FIR UF Research Articles

High Purity Mode CW Gyrotron Covering the Subterahertz to Terahertz Range Using a 20 T Superconducting Magnet

In this paper, we present the current status and both the ongoing investigation and the continuous improvements to the operational performance of a unique gyrotron, which is built using a 20 T superconducting magnet and holds a world record of 10-W terahertz wave generation at the highest frequency (1.08 THz) in the continuous wave (CW) operation. In addition, it has demonstrated high-purity single-mode generation on a sequence of modes that cover a wide range from subterahertz to terahertz frequencies at both the fundamental and second-harmonic resonances of the electron cyclotron frequency. As an illustration, the measurements of the observed radiation patterns of eight output modes radiated from a currently used resonant cavity with a linear up-taper are presented and compared with the corresponding patterns simulated by scattering matrix calculations. A new design of an optimized cavity with a nonlinear up-taper, which further improves the mode purity of the generated output radiation has been proposed and is being currently implemented as a replacement of the existing resonator. The overall operational performance and the output characteristics of this gyrotron (called FU CW III in accordance with the nomenclature adopted at FIR UF Center) make it a versatile and appropriate source of coherent CW radiation for many novel applications in the fields of high-power terahertz science and technologies.

Development and Application of Gyrotrons at FIR UF

The gyrotrons developed at the FIR UF Research Center have stimulated numerous novel applications in the wide field of the high-power terahertz science and technology. The most notable among them are various advanced spectroscopic techniques, materials processing and characterization, plasma physics, and new medical and biological studies. In this paper, we present both the recent evolution and the current status of these radiation sources operating in a broad range from subterahertz to terahertz frequencies.

Theoretical Study on the 1.185-THz Third Harmonic Gyrotron

We discuss how the existing University of Fukui (FIR UF) second harmonic double-beam gyrotron with the operating frequency 0.79 THz can be adopted for operation at the third harmonic. The new gyrotron will operate at the frequency 1.185 THz and will significantly increase the frequency of the dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR) spectrometer. This will allow one to study new bio-molecules.A special attention is payed to the mode competition between the operating $$ {TE}_{3,11}^{+} $$ mode at the third harmonic and the parasitic modes at the second and fundamental harmonics. The operating parameters of the modified gyrotron are U = 20 kV, α = 1.3, I = 0.35 A, and B = 14.60 T and the expected output power about $$ 100\mathrm{W} $$ .

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

In this paper, we present the recent progress in the development of a series of gyrotrons at FIR UF 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 CW regime. Among them are high-precision spectroscopic techniques (most notably DNP-NMR, ESR, XDMR, and studies of the hyperfine splitting of the energy levels of positronium), treatment and characterization of advanced materials, new medical technologies.

Development of THz Gyrotrons at IAP RAS and FIR UF and Their Applications in Physical Research and High-Power THz Technologies

In this paper, we present some of the most significant recent results that characterize the state of the art in the development of sub-THz and THz gyrotrons at IAP-RAS and FIR-UF after 15 years of collaboration as well as their applications in various novel and prospective research fields and advanced technologies.

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

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.