Development of 394.6 GHz CW Gyrotron (Gyrotron FU CW II) for DNP/Proton-NMR at 600 MHz

Gyrotron FU CW II with an 8 T liquid He free superconducting magnet, the second gyrotron of the THz Gyrotron FU CW Series, has been constructed and the operation test was successfully carried out. It will be used for enhancing the sensitivity of 600 MHz proton-NMR by use of Dynamic Nuclear Polarization (DNP). The designed operation mode of the gyrotron is TE_2,6 at the second harmonic. The corresponding frequency is 394.6 GHz. The real operation frequency is 394.3 GHz at TE₀₆ mode, because of fabrication error of the diameter of the cavity. The operation is in complete CW at the output power of around 30 W or higher at the TE₀₆ cavity mode. There are many other operation modes at the fundamental and the second harmonic. Typical output power of the fundamental and the second harmonic are higher than 100 W and 20 W, respectively. The highest frequency observed up to the present is 443.5 GHz at the second harmonic operation of TE_6,5 mode. The measured results are compared with the theoretical consideration.     

Observation of Mode Patterns for High Purity Mode Operation in the Submillimeter Wave Gyrotron FU VA

Operation tests of a cavity designed for high purity mode operation of the submillimeter wave gyrotron FU VA has been carried out successfully. The observed emission patterns of several cavity modes appear very pure and are compared with calculated results. High purity mode operation has the advantage of making the conversion to Gaussian-like beams more efficient.     

Observation of Mode Patterns for High Purity Mode Operation in the Submillimeter Wave Gyrotron FU VA

Operation tests of a cavity designed for high purity mode operation of the submillimeter wave gyrotron FU VA has been carried out successfully. The observed emission patterns of several cavity modes appear very pure and are compared with calculated results. High purity mode operation has the advantage of making the conversion to Gaussian-like beams more efficient.     

Ti-Containing Silsesquioxane Gels with Tunable Porosity: Preparation and Catalytic Activity for the Epoxidation of Cyclooctene by Aqueous Hydrogen Peroxide

Novel Ti-containing silsesquioxane gel catalysts were prepared by the hydrosilylative condensation of Ti-containing silsesquioxanes together with cubic silsesquioxanes and spherosilicates. The porosity of gels was controlled by changing the composition and the mixing order of the starting materials. Both porous and nonporous gels were found to act as excellent heterogeneous catalysts towards the selective epoxidation of cyclooctene by the use of aqueous hydrogen peroxide as an oxidant.     

Long Pulse Operation of the THz Gyrotron with a Pulse Magnet

Long pulse operation up to 1 msec of a high frequency gyrotron with a pulse magnet has been successfully carried out in a frequency range including 1 THz. In the experiments, the timing of an electron beam pulse injection is adjusted at the top of the magnetic field pulse, where the variation of field intensity is negligible. The operation cavity modes seem to be TE_{1, 12} and TE_4,12 at the second harmonics. The corresponding frequencies are 903 GHz and 1,013 GHz, respectively. Additionally several features of radiation measurement results of the gyrotron are described and brief considerations are presented.     

Development of a Millimeter-Wave Electron-Spin-Resonance Measurement System for Ultralow Temperatures and Its Application to Measurements of Copper Pyrazine Dinitrate

We have developed a millimeter-wave electron-spin-resonance (ESR) measurement system using a ³He-⁴He dilution refrigerator for the ultralow-temperature range below 1 K. The currently available frequency range is 125–130 GHz. This system is based on a Fabry-Pérot-type resonator (FPR) that is composed of two mirrors. The frequency can be changed by adjusting the distance between the mirrors using a piezoelectric actuator installed at the bottom of the resonator. A homodyne detection system with an InSb detector is built into the low-temperature section of the ³He-⁴He dilution refrigerator; this system provides high sensitivity. Using this system, we performed ESR measurements on a Heisenberg quantum-spin chain—copper pyrazine dinitrate, Cu(C₄H₄N₂)(NO₃)₂—over the temperature range from 6.6 down to 0.25 K. The ESR lines change continuously with decreasing temperature. Our results suggest that the ESR spectrum of copper pyrazine dinitrate may be useful as a temperature sensor for the very low-temperature range.     

Development of Millimeter Wave Fabry-Pérot Resonator for Simultaneous Electron-Spin and Nuclear Magnetic Resonance Measurement

We report a Fabry-Pérot resonator with spherical and flat mirrors to allow simultaneous electron-spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements that could be used for double magnetic resonance (DoMR). In order to perform simultaneous ESR and NMR measurements, the flat mirror must reflect millimeter wavelength electromagnetic waves and the resonator must have a high Q value (Q?>?3000) for ESR frequencies, while the mirror must simultaneously let NMR frequencies pass through. This requirement can be achieved by exploiting the difference of skin depth for the two frequencies, since skin depth is inversely proportional to the square root of the frequency. In consideration of the skin depth, the optimum conditions for conducting ESR and NMR using a gold thin film are explored by examining the relation between the Q value and the film thickness. A flat mirror with a gold thin film was fabricated by sputtering gold on an epoxy plate. We also installed a Helmholtz radio frequency coil for NMR and tested the system both at room and low temperatures with an optimally thick gold film. As a result, signals were obtained at 0.18 K for ESR and at 1.3 K for NMR. A flat-mirrored resonator with a thin gold film surface is an effective way to locate NMR coils closer to the sample being examined with DoMR.     

Preparation and the catalytic activity of novel Pd nanocluster catalysts utilizing an oligosilsesquioxane ligand

Palladium acetate together with a newly synthesized silsesquioxane- pyridyl ligand showed excellent catalytic activity towards the aerobic oxidation of benzyl alcohol to benzaldehyde. TEM measurements revealed the in situ formation of Pd nanoclusters during the reaction period.     

Computer Simulation of Axis-Encircling Beams Generated by an Electron Gun with a Permanent Magnet System

Results from computer aided design of a novel electron gun generating axis-encircling beams are presented and discussed. Numerical experiments were performed by the new version of the software package GUN-MIG named GUN-MIG/CUSP. It is based on a self-consistent relativistic model and is developed as a problem oriented tool for analysis of electron-optical systems with magnetron injection guns (MIG) and electron guns with field reversal (cusp guns), forming axis-encircling beams. As a result of the simulations an electron-optical design of a novel electron gun with permanent magnet system was accomplished. The gun is expected to form high quality beams with small velocity spread and beam ripple. Parameters of the generated beams are appropriate for a prospective weakly relativistic high harmonic large orbit gyrotron (LOG). The development of such device is in progress now at the Research Center for Development of Far-Infrared Region (FIR Center) at Fukui University.     

High Power,Frequency Tunable,Submillimeter Wave ESR Device Using a Gyrotron as a Radiation Source

ESR device using a submillimeter wave gyrotron as a radiation source and a pulse magnet for high field up to 30 T has been constructed. Our gyrotrons (Gyrotron FU series) were developed as millimeter and submillimeter wave radiation sources and have attractive advantages for ESR spectroscopy, for example, high power and frequency tunability over broad range. The ESR device has been successfully applied to three cases of ESR measurements. In the first case, the temperature dependence of ESR was measured for a typical antiferromagnetic material MnO at the frequency of 301 GHz. In the second case, the dependence of the fine structure constant of the ruby on the magnetic field intensity was measured in the millimeter to submillimeter wave region. In these two cases, the gyrotron was operated by complete cw mode. In the final case, a pulse technique was applied to the ESR, the gyrotron was operated in pulse mode and the pulsed magnetic field was generated in the synchronized phase with the gyrotron operation.