Category Archives: Gyrotron

Second Harmonic 527-GHz Gyrotron for DNP-NMR: Design and Experimental Results #DNPNMR

Jawla, Sudheer K., Robert G. Griffin, Ivan A. Mastovsky, Michael A. Shapiro, and Richard J. Temkin. “Second Harmonic 527-GHz Gyrotron for DNP-NMR: Design and Experimental Results.” IEEE Transactions on Electron Devices 67, no. 1 (January 2020): 328–34.

https://doi.org/10.1109/TED.2019.2953658

We report the design and experimental demonstration of a frequency tunable terahertz gyrotron at 527 GHz built for an 800-MHz dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP-NMR) spectrometer. The gyrotron is designed at the second harmonic (ω = 2ωc) of the electron cyclotron frequency. It produces up to 9.3-W continuous microwave (CW) power at 527.2-GHz frequency using a diode type electron gun operating at V = 16.65 kV, Ib = 110 mA in a TE11,2,1 mode, corresponding to an efficiency of ∼0.5%. The gyrotron is tunable within ∼0.4 GHz by combining voltage and magnetic field tuning. The gyrotron has an internal mode converter that produces a Gaussian-like beam that couples to the HE11 mode of an internal 12-mm i.d. corrugated waveguide periscope assembly leading up to the output window. An external corrugated waveguide transmission line system is built including a corrugated taper from 12- to 16-mm i.d. waveguide followed by 3 m of the 16-mm i.d. waveguide The microwave beam profile is measured using a pyroelectric camera showing ∼84% HE11 mode content.

State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers

Everything you ever wanted to know about gyrotrons, their applications and their design is summarized in this article. With a whooping 1528 references this article will be the encyclopedia of gyrotrons for many years to come.

Thumm, Manfred. “State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers.” Journal of Infrared, Millimeter, and Terahertz Waves, January 3, 2020.

https://doi.org/10.1007/s10762-019-00631-y

This paper presents a review of the experimental achievements related to the development of high-power gyrotron oscillators for long-pulse or CWoperation and pulsed gyrotrons for many applications. In addition, this work gives a short overview on the present development status of frequency step-tunable and multi-frequency gyrotrons, coaxialcavity multi-megawatt gyrotrons, gyrotrons for technological and spectroscopy applications, relativistic gyrotrons, large orbit gyrotrons (LOGs), quasi-optical gyrotrons, fastand slow-wave cyclotron autoresonance masers (CARMs), gyroklystrons, gyro-TWT amplifiers, gyrotwystron amplifiers, gyro-BWOs, gyro-harmonic converters, gyropeniotrons, magnicons, free electron masers (FEMs), and dielectric vacuum windows for such high-power mm-wave sources. Gyrotron oscillators (gyromonotrons) are mainly used as high-power millimeter wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control, and diagnostics of magnetically confined plasmas for clean generation of energy by controlled thermonuclear fusion. The maximum pulse length of commercially available 140 GHz, megawattclass gyrotrons employing synthetic diamond output windows is 30 min (CPI and European KIT-SPC-THALES collaboration). The world record parameters of the European tube are as follows: 0.92 MW output power at 30-min pulse duration, 97.5% Gaussian mode purity, and 44% efficiency, employing a single-stage depressed collector (SDC) for energy recovery. A maximum output power of 1.5 MWin 4.0-s pulses at 45% efficiency was generated with the QST-TOSHIBA (now CANON) 110-GHz gyrotron. The Japan 170-GHz ITER gyrotron achieved 1 MW, 800 s at 55% efficiency and holds the energy world record of 2.88 GJ (0.8 MW, 60 min) and the efficiency record of 57% for tubes with an output power of more than 0.5 MW. The Russian 170-GHz ITER gyrotron obtained 0.99 (1.2) MW with a pulse duration of 1000 (100) s and 53% efficiency. The prototype tube of the European 2-MW, 170-GHz coaxial-cavity gyrotron achieved in short pulses the record power of 2.2 MW at 48% efficiency and 96% Gaussian mode purity. Gyrotrons with pulsed magnet for various short-pulse applications deliver Pout = 210 kW with τ = 20 μs at frequencies up to 670 GHz (η ≅ 20%), Pout = 5.3 kW at 1 THz (η = 6.1%), and Pout = 0.5 kW at 1.3 THz (η = 0.6%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require tubes with the following parameters: f > 24 GHz, Pout = 4–50 kW, CW, η > 30%. The CW powers produced by gyroklystrons and FEMs are 10 kW (94 GHz) and 36W(15 GHz), respectively. The IR FEL at the Thomas Jefferson National Accelerator Facility in the USA obtained a record average power of 14.2 kW at a wavelength of 1.6 μm. The THz FEL (NOVEL) at the Budker Institute of Nuclear Physics in Russia achieved a maximum average power of 0.5 kW at wavelengths 50– 240 μm (6.00–1.25 THz).

