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

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## Abstract

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 *f* _{ m } can be increased up to 10 kHz without decreasing the modulation amplitude δ*f* of frequency. The amplitude δ*f* was increased almost linearly with the modulation amplitude of acceleration voltage Δ*V* _{a}. At the Δ*V* _{a} = 1 kV, frequency spectrum width *df* was 50 MHz in the case of *f* _{ m } < 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 *f* _{ m } exceeds 10 kHz, the amplitude δ*f* is decreased gradually with increasing *f* _{ m } 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.

## Keywords

Gyrotron Second harmonic DNP NMR Sub-THz Frequency modulation## Notes

### Acknowledgments

This work was partially supported by Grants in Aid for Scientific Research (B) (No. 24360142) and for Challenging Exploratory Research (No. 25630134) from Japan Society for Promotion of Science (JSPS) and SENTAN project of JST. This work was performed under the Cooperative Research Programs of Institute for Protein Research, Osaka University and Research Center for Development of Far Infrared Region, University of Fukui (FIR UF).

## References

- 1.M. Thumm, State-of-the-Art of High Power Gyro-Devices and Free Electron Masers, KIT Scientific Reports 7662 (2013).Google Scholar
- 2.S.E. Spira-Hakkarainen, K.E. Kreischer, R.J. Temkin, Submillimeter-wave harmonic gyrotron experiment, IEEE Trans. Plasma Science, PS-18, 334–342 (1990).CrossRefGoogle Scholar
- 3.T. Idehara, T. Tatsukawa, I. Ogawa, H. Tanabe, T. Mori, S. Wada and T. Kanemaki, Development of a second cyclotron harmonic gyrotron operating at 0.8 mm wavelength, Appl. Phys. Letts. 56, 1743–1745 (1990).CrossRefGoogle Scholar
- 4.V.A. Flyagin, A.G. Luchinin, G.S. Nusinovich, Submillimeter wave gyrotrons theory and experiment, Int. J. Infrared and Millimeter Waves 4, 629–637 (1983).CrossRefGoogle Scholar
- 5.G.F. Brand, P.W. Fekete, K. Hong, K.J. Moore and T. Idehara, Operation of a tunable gyrotron at the second harmonic of the electron cyclotron frequency, Int. J. Electronics 68, 1099–1111 (1990).CrossRefGoogle Scholar
- 6.T. Idehara, H. Tsuchiya, O. Watanabe, La Agusu and S. Mitsudo, The first experiment of a THz gyrotron with a pulse magnet, Int. J. Infrared and Millimeter Waves 27, 319–331 (2006).CrossRefGoogle Scholar
- 7.M.Y. Glyavin, A.G. Luchinin, G.Y. Golubiatnikov, Generation of 1.5-kW, 1 THz coherent radiation from a gyrotron with a pulsed magnetic field, Phys. Rev. Letts. 100, 015101-1∼015102-3 (2008).CrossRefGoogle Scholar
- 8.O. Watanabe, H. Tsuchiya, H. Mori, La Agusu, S. Mitsudo, I. Ogawa,T. Saito, T. Idehara, Development of a Tera Hertz Gyrotron as a Radiation Source, Plasma and Fusion Research: Rapid Communications 2, 024 (2007).Google Scholar
- 9.T. Idehara, T. Tatsukawa,I. Ogawa, Y. Shimizu, N. Nishida and K. Yoshida, Development and applications of submillimeter wave gyrotrons, Proc. 3rd Int. Workshop on Strong Micrawaves in Plasmas, Nizhny Novgorod, 1997, Vol.2, 634–659.Google Scholar
- 10.M. Thumm, Progress on gyrotrons for ITER and future thermonuclear fusion reactor, IEEE Trans. On Plasma Science 39, 971–979 (2011).CrossRefGoogle Scholar
- 11.Y. Bykov, A.F.L. Goldenberg, V. A. Flyagin, The possibilities of material processing by intense millimeter-wave radiation, Mat. Res. Soc. Symp. Proc., 169, 41–42 (1991).Google Scholar
