Category Archives: THz

Opportunities and Challenges for EIK’s in DNP NMR Applications #DNPNMR

Rosay, Melanie, Ivan Scrgeyev, Leo Tometich, Christopher Hickey, Albert Roitman, Doug Yake, and Dave Berry. “Opportunities and Challenges for EIK’s in DNP NMR Applications.” 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.2018.8510328

Modern Dynamic Nuclear Polarization (DNP) experiments often utilize gyrotron sources for irradiation of electron spins at 140-593 GHz. The total cost of ownership, size, and complexity of gyrotrons, however, limits wider adoption. The introduction of lower-cost and more compact sources can have a significant impact on the DNP community. This contribution describes the development of a 263 GHz EIK, design of transmission line for optimal irradiation of the DNP NMR sample, and detailed performance characterization for DNP experiments.

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.

Laser-driven semiconductor switch for generating nanosecond pulses from a megawatt gyrotron

Picard, Julian F., Samuel C. Schaub, Guy Rosenzweig, Jacob C. Stephens, Michael A. Shapiro, and Richard J. Temkin. “Laser-Driven Semiconductor Switch for Generating Nanosecond Pulses from a Megawatt Gyrotron.” Applied Physics Letters 114, no. 16 (April 22, 2019): 164102. 

https://doi.org/10.1063/1.5093639

A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 ls, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Under the same conditions, a single GaAs wafer yielded 24 ns 110 GHz RF pulses with >78% reflectance. For both semiconductor materials, a higher value of reflectance was observed with increasing 110 GHz beam intensity. Using two active wafers, pulses of variable length down to 3 ns duration were created. The switch was tested at incident 110 GHz RF power levels up to 600 kW. A 1-D model is presented that agrees well with the experimentally observed temporal pulse shapes obtained with a single Si wafer. The LDSS has many potential uses in high power millimeter-wave research, including testing of high-gradient accelerator structures.

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.

Stabilization of Gyrotron Frequency by PID Feedback Control on the Acceleration Voltage

Khutoryan, E.M., et al., Stabilization of Gyrotron Frequency by PID Feedback Control on the Acceleration Voltage. J Infrared Milli Terahz Waves, 2015. 36(12): p. 1157-1163.

http://dx.doi.org/10.1007/s10762-015-0212-2

The results of frequency stabilization by proportional-integral-derivative (PID) feedback control of acceleration voltage in the 460-GHz Gyrotron FU CW GVI (the official name in Osaka University is Gyrotron FU CW GOI) are presented. The experiment was organized on the basis of the frequency modulation by modulation of acceleration voltage of beam electrons. The frequency stabilization during 10 h experiment was better than 10−6, which is compared with the results of the frequency deviation in free-running gyrotron operation.

Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics of various media

Glyavin, M.Y., et al., Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics of various media. Review of Scientific Instruments, 2015. 86(5): p. 054705.

doi:http://dx.doi.org/10.1063/1.4921322

A 263 GHz continuous-wave (CW) gyrotron was developed at the IAP RAS for future applications as a microwave power source in Dynamic Nuclear Polarization / Nuclear magnetic resonance(DNP/NMR) spectrometers. A new experimental facility with a computerized control was built to test this and subsequent gyrotrons. We obtained the maximum CW power up to 1 kW in the 15 kV/0.4 A operation regime. The power about 10 W, which is sufficient for many spectroscopicapplications, was realized in the low current 14 kV/0.02 A regime. The possibility of frequencytuning by variation of the coolant temperature about 4 MHz/1 °C was demonstrated. The spectral width of the gyrotron radiation was about 10−6.

