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Results of H[sub α] measurement in the GAMMA 10 tandem mirror are described, with a particular focus on the behavior of neutrals in the anchor minimum-B region. Recently a set of H[sub α] line-emission detector arrays was designed and installed in the anchor-cell, where the shape of the magnetic flux tube becomes flat and the cross section of plasma is elongated elliptically. The detector consists of H[sub α] interference filter, optical fiber, and photomultiplier with magnetic shield, and is absolutely calibrated by using a standard lamp. In standard ion-cyclotron-range-of-frequency heated, hot-ion-mode plasmas, detailed measurements of H[sub α] line-emission form the central-cell to the anchor-cell were carried out, and the dependence of the H[sub α] intensity on the quantity of gas puffing was investigated. The characteristic behavior of neutrals in the nonaxisymmetric anchor-cell is also discussed, based on the result of neutral transport simulation. [ABSTRACT FROM AUTHOR]

Waves in the ion cyclotron range of frequency are efficiently used to produce and heat magnetic mirror plasmas. In relatively low-density (lower than 10[sup 18]m[sup –3]) plasmas, the fast Alfvén eigenmodes are formed in radial and axial directions and the excitation of these modes is strongly affected by the density. The slow Alfvén waves are also effectively used for plasma heating. The ion temperature above 10 keV is achieved, which is confirmed by the detection of fusion neutrons. The excitation of Alfvén eigenmodes is studied in the GAMMA 10 tandem mirror. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The improvement of potential confinement was attained in the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985); Proceedings of the 13th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Washington, 1990 (Intemational Atomic Energy Agency, Vienna, 1991), Vol. 2, p. 539] by axisymmetrization of heating systems for the plasma production, heating, and potential formation. A significant increase of the density and diamagnetism by the potential confinement was observed. In the previous experiment, it was difficult to increase the central cell density higher than 2.7 × 10[sup 18]m[sup -3] One of the possible mechanisms is the density clamping due to the eigenmode formation ofthe ion-cyclotron-range of frequency (ICRF) waves in the axial direction. With high harmonic ICRF waves (RF3), the experiments to overcome this problem have been performed. In preliminary experiments with RF3 and NBI the maximum density of 4x 10[sup 18]m[sup -3] was attained. [ABSTRACT FROM AUTHOR]

Performs charge-exchange neutral particle measurements on electron cyclotron resonance heating experiments in hot-ion-mode plasmas of the GAMMA 10 tandem mirror. Description of the experimental apparatus; Temporal behavior of plasma parameters; Evaluation of ion-energy losses; Estimation of ion temperature.

Alfvén ion-cyclotron wave excited in the central-cell plasma of the GAMMA 10 tandem mirror is investigated by a reflectometer system. The Fourier amplitude of the instability strongly depends on the anisotropy of the ion velocity distribution function and the plasma β value. The ratio 0.2–0.3 between O-mode and X-mode reflectometer signals suggests that a magnetic fluctuation level similar to the density fluctuation level is excited in the plasma due to the instability. [ABSTRACT FROM AUTHOR]

A wide-band radio-frequency (rf) probe system was constructed for the active diagnostic of the eigenmode formations in the ion-cyclotron range of frequency (ICRF) in GAMMA10. An antenna was installed in the peripheral region in the central cell. The low power rf pulse with the frequency sweep is applied to the antenna. The waves excited in the plasma are detected with a magnetic probe. The excitation of eigenmodes is described by using the antenna-plasma-probe transfer function. The transfer function can be obtained from the antenna current signal and the magnetic probe signal. When the real and imaginary parts of the transfer function are plotted on the complex plane, the resultant curves are approximately circular, indicating an eigenmode formation. The results of the measurement show that several eigenmodes can be excited in the present experimental condition. [ABSTRACT FROM AUTHOR]

High beta plasmas in the anchor cell of the GAMMA 10 tandem mirror are formed by using a fundamental ion cyclotron resonance heating. Because the closed resonance surface exists near the midplane of the anchor cell, strongly peaked profile of the plasma pressure will be formed. To measure the axial profiles of the ion temperature and density, a time-of-flight type neutral-particle analyzer (TOF–NPA) has been developed. TOF–NPA can detect neutral particles and photons separately at the same time. The ion temperature and density have been evaluated from the particle and photon signals, respectively. The peaked profile of the ion temperature within the closed resonance surface has been confirmed. [ABSTRACT FROM AUTHOR]

