Observation of the Effects of Radially Sheared Electric Fields by the Use of a Gold Neutral Beam Probe

Plasma and Fusion Research

Mizuguchi

et al. 2010

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.

Section: Introductionmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of Fluctuation Suppression during Potential Formation in the Tandem Mirror GAMMA 10

Plasma and Fusion Research

Mizuguchi

et al. 2010

“…The plasma is produced by plasma guns and is heated and sustained using ion cyclotron range of frequency (ICRF) heating systems. The plug/barrier cells are located at both ends of GAMMA 10, where the ion and electron axial confinement potentials are produced by electron cyclotron resonance heating.Density and potential fluctuations are measured by a gold neutral beam probe (GNBP) system [5][6][7]. The probe beam is neutral gold particles.…”

mentioning

confidence: 99%

“…Density and potential fluctuations are measured by a gold neutral beam probe (GNBP) system [5][6][7]. The probe beam is neutral gold particles.…”

mentioning

confidence: 99%

Correlation between Low-Frequency Fluctuations and Plasma Stored Energy in GAMMA 10

Plasma and Fusion Research

Yaguchi

et al. 2010

The instabilities observed in many magnetic confinement devices induce radial particle transport. Density and potential fluctuations were measured using a gold neutral beam probe in GAMMA 10. The plasma stored energy repeatedly increases and decreases during ion-cyclotron range of frequency heating. A drift-type fluctuation was observed in both the density and the potential as the plasma stored energy decreased. These results indicated a correlation between the radial particle transport induced by drift-type fluctuations and decreasing plasma stored energy. In magnetically confined plasmas, particle and energy confinement are important because particle transport decreases the density and temperature. The plasma particles escape across the confinement magnetic field as a result of fluctuations due to instabilities in the plasma, which cause fluctuations that lead to the transport [1]. Drift waves, called universal instability, have been observed in many devices because of the plasma density gradient [2-4]. Therefore, it is important to study the mechanisms of particle transport due to fluctuations. In this paper, we present a correlation between low-frequency fluctuations and the plasma stored energy in the GAMMA 10 tandem mirror.Experiments were conducted in the GAMMA 10 tandem mirror. The lengths of the central, anchor, and plug/barrier cells are 6.0, 4.8, and 2.5 m, respectively. The magnetic field strength at the mid-plane of the central cell is 0.41 T in standard operation. The plasma is produced by plasma guns and is heated and sustained using ion cyclotron range of frequency (ICRF) heating systems. The plug/barrier cells are located at both ends of GAMMA 10, where the ion and electron axial confinement potentials are produced by electron cyclotron resonance heating.Density and potential fluctuations are measured by a gold neutral beam probe (GNBP) system [5][6][7]. The probe beam is neutral gold particles. The energy and incident angle of the primary beam passing the plasma center are about 12 keV and 40 • to the horizontal direction, respectively. A typical primary beam current of 2 µA is confirmed from a Faraday cup measurement. A parallelplate-type electrostatic energy analyzer with an incident angle of 45 • to the ground plate is installed. In the analyzer, a micro-channel plate detector with 32 anodes de- After the plasma is initiated with both sides of the plasma gun, ICRF heating systems are used in the central cell. Figure 1 shows the line-integrated electron density and diamagnetism in the central cell. The diamagnetism indicates the plasma stored energy. The line-integrated electron density fluctuated substantially at 122, 130, 138, and 145 ms, and the diamagnetism decreased at the same time. The diamagnetism repeatedly increases and decreases during the ICRF heating period. The density and potential fluctuations were measured at R ∼ 0.01 m using a GNBP. Figures 2 (a) and 2(b) show contour plots of the frequency spectra of the density and potential fluctuation levels, respectively, obtained by ti...

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

Review of Scientific Instruments

Oono

et al. 2008

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.