High-Speed Frequency Modulation of a 460-GHz Gyrotron for Enhancement of 700-MHz DNP-NMR Spectroscopy

Idehara, T., et al., High-Speed Frequency Modulation of a 460-GHz Gyrotron for Enhancement of 700-MHz DNP-NMR Spectroscopy. J Infrared Milli Terahz Waves, 2015: p. 1-11.

http://dx.doi.org/10.1007/s10762-015-0176-2

The high-speed frequency modulation of a 460-GHz Gyrotron FU CW GVI (the official name in Osaka University is Gyrotron FU CW GOI) was achieved by modulation of acceleration voltage of beam electrons. The modulation speed fm can be increased up to 10 kHz without decreasing the modulation amplitude δf of frequency. The amplitude δf was increased almost linearly with the modulation amplitude of acceleration voltage ΔVa. At the ΔVa=1 kV, frequency spectrum width df was 50 MHz in the case of fm<10 kHz. The frequency modulation was observed as both the variation of the IF frequency in the heterodyne detection system measured by a high-speed oscilloscope and the widths of frequency spectra df measured on a frequency spectrum analyzer. Both results well agree reasonably. When fm exceeds 10 kHz, the amplitude δf is decreased gradually with increasing fm because of the degradation of the used amplifier in response for high-speed modulation. The experiment was performed successfully for both a sinusoidal wave and triangle wave modulations. We can use the high-speed frequency modulation for increasing the enhancement factor of the dynamic nuclear polarization (DNP)-enhanced nuclear magnetic resonance (NMR) spectroscopy, which is one of effective and attractive methods for the high-frequency DNP-NMR spectroscopy, for example, at 700 MHz. Because the sensitivity of NMR is inversely proportional to the frequency, high-speed frequency modulation can compensate the decreasing the enhancement factor in the high-frequency DNP-NMR spectroscopy and keep the factor at high value. In addition, the high-speed frequency modulation is useful for frequency stabilization by a PID control of an acceleration voltage by feeding back of the fluctuation of frequency. The frequency stabilization in long time is also useful for application of a DNP-NMR spectroscopy to the analysis of complicated protein molecules.

Development of the Multifrequency Gyrotron FU CW GV with Gaussian Beam Output

Tatematsu, Y., et al., Development of the Multifrequency Gyrotron FU CW GV with Gaussian Beam Output. J Infrared Milli Terahz Waves, 2015: p. 1-12.

http://dx.doi.org/10.1007/s10762-015-0173-5

Gyrotron FU CW GV has been developed as a multifrequency gyrotron for operation over the frequency range from 162 to 265 GHz at frequencies separated by steps of approximately 10 GHz. The oscillation modes were selected; the radii of the caustic surfaces for the electromagnetic waves of the modes had similar values in the waveguide, and it was therefore expected that these modes would be converted into Gaussian beams by a mode converter. In reality, more than ten modes oscillated and the Gaussian-like beams were radiated. A double-disk window with variable spacing maintains the transmittance through the window at a high level over a wide range of frequencies. Using this window, output powers of more than 1 kW were observed for almost all the expected modes.

The Development of 460 GHz gyrotrons for 700 MHz DNP-NMR spectroscopy

Idehara, T., et al., The Development of 460 GHz gyrotrons for 700 MHz DNP-NMR spectroscopy. J Infrared Milli Terahz Waves, 2015: p. 1-15.

http://dx.doi.org/10.1007/s10762-015-0150-z

Two demountable gyrotrons with internal mode converters were developded as sub-THz radiation sources for 700 MHz DNP (Dynamic Nuclear Polarization) enhanced NMR spectroscopy. Experimental study on the DNP-NMR spectroscopy will be carried out in Osaka University, Institute for Protein Research, as a collaboration with FIR UF. Both gyrotrons operate near 460 GHz and the output CW power measured at the end of transmission system made by circular waveguides is typically 20 to 30 watts. One of them named Gyrotron FU CW GVI (we are using “Gyrotron FU CW GO-1” as an official name in Osaka University) is designed to have a special function of high speed frequency modulation δf within 100 MHz band. This will expand excitable band width of ESR and increase the number of electron spins contributing to DNP. The other gyrotron, Gyrotron FU CW GVIA (“Gyrotron FU CW GO-II”) has a function of frequency tunability Δf in the range of wider than 1.5 GHz, which is achieved in steady state by changing magnetic field intensity. This function should be used for adjusting the output frequency at the optimal value to achieve the highest enhancement factor of DNP.

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.