Millimeter Wave ESR Using Gyrotron as a Light Source

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Spectroscopic studies have not been so active in millimeter wave region mainly due to the lack of available light sources. In this project, the gyrotron developed for the plasma heating and diagnosis was utilized as the light source of the millimeter wave ESR.A gyrotron with small size electron gun and high Q cavity was designed and manufactured for ESR spectrometer of W and D bands. In spite of many accidents such as air leakage of the cryostat for the superconducting magnet, trouble of the power supply of the superconducting magnet and damage of the high voltage transformer, the developed gyrotron was proved to yield strong radiation of 93.9GHz-146.2GHz in W and D bands available for ESR. Some modes of oscillation may be excited continuously with attainable low cathode current as much as lOOmA.ESR in millimeter wave region has been mostly observed by the absorption during transmission, but the present system utilizes Fabry-Perot resonator for the precise measurements in W and D bands … More . For the preliminary test, a backward oscillator, instead of gyrotron, was used to observe ESR spectra at room temperature of some low dimensional lattice antiferromagnets together with a reference spectrum of DPPH. The obtained powder patterns with anisotropic g-factors are highly resolved compared with X band spectra of the same specimens. In the present spectrometer, the mirror spacing of the Fabry-Perot resonator is adjusted finely by applying an AC modulated voltage to a ferroelectric actuator. The coherent output of the detector with the modulation is fed back to the driver of the actuator so as to maintain the resonance condition of the resonator to exclude the dispersion component from the obtained absorption spectra. The software to display the processed signal in real time and to record in the memory of computer is ready for use.Thus, the millimeter wave ESR apparatus with light source of a gyrotron is near the completion. With the apparatus well resolved ESR spectra in W and D bands will be soon obtained after the high voltage transformer of the gyrotron will be repaired. Less