Fumiaki Yaguchi

Use of a Gold Neutral Beam Probe to Study Fluctuation Suppression During Potential Formation in the GAMMA 10 Tandem Mirror

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

Radial electron temperature measurements by using newly installed Thomson scattering system in GAMMA 10

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.

Status and Plan of GAMMA 10 Tandem Mirror Program

Abstract Recent progress and near future plan of GAMMA 10 efforts are presented. With high power plug electron cyclotron heating (ECH) up to ~400 kW, the ion confining potential of more than 2 kV was confirmed. The drift type low frequency fluctuations were suppressed by the positive radial electric field produced by plug ECH. It is found that the efficient EC heating on mirror devices from a strong B field side requires the minimization of the stray microwave in addition to the 100% X-mode excitation to avoid the enhancement of the ion loss. The development of a gyrotron, the key tool of these ECH experiments, has been made in collaboration with NIFS (National Institute for Fusion Science), More than 1.5 MW for more than 1s has been demonstrated at 77GHz. The plan of the boundary plasma research program with modification of GAMMA 10 is in progress. The new program includes the physics and technology studies of the divertor and SOL plasmas and PWI relevant to torus plasmas like ITER. The high heat flux experiments using the open end mirror throat has been started and we have obtained successful preliminary data, which include the heat flux of 8 MW/m2.

Fluctuation Suppression during Confinement Potential Formation in GAMMA 10

Abstract The suppression of the potential fluctuation was clearly observed by a gold neutral beam probe (GNBP) during the higher potentials and positive electric fields driven by electron cyclotron heating. The particle flux evaluated from the phase difference between the potential and density fluctuations measured by GNBP showed the radial outward flux and correlates with the decrease in the stored energy. When flux is suppressed by the potential formation, the quick plasma stored energy increase is observed.

Observation of the Flute-Type Fluctuation by Using the Gold Neutral Beam Probe in Gamma 10

Abstract In magnetic nuclear fusion plasmas, plasma particle transport causes the decrease of density and stored energy. Plasma particle and thermal energy are lost across the confinement magnetic field lines by the turbulence of thermodynamics force and instability. We studied the characteristics of flute-type fluctuation by using the gold neutral beam probe (GNBP) and electrostatic probes.