A yttrium-aluminum-garnet Thomson scattering (TS) system was constructed and applied to the tandem mirror GAMMA 10 plasma to measure the electron temperature. A large solid-angle TS light-collection system was set using a spherical mirror system and a large numerical aperture of bundled optical fiber. A five-channel polychromator with avalanche silicon photo diodes was employed after being calibrated with standard light. Calibration was performed by Rayleigh and Raman scattering. An electron temperature increase from 40 eV to 80 eV was observed with application of electron cyclotron heating to plug/barrier cells. GAMMA 10 is the world largest tandem mirror machine with which plasma confinement is achieved not only by a magnetic mirror configuration but also high potentials at both end regions [1][2][3]. The main plasma is produced and heated by ion-cyclotron range of frequency waves. The confinement potentials are produced by plug and barrier electron cyclotron heating (P/B-ECH) at the plug/barrier regions. During the formation of confinement potential, the typical electron density, electron temperature, and ion temperature are about 2 × 10 18 m −3 , 0.1 keV, and 5 keV, respectively. Thomson scattering (TS) is the most reliable diagnostic for measuring electron temperature and electron density. In GAMMA 10, a ruby-laser TS system was installed to measure the electron temperature. However, the system experienced problems. Previously, electron temperature has been measured by soft X-ray measurement. Thus far, direct electron heating by ECH experiments have been conducted in the central cell. In addition, density and potential fluctuation suppressions during the formation of confinement potential have been studied using a gold neutral beam probe system [1][2][3]. After the aforementioned problems with the ruby-laser TS system, we planned to install a neodymiumdoped, yttrium-aluminum-garnet laser (Nd:YAG) TS system to measure electron temperature directly in the central cell of GAMMA 10. In comparison with the ruby-laser author's e-mail: yosikawa@prc.tsukuba.ac.jp system, operation of the YAG laser system is easier and the repetition rate of such a system is much larger. The YAG TS system is normally used in higher electron density plasmas, over 10 19 m −3 . Moreover, an efficient TS system is necessary to measure low-density plasmas in the region of less than 10 19 m −3 , such as the GAMMA 10 plasma and the peripheral plasma of high-density fusion plasmas. To obtain a TS signal with a good signal-to-noise ratio, we developed an optical-collection system with a large solid angle. In this paper, we describe the newly installed YAG TS system and the first results of electron temperature and density measurements in the tandem mirror GAMMA 10. The YAG TS system is constructed with laser, incident optics, light-collection optics, signal-detection electronics, and a data-recording system. A 10-Hz Nd:YAG laser (Continuum, Powerlite 9010) with an energy per pulse of 2 J, a pulse width of about 10 ns, and operating at a fund...

An yttrium-aluminium-garnet (YAG) Thomson scattering (TS) system was constructed and applied to the tandem mirror GAMMA 10 device to measure the electron temperature and density. A large solid-angle TS light-collection system was achieved by use of a spherical mirror system and large numerical aperture of bundled optical fiber. A five-channel polychromator with avalanche silicon photo diodes was used. Calibration experiments for TS optical system were performed by Rayleigh and Raman scatterings. An electron temperature increases from 0.04 keV to 0.09 keV was observed with application of electron cyclotron heating (ECH) in the plug/barrier (P/B-) cells. We successfully obtained the radial electron temperature profiles without and with P/B-ECH.

In the tandem mirror GAMMA 10, plasma confinement is achieved by not only a magnetic mirror configuration but also high potentials in both end regions. Before plug electron cyclotron resonance heating (P-ECH) was applied, drift-type fluctuations were observed in potential and density measurements. Potential and density fluctuation suppression during potential formation by the application of P-ECH was clearly observed using a gold neutral beam probe (GNBP) system. We study the relationship between the suppression levels of potential fluctuations and the effects of the produced potentials by varying the applied ECH power. Moreover, the particleflux-related values obtained by the phase difference between the potential and density fluctuations are measured using the GNBP. We can clearly show that radial anomalous transport induces radial particle transport, which decreases the plasma stored energy.

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The physical mechanisms of the improvement of plasma confinement due to the formation of electrostatic potential and electric field were studied. A 12-keV gold neutral beam probe (GNBP) with the same capabilities as a heavy ion beam probe was operated on the GAMMA 10 tandem mirror. The simultaneous multipoint system was developed to measure the local electric field. The structure of the novel analyzer and the technique for measuring the local electric field were studied by using the calculation code of three-dimensional beam trajectory. It was possible for the first time to measure the local electric field in a single plasma shot by the simultaneous multipoint plasma potential measurement system using the GNBP in the GAMMA 10 tandem mirror. Fluctuations caused by instabilities in plasmas are observed in some magnetic confinement devices [1][2][3]. It is quite important to study plasma particle transport across the confinement magnetic field caused by fluctuation. In the GAMMA 10 tandem mirror, the electrostatic and magneto-hydrodynamic fluctuations were measured and were found to be related to radial transport [4,5]. In addition, a decrease in the plasma stored energy due to the radial transport was also observed.The physical mechanisms of the plasma confinement improvement due to the formation of electrostatic potential and electric field were studied [6,7]. A beam probe is a useful tool in terms of the energy conservation of a heavy ion beam for potential and fluctuation measurements. A gold neutral beam probe (GNBP) with same capabilities as heavy ion beam probes is operated on the GAMMA 10 tandem mirror [8][9][10]. Figure 1 shows a schematic view of the GNBP system. The energy and incident angle of the neutral beam that pass the plasma center are about 12 keV and 40 degrees to the horizontal direction, respectively. The typical negative ion beam diameter and current intensity are 5 mm and 2 µA, respectively, as measured by a Faraday Cup detector. The gold positive ion beam produced in collisions with plasma electrons is analyzed by parallel-plate type electrostatic energy analyzer with the incident angle of 45 degree to the ground plate. The width and length of the current slit are 0.7 and 12 mm, respectively. The positive ion beam is detected by a micro-channel plate (MCP) with 32 anodes. The width and length of each anode are 2.4 and 31 mm, respectively.It is difficult to measure the local electric field with author's e-mail: miyata.yoshiaki@jaea.go.jp high precision. Previously, two measuring techniques were used to measure the radial potential profile and electric field in the core plasma. In the first measuring technique, the measuring position is changed by the deflecting beam trajectory for each shot. This measuring technique has high time resolution; however, the calculation of radial electric field has a large error induced by the poor reproducibility of the plasma shot. Another measuring technique involves changing the measuring position by sweeping the applied choppy voltage to the deflecting plat...