High power Continuously Frequency-tunable Terahertz Radiation Sources and Transmission Lines for DNP-enhanced NMR System #DNPNMR

Liu, Diwei, Tao Song, Hao Shen, Jie Huang, Ning Zhang, Chenghai Wang, Wei Wang, and Shenggang Liu. “High Power Continuously Frequency-Tunable Terahertz Radiation Sources and Transmission Lines for DNP-Enhanced NMR System.” In 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 1–2. Nagoya: IEEE, 2018. 

https://doi.org/10.1109/IRMMW-THz.2018.8510299

The effect of the electron beam quality of a 250GHz continuously frequency-tunable gyrotron used for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance is tuned by changing the operating voltage V0 or the operating magnetic field B0 on the operating frequency and the beam-wave interaction efficiency is investigated. Meanwhile, an improved transmission and mirror system with a well-focused Gaussian-like output beam is designed to match the DNP-NMR sample.

Frequency-chirped dynamic nuclear polarization with magic angle spinning using a frequency-agile gyrotron #DNPNMR

Gao, Chukun, Nicholas Alaniva, Edward P. Saliba, Erika L. Sesti, Patrick T. Judge, Faith J. Scott, Thomas Halbritter, Snorri Th. Sigurdsson, and Alexander B. Barnes. “Frequency-Chirped Dynamic Nuclear Polarization with Magic Angle Spinning Using a Frequency-Agile Gyrotron.” Journal of Magnetic Resonance 308 (November 2019): 106586.

https://doi.org/10.1016/j.jmr.2019.106586

We demonstrate that frequency-chirped dynamic nuclear polarization (DNP) with magic angle spinning (MAS) improves the enhancement of nuclear magnetic resonance (NMR) signal beyond that of continuous-wave (CW) DNP. Using a custom, frequency-agile gyrotron we implemented frequencychirped DNP using the TEMTriPol-1 biradical, with MAS NMR at 7 Tesla. Frequency-chirped microwaves yielded a DNP enhancement of 137, an increase of 19% compared to 115 recorded with CW. The chirps were 120 MHz-wide and centered over the trityl resonance, with 7 W microwave power incident on the sample (estimated 0.4 MHz electron spin Rabi frequency). We describe in detail the design and fabrication of the frequency-agile gyrotron used for frequency-chirped MAS DNP. Improvements to the interaction cavity and internal mode converter yielded efficient microwave generation and mode conversion, achieving >10 W output power over a 335 MHz bandwidth with >110 W peak power. Frequency-chirped DNP with MAS is expected to have a significant impact on the future of magnetic resonance.

Frequency-chirped dynamic nuclear polarization with magic angle spinning using a frequency-agile gyrotron #DNPNMR

Gao, Chukun, Nicholas Alaniva, Edward P. Saliba, Erika L. Sesti, Patrick T. Judge, Faith J. Scott, Thomas Halbritter, Snorri Th. Sigurdsson, and Alexander B. Barnes. “Frequency-Chirped Dynamic Nuclear Polarization with Magic Angle Spinning Using a Frequency-Agile Gyrotron.” Journal of Magnetic Resonance 308 (November 2019): 106586.

https://doi.org/10.1016/j.jmr.2019.106586.

We demonstrate that frequency-chirped dynamic nuclear polarization (DNP) with magic angle spinning (MAS) improves the enhancement of nuclear magnetic resonance (NMR) signal beyond that of continuous-wave (CW) DNP. Using a custom, frequency-agile gyrotron we implemented frequencychirped DNP using the TEMTriPol-1 biradical, with MAS NMR at 7 Tesla. Frequency-chirped microwaves yielded a DNP enhancement of 137, an increase of 19% compared to 115 recorded with CW. The chirps were 120 MHz-wide and centered over the trityl resonance, with 7 W microwave power incident on the sample (estimated 0.4 MHz electron spin Rabi frequency). We describe in detail the design and fabrication of the frequency-agile gyrotron used for frequency-chirped MAS DNP. Improvements to the interaction cavity and internal mode converter yielded efficient microwave generation and mode conversion, achieving >10 W output power over a 335 MHz bandwidth with >110 W peak power. Frequency-chirped DNP with MAS is expected to have a significant impact on the future of magnetic resonance.

Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization #DNPNMR

Scott, F.J., et al., Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization. J Magn Reson, 2018. 289: p. 45-54.

https://www.ncbi.nlm.nih.gov/pubmed/29471275

We describe a frequency-agile gyrotron which can generate frequency-chirped microwave pulses. An arbitrary waveform generator (AWG) within the NMR spectrometer controls the microwave frequency, enabling synchronized pulsed control of both electron and nuclear spins. We demonstrate that the acceleration of emitted electrons, and thus the microwave frequency, can be quickly changed by varying the anode voltage. This strategy results in much faster frequency response than can be achieved by changing the potential of the electron emitter, and does not require a custom triode electron gun. The gyrotron frequency can be swept with a rate of 20MHz/mus over a 670MHz bandwidth in a static magnetic field. We have already implemented time-domain electron decoupling with dynamic nuclear polarization (DNP) magic angle spinning (MAS) with this device. In this contribution, we show frequency-swept DNP enhancement profiles recorded without changing the NMR magnet or probe. The profile of endofullerenes exhibits a DNP profile with a <10MHz linewidth, indicating that the device also has sufficient frequency stability, and therefore phase stability, to implement pulsed DNP mechanisms such as the frequency-swept solid effect. We describe schematics of the mechanical and vacuum construction of the device which includes a novel flanged sapphire window assembly. Finally, we discuss how commercially available continuous-wave gyrotrons can potentially be converted into similar frequency-agile high-power microwave sources.

High-power sub-terahertz source with a record frequency stability at up to 1 Hz #DNPNMR

Fokin, A., et al., High-power sub-terahertz source with a record frequency stability at up to 1 Hz. Sci Rep, 2018. 8(1): p. 4317.

https://www.ncbi.nlm.nih.gov/pubmed/29531359

Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10(-4). Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0.263 THz/100 W gyrotron are 4 x 10(-12) and 10(-10), respectively, and these parameters are better than those demonstrated so far with high-power sources by almost three orders of magnitude. This approach confirms its potential for ultra-high precision spectroscopy, the development of sources with large-scale radiating apertures, and other new projects.

A novel THz-band double-beam gyrotron for high-field DNP-NMR spectroscopy

Idehara, T., et al., A novel THz-band double-beam gyrotron for high-field DNP-NMR spectroscopy. Review of Scientific Instruments, 2017. 88(9): p. 094708.

http://dx.doi.org/10.1063/1.4997994

We present the first experimental results of the study on a novel second harmonic THz-band doublebeam gyrotron. The tube has demonstrated a stable single-mode operation with output parameters that are appropriate for the next-generation 1.2 GHz dynamic nuclear polarization-nuclear magnetic resonance spectroscopy. Besides the design mode (TE8,5), a series of other fundamental and second harmonic modes have been excited. This makes the new gyrotron a versatile radiation source, which can be used also in other applications of the high-power science and technologies.

A ferromagnetic shim insert for NMR magnets – Towards an integrated gyrotron for DNP-NMR spectroscopy #DNPNMR

Bridge12 is currently developing an integrated THz system for NMR-DNP spectroscopy. The basic idea is to operate the gyrotron inside the NMR magnet, just above the NMR probe head, effectively eliminating the need of a second superconducting magnet. This article is about a ferroshim insert that we had to develop for this purpose.

Ryan, H., J. van Bentum, and T. Maly, A ferromagnetic shim insert for NMR magnets – Towards an integrated gyrotron for DNP-NMR spectroscopy. J. Magn. Reson., 2017. 277: p. 1-7.

http://www.sciencedirect.com/science/article/pii/S1090780717300290

In recent years high-field Dynamic Nuclear Polarization (DNP) enhanced NMR spectroscopy has gained significant interest. In high-field DNP-NMR experiments (⩾400 MHz 1H NMR, ⩾9.4 T) often a stand-alone gyrotron is used to generate high microwave/THz power to produce sufficiently high microwave induced B1e fields at the position of the NMR sample. These devices typically require a second, stand-alone superconducting magnet to operate. Here we present the design and realization of a ferroshim insert, to create two iso-centers inside a commercially available wide-bore NMR magnet. This work is part of a larger project to integrate a gyrotron into NMR magnets, effectively eliminating the need for a second, stand-alone superconducting magnet.

Gyrotrons for High-Power Terahertz Science and Technology at FIR UF #DNPNMR

Idehara, T. and S.P. Sabchevski, Gyrotrons for High-Power Terahertz Science and Technology at FIR UF. J Infrared Milli Terahz Waves, 2016: p. 1-25.

http://dx.doi.org/10.1007/s10762-016-0314-5

In this review paper, we present the recent progress in the development of a series of gyrotrons at the Research Center for Development of Far-Infrared Region, University of Fukui, that have opened the road to many novel applications in the high-power terahertz science and technology. The current status of the research in this actively developing field is illustrated by the most representative examples in which the developed gyrotrons are used as powerful and frequency-tunable sources of coherent radiation operating in a continuous-wave regime. Among them are high-precision spectroscopic techniques (most notably dynamic nuclear polarization-nuclear magnetic resonance, electron spin resonance, X-ray detected magnetic resonance, and studies of the hyperfine splitting of the energy levels of positronium), treatment and characterization of advanced materials, and new medical technologies.

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