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A Ku-band (12–18 GHz) multichannel Doppler reflectometer (DR) has been developed in the GAMMA 10/potential control and divertor simulating experiment (PDX) tandem mirror device to improve the applicability of DR measurement for simultaneous monitoring of velocity of electron density turbulence at different locations. Our previous single-channel DR circuit has been replaced by the multichannel microwave system using a nonlinear transmission line based comb generator with heterodyne technique. The multichannel DR system has been installed in the central cell of GAMMA 10/PDX. Initial results of application to GAMMA 10/PDX plasma are presented, showing Doppler frequency shifts during an additional ion cyclotron resonance frequency heating and gas-puffing experiment. [ABSTRACT FROM AUTHOR]

A divertor simulation experimental module (D-module) in the tandem mirror GAMMA 10/PDX was used for the study of plasma detachment. In previous studies, it was difficult to measure far-upstream plasma parameters in the D-module, and only electrostatic probes on the target plate were used to perform electron temperature and density measurements. To study the detached plasma structure, a Thomson scattering (TS) system and a microwave interferometer system have been installed to measure the inside plasma parameters of the D-module, and a movable electrostatic probe has been placed at the inlet of the D-module to measure the inlet plasma density and temperature. The TS system in the central cell observed the electron temperature and density of the core plasma simultaneously. These measurements revealed the entire density and temperature structure from the core plasma to the divertor plate. The line average electron density measured by the microwave interferometer showed a rollover behavior during detachment. The results indicated that the ionization region was located around the center of the D-module, and it appears to move upstream along the axis. [ABSTRACT FROM AUTHOR]

The pellet ablation mechanism is an interesting subject for plasma fuelling in fusion plasmas. In GAMMA 10/PDX, pellet injection experiments for higher density plasma production are planned to conduct detached plasma experiments in the higher density plasma condition. We measured the pellet ablation cloud by using the two-directional simultaneous photography system in GAMMA 10/PDX. The tomography reconstruction technique was used for considering the pellet trajectory in the plasma and pellet ablation. The three-dimensional pellet trajectory and pellet ablation images in the plasma were clearly obtained for the first time, to the best of our knowledge. [ABSTRACT FROM AUTHOR]

In conventional multichannel/imaging microwave diagnostics of interferometry, reflectometry, and electron cyclotron emission measurements, a local oscillator (LO) signal is commonly supplied to a receiver array via irradiation using LO optics. In this work, we present a 60-GHz interferometer with a new eight-channel receiver array, called a local oscillator integrated antenna array (LIA). An outstanding feature of LIA is that it incorporates a frequency quadrupler integrated circuit for LO supply to each channel. This enables simple and uniform LO supply to the receiver array using only a 15-GHz LO source and a coaxial cable transmission line instead of using an expensive 60-GHz source, LO optics, and a waveguide transmission line. The new interferometer system is first applied to measure electron line-averaged density inside the divertor simulation experimental module (D-module) on GAMMA 10/PDX tandem mirror device. [ABSTRACT FROM AUTHOR]

Effects of neutron irradiation on X-ray energy responses of silicon semiconductor detectors have been investigated. Neutron irradiation experiments were carried out for n-type photodiode arrays utilized in the Joint European Torus (JET) using deuterium (D) beam-injection into a tritium (T) target for a well-calibrated deuterium–tritium (D–T) fusion neutron production at the Fusion Neutronics Source (FNS) facility of Japan Atomic Energy Research Institute. X-ray energy responses of these detectors are characterized before and after irradiation by the use of synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory of High Energy Accelerator Research Organization (KEK). A recovery of the degraded X-ray energy response after the neutron irradiation has been found at fluences beyond around 1013 neutrons/cm2. A further novel finding is followed as a “re-degradation” by a neutron irradiation level over about 1014 neutrons/cm2. This “non-linear response” may be physically interpreted in terms of a type inversion from n- to p-type silicon in the detectors. Long-term observations of X-ray energy responses of the detectors after neutron irradiation have also been made in order to clarify the “annealing effect”. [Copyright &y& Elsevier]