Low frequency fluctuations of a plasma in the central cell of the GAMMA10 tandem mirror have been observed with electrostatic probes (ESPs) installed at the peripheral region of the plasma. Typical plasma parameters for a hot ion mode operation are ne∼2×1012 cm-3, Ti∼4 keV, Te∼100 eV, B=4 kG, and rp=18 cm. Although the ESP is an effective tool to measure local plasma parameters and fluctuations, it can be damaged with the higher electron temperature. Here, a new visible light detector was introduced, which could measure the plasma fluctuations without contacting the plasma. The obtained results were compared with those of ESPs. It is found that the visible light detector is applicable when the electron temperature becomes much higher in the future experiment. [ABSTRACT FROM AUTHOR]

The beam deflection coefficients to the magnetic field fluctuation using a gold neutral beam probe was examined by numerical simulations. The beam deflection parallel to the magnetic field line was mainly caused by the azimuthal component of the magnetic field fluctuation in a case of the beam passing through the plasma center; on the other hand, the beam passing through the plasma edge was deflected by the radial component of the magnetic field fluctuation because the radial and azimuthal velocity components of the beam depend on the injection angle into the plasma. Then, the coefficients could be described as being the function of the injection angle which indicated the radial position of the ionization point and the measured point. As a result of numerical simulation, the coefficients were estimated to be 0.1 and 1.3 for the radial and the azimuthal components of the magnetic field fluctuation in the case of the beam passing through the plasma center. We also estimated the potential effects on the beam deflection parallel to the magnetic field line by the numerical simulation because the change of the beam energy caused the beam detected point to move. We found the potential effects to be smaller than the sensitivity of the magnetic field fluctuation. [ABSTRACT FROM AUTHOR]

An ion sensitive probe (ISP) has been applied to ion diagnostics of the edge plasma of the GAMMA10 tandem mirror device. Since high energy ions are created by ion cyclotron range of frequency heating in the central cell of GAMMA10, a secondary electron repeller electrode is set in to suppress secondary electrons emitted from the collector due to high energy ions. Then secondary electrons are successfully suppressed. The ion flux flowing into the collector is evaluated with numerical calculation of ion orbits. This calculation includes the potential profile near the tip of the ISP. Then a correction factor Fα of the ion flux to the free streaming one is determined. The calculation yields V–I characteristic of the collector current. The ion density can be estimated by using the measured ion temperature and the factor Fα. Sample data of the ion temperature and the ion density in the edge region of the central cell of GAMMA10 are given. The measurement with the ISP shows that the edge ion temperature of GAMMA10 plasma ranges from 100 to 400 eV, and the ion density from 0.5×1010 to 2×1010 cm-3. [ABSTRACT FROM AUTHOR]

In order to passivate deep levels, hydrogen was introduced into 3C-SiC by a hydrogen plasma treatment. The effects of hydrogen were investigated by deep level transient spectroscopy (DLTS). DLTS results indicated that hydrogen passivates deep levels in the as-grown sample. However, the results also indicated that the plasma treatment simultaneously forms deep levels originated from damages in the surface region. In order to suppress the damages, we introduced a grid between the sample and the plasma source during the plasma treatment. DLTS results showed that the grid reduces the deep levels originated from the damages, retaining the hydrogen passivation effects. The defect concentration is less than 1014 cm−3 for the sample treated by the hydrogen plasma with the grid and subsequently annealed at 300 °C. [Copyright &y& Elsevier]

This paper describes the results of the experiments performed on Tandem Mirror device GAMMA 10/PDX mainly using a new “divertor simulation experimental module (D-module)” installed on one of the end mirror exits which is specially designed to investigate the physics of plasma detachment. The additional ICRF heating in the anchor-cells, connected to both ends of the central-cell, significantly increases the density in the both cells, which attained the generation of the highest particle flux up to 10 23 particles/s m 2 at the end-mirror exit. H 2 and noble gas injection to enhance the radiation cooling in D-module was performed and a remarkable reduction of the electron temperature (from few tens eV to <3 eV) on the target plate were successfully achieved associated with the strong reduction of particle and heat flux. A significant effect of simultaneous injection with hydrogen and noble gases for detached plasma formation was recognized for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen recycling has been studied focusing on the neutral behavior in front of tungsten target in the plasma–wall interaction simulator APSEDAS and the tandem mirror GAMMA 10. The line intensity of hydrogen Balmer series decreased toward the target corresponding to a decrease in the electron density in APSEDAS. The relative population of n =3 and n =4 increased and that of n =5 and n =6 decreased just in front of the target (Z <5mm). This might be attributed to the reflected atom or reemitted molecule from the target. In GAMMA 10, the intensity of hydrogen Balmer (Hα) line decreased exponentially with distance from the target with two decay lengths: ∼16mm and ∼53mm. These two short decay lengths are attributed to the fact that a fraction of the reflected atoms and atoms dissociated from molecules are at excited energy states. [Copyright &y& Elsevier]