruments

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Selective suppression of high order axial modes of the gyrotron backward-wave oscillator Phys. Plasmas 14, 093301 (2007) In this paper, we test the performance of a quasi-optical, internal-gyrotron mode converter. When cold testing mode converters, a rotating higher-order mode is commonly used. However, this requires a nontrivial design and precise alignment. We thus propose a new technique for testing gyrotron mode converters by using a simple, non-rotating, higher-order mode generator. We demonstrate the feasibility of this technique for a W-band gyrotron quasi-optical mode converter by examining the excitation of a TE 6,2 mode from a non-rotating mode generator. Our results demonstrate that this new cold-test scheme is an easy and efficient method for verifying the performance of quasi-optical mode converters.

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Dynamic Nuclear Polarization Enhanced NMR in the Solid-State

Akbey

Franks

Linden

et al. 2013

Hyperpolarization Methods in NMR Spectroscopy

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Nuclear magnetic resonance (NMR) spectroscopy is one of the most commonly used spectroscopic techniques to obtain information on the structure and dynamics of biological and chemical materials. A variety of samples can be studied including solutions, crystalline solids, powders and hydrated protein extracts. However, biological NMR spectroscopy is limited to concentrated samples, typically in the millimolar range, due to its intrinsic low sensitivity compared to other techniques such as fluorescence or electron paramagnetic resonance (EPR) spectroscopy.Dynamic nuclear polarization (DNP) is a method that increases the sensitivity of NMR by several orders of magnitude. It exploits a polarization transfer from unpaired electrons to neighboring nuclei which leads to an absolute increase of the signal-to-noise ratio (S/N). Consequently, biological samples with much lower concentrations can now be studied in hours or days compared to several weeks.This chapter will explain the different types of DNP enhanced NMR experiments, focusing primarily on solid-state magic angle spinning (MAS) DNP, its applications, and possible means of improvement.

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

Cited by 135 publications

References 13 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

Cold testing of quasi-optical mode converters using a generator for non-rotating high-order gyrotron modes

Dynamic Nuclear Polarization Enhanced NMR in the Solid-State

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