Youhei Oono

Upgrade of the analyzer design for multipoint measurements by a gold neutral beam probe on the GAMMA 10 tandem mirror

The study of the mechanisms of both transport and fluctuations is one of the main issues of fusion plasma researches. Spatial fluctuation structure measurements are important for studying of cross correlation between the two fluctuations. Gold neutral beam probe systems are used in GAMMA 10 tandem mirror plasma device. Currently, the plasma potential and its fluctuations cannot be measured at different radial positions simultaneously. This paper presents the upgrade design of the 45 degrees electrostatic energy analyzer for the simultaneous multipoint measurements of plasma parameters.

Study of radial potential fluctuations by using a gold neutral beam probe system.

A study of fluctuation is one of the main issues in fusion plasma researches. The potential and its fluctuation are measured by a gold neutral beam probe (GNBP) in the tandem mirror GAMMA10. Since there is no stable isotope ((197)Au approximately 100%), there are little measurement errors. GNBP system can measure the potential with about +/-30 V of error. The time and spatial resolutions are estimated to be about 3 micros and 5 mm, respectively. During the formation of axial confining potentials, the radial profiles of the potential and its fluctuation were successfully measured in GAMMA10. GNBP is a useful tool for the study of radial potential fluctuation directly in plasmas.

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.

Study of Radial Particle Flux Due to Phase Difference Between Potential and Density Fluctuations

Abstract There is a radial particle transport as the loss induced by the fluctuations. It is possible to measure the potential and density fluctuations at the arbitrary point simultaneously by using gold neutral beam probe, and their phase difference between them. The radial particle transport induces the decreasing of the plasma stored energy. This phenomenon is estimated the theoretically-predicted loss process induced by the radial transport due to the phase difference between the potential and density fluctuations.

DENSITY FLUCTUATION MEASUREMENTS IN THE TANDEM MIRROR GAMMA-10

Abstract Considerable interests have been focused on the study of turbulent fluctuations in magnetic confinement system, since various theories predict such turbulent fluctuations lead to anomalous transport and energy loss in the transverse direction. Density fluctuations during the formation of the confinement potential with application of electron cyclotron heating (ECH) in GAMMA 10 were studied by using both the multi-channel microwave interferometer and gold neutral beam probe. It is found that low frequency fluctuation, which corresponds to the diamagnetic drift, is suppressed during the formation of confining potential by the application of plug-ECH.

RADIAL POTENTIAL FLUCTUATION MEASUREMENTS DURING THE APPLICATION OF ELECTRON CYCLOTRON HEATING IN THE TANDEM MIRROR GAMMA 10

Abstract A study of fluctuation is one of main issues in fusion plasma researches. In the tandem mirror GAMMA10, a potential fluctuation changes during the formation of confinement potential with the application of electron cyclotron heating (ECH). Potential fluctuation induces radial particle transports. We have studied the radial profiles of the potential fluctuation during the application of ECH. The potential in the central cell of GAMMA10 is measured by a gold neutral beam probe (GNBP) system. GNBP is a useful tool for the study of radial potential and its fluctuation directly in the fusion plasmas. It was confirmed that the stronger radial potential was formed during the application of plug ECH than that without plug-ECH.