Under the international fusion cooperating research, ³He neutron detectors in the GAMMA 10 tandem mirror are calibrated by the use of a [sup 252]Cf spontaneous fission neutron source (8.96 × 10[sup 4]n/s). The calibration experiments are carried out with a "rail system" placed along the magnetic axis of the GAMMA 10 central-cell region, where hot ions in the plasma experiments with the bulk temperatures of ∼10 keV are produced. As compared to a previous neutron monitoring system with a BF[sub 3] detector in GAMMA 10, the present ³He systems are designed with about two orders-of-magnitude higher neutron-counting efficiency for analyzing a neutron emissivity from the plasmas in a single plasma discharge alone. Two ³He systems are installed near the middle and the end of the central cell so as to identify the central-cell hot-ion axial profile. The filling pressure of ³He, the effective length, and the diameter of the detector are designed as 5 bar, 300 mm, and 50 mm, respectively. The detector output spectra are carefully analyzed by the use of a preamplifier, a shaping amplifier, as well as a multichannel analyzer for each ³He detector. In the present article, the neutron-counting data from the two ³He detectors due to the on-axis [sup 252]Cf scan are interpreted in terms of the d[sup -2] intensity dependence (d being the distance between the detector and the neutron source) as well as the effects of the central-cell magnetic coils and the other machine structural components. [ABSTRACT FROM AUTHOR]

The effects of nuclear fusion produced neutrons on the X-ray energy responses of semiconductor detectors are characterized. The degradation of the response of position-sensitive X-ray tomography detectors in the Joint European Torus (JET) tokamak is found after neutron exposure produced by deuterium–deuterium and deuterium–tritium plasma fusion experiments. For the purpose of further detailed characterization of the neutron degradation effects, an azimuthally varying-field (AVF) cyclotron accelerator is employed using well-calibrated neutron fluence. These neutron effects on the detector responses are characterized using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory (KEK). The effects of neutrons on X-ray sensitive semiconductor depletion thicknesses are also investigated using an impedance analyser. Novel findings of (i) the dependence of the response degradation on X-ray energies as well as (ii) the recovery of the degraded detector response due to the detector bias application are found and interpreted by systematically combined methods using a synchrotron facility, a cyclotron facility, a fusion plasma device, material analysis methods along with our recent theory on semiconductor X-ray responses. [Copyright &y& Elsevier]

For the purpose of investigating fusion-produced neutron effects on semiconductor x-ray detectors, detection characteristics of x-ray tomography detectors used before and after deuterium–tritium (DT) and/or DD fusion-plasma experiments in the Joint European Torus (JET) tokamak are studied using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory. Degradations in the responses after neutron exposure into the detectors are found to have functional dependence on x-ray energy. Changes in the depletion thicknesses of the detectors are investigated by means of impedance analyses. The Fusion Neutronics Source (FNS) facility of the Japan Atomic Energy Research Institute is also employed for well calibrated DT fusion-produced neutron irradiation onto these semiconductor x-ray detectors. Recovery of the response degradation is found due to a method for supplying the operational bias to the degraded detector. Our theory is applied to interpret these detector characteristics under the irradiation of DT fusion-produced neutrons in the JET tokamak and the FNS facility. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the development of a matrix-type semiconductor x-ray detector for the purpose of determining measurements of temporally and spatially resolved electron temperatures during a single plasma shot. Specifications for the semiconductor detector; Testing of the device in the GAMMA 10 tandem mirror; Achievement of plasma profiles.

Investigates the effects of fusion-produced neutrons on the x-ray responses of semiconductor detectors for x-ray tomography in the Joint European Torus tokamak and the GAMMA 10 tandem mirror. Neutron effects on the x-ray energy responses; Investigation of the changes in the material properties of the detectors using an impedance analyzer.

The quantum efficiency of an ultralow-energy-sensitive pure-Ge (ULE Ge) detector is investigated using synchrotron radiation from the storage ring at AIST especially for x-ray pulse-height analyses (PHAs), down to a few hundred eV. Several types of x-ray diagnostics such as x-ray PHA, x-ray absorption methods, and x-ray tomography using the ULE Ge detector, a NaI(Tl) detector, as well as a microchannel-plate tomography system are employed for investigating electron distribution functions and electron temperature profiles with preliminary central electron-cyclotron heating in the central cell of the GAMMA 10 tandem mirror. These measurements play an important role in studying an essential physics scaling of the electron temperature as a function of electron confining potential in tandem mirror plasmas. [ABSTRACT FROM AUTHOR]