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Isamu Ogawa

Publications and source records attributed to Isamu Ogawa.

3 recordsLinked to original sources

High-Dimensional Bayesian Optimization with Constraints: Application to Powder Weighing

Bayesian optimization works effectively optimizing parameters in black-box problems. However, this method did not work for high-dimensional parameters in limited trials. Parameters can be efficiently explored by nonlinearly embedding them into a low-dimensional space; however, the constraints cannot be considered. We proposed combining parameter decomposition by introducing disentangled representation learning into nonlinear embedding to consider both known equality and unknown inequality constraints in high-dimensional Bayesian optimization. We applied the proposed method to a powder weighing task as a usage scenario. Based on the experimental results, the proposed method considers the constraints and contributes to reducing the number of trials by approximately 66% compared to manual parameter tuning.

cs.LG

Plasma scattering measurement using a submillimeter wave gyrotron as a radiation source

Plasma scattering measurement is effective technique to observe low frequency density fluctuations excited in plasma. The spatial and wave number resolutions and the S/N ratio of measurement depend on the wavelength range, the size and the intensity of a probe beam. A well-collimated, submillimeter wave beam is suitable for improving the spatial and wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N ratio of the measurement because of its capacity to deliver high power. Unlike the molecular vapor lasers, the gyrotrons generate diverging beam of radiation with TEmn mode structure. It is therefore necessary to convert the output radiation into a Gaussian beam. A quasi-optical antenna is a suitable element for the conversion system under consideration since it is applicable to several TE0n and TE1n modes. In order to apply the gyrotron to plasma scattering measurement, we have stabilized the output (P=110W, f=354GHz) of gyrotron up to the level (DP/P<1 %, Df<10 kHz). The gyrotron output can be stabilized by decreasing the fluctuation of the cathode potential.

physics.plasm-ph

Development of submillimeter wave source Gyrotron FU series for plasma diagnostics

Our gyrotrons developed in Fukui University, Research Center for Development of Far Infrared Region (FIR FU) are high frequency, medium power gyrotrons as millimeter to submillimeter wave radiation sources for application to new far-infrared technologies including plasma diagnostics. We have already developed Gyrotron FU Series which consists of 8 gyrotrons. The gyrotron series has achieved frequency tuneability in wide range (from 38 GHz to 889 GHz). The highest frequency is corresponding to a wavelength of 337 micrometers. This is a current record for high frequency operation of gyrotron. Recently, we have developed a high harmonic gyrotron with an axis-encircling electron beam and a THz gyrotron with a pulse magnet. In this presentation, the present status of Gyrotron FU Series is described.

physics.plasm-ph