- 12.T. Kikunaga, H. Asano, Y. Yasojima, F. Sato, T. Tsukamoto, A 28 GHz gyrotron with a permanent magnet system, Int. J. Electronics, 79, 655–663 (1995).CrossRefGoogle Scholar
- 13.V.S. Bajaj, C.T. Farrar, M.K. Hornstein, I. Mostovsky, J. Vieregg, J. Bryant, B. Elena, K.E. Kreischer, R.J. Temkin, R.G. Griffin, Dynamic nuclear polarization at 9 T using anovel 250 GHz gyrotron microwave source, J. Magnetic Resonance 160, 85–90 (2003).CrossRefGoogle Scholar
- 14.Yoh Matsuki, Keisuke Ueda, Toshitaka Idehara, Ryosuke Ikeda, Isamu Ogawa, Shinji Nakamura, Mitsuru Toda, Takahiro Anai, Toshimichi Fujiwara, Helium-cooling and -spinning dynamic nuclear polarization for sensitivity-enhanced solid-state NMR at 14 T and 30 K, Journal of Magnetic Resonance 225, 1–9 (2012).CrossRefGoogle Scholar
- 15.Kevin J. Pike, Thomas F. Kemp, Hiroki Takahashi, Robert Day, Andrew P. Howes, Eugeny V. Kryukov, James F. MacDonald, Alana E. C. Collis, David R. Bolton, Richard J. Wylde, Marcella Orwick, Kosuke Kosuga, Andrew J. Clark, Toshitaka Idehara, Anthony Watts, Graham M. Smith, Mark E. Newton, Ray Dupree, Mark E. Smith, A spectrometer designed for 6.7 and 14.1 T DNP-enhanced solid-state MAS NMR using quasi-optical microwave transmission, Journal of Magnetic Resonance 215, 1–9 (2012).CrossRefGoogle Scholar
- 16.S. Alberti, J. Ph. Ansermet, F. Braunmuller, P. Cuanillon, J. Dubray, D. Fasel, J. Ph. Hogge, A. Macor, E. de Rijk, M.Q. Tran, T.M. Tran, Q. Vuillemin, Experimental results on a modular gyrotron operating at 0.26 THz for 400 MHz DNP/NMR spectroscopy application, 38th Int. Conf. on Infrared. Millimeter and Terahertz Waves (IRMMW-THz 2012), Wollongong, Australia, Sept 23–28, 2012, Thu-A-3.Google Scholar
- 17.T. Yamazaki, A. Miyazaki, T. Suehara, T. Namba, S. Asai, T. Kobayashi, H. Saito, I. Ogawa, T. Idehara, S. Sabchevski. Ditect observation of the hyperfine transition of ground-state positronium, Phys. Rev. Letts. 108, 253401–5 (2012).CrossRefGoogle Scholar
- 18.I. Ogawa, M. Iwata, T Idehara, K. Kawahata, H. Iguchi, A. Ejiri, Plasma Scattering Measurement using a submillimeter wave gyrotron (Gyrotron FU II) as a power source, FusionEngineering and Design, 34–35, 455–458 (1997).CrossRefGoogle Scholar
- 19.T. Tatsukawa, T. Maeda, H. Sasai, T. Idehara, M. Mekata, T. Saito and T. Kanemaki, ESR spectrometer with a wide frequency range using a gyrotron as aradiation power source, Int. J. Infrared Millimeter Waves 16, 293–305 (1995).CrossRefGoogle Scholar
- 20.A. Rogalev, J. Goulon, G. Goujon, F. Wilhelm, I. Ogawa and T. Idehara, X-ray detected magnetic resonance at sub-THz frequencies using a high power gyrotron, J. Infrared, Millimeter and Terahertz Waves 33, 777–793 (2012).CrossRefGoogle Scholar
- 21.K.R. Thurber, W.M. Yau, R. Tycko, Low-temperature dynamic nuclear polarization at 9.4 T with a 30 mW microwave source , J. Magn. Reson. 204 (2) (2010) 303.CrossRefGoogle Scholar
- 22.T. Idehara, M. Pereyaslavets, N. Nishida, K. Yoshida and I. Ogawa, Frequency modulation in a submillimeter-wave gyrotron, Phys. Rev. Letts. 81, 1973–1976 (1998).CrossRefGoogle Scholar
- 23.O. Dumbrajs, T. Idehara, T. Saito and Y. Tatematsu, Calculations of Starting Currents and Frequencies in Frequency-Tunable Gyrotrons, Japanese Journal of Applied Physics 51, (2012) 126601.CrossRefGoogle Scholar
- 24.T. Idehara, Y. Tatematsu, Y. Yamaguchi, E.M. Khutoryan, A.N. Kuleshov, K. Ueda,Y. Matsuki and T. Fujiwara, Development of 460 GHz gyrotrons for 700 MHz DNP-NMR spectroscopy, J. Infrared, Millimeter and Terahertz Waves, under review.Google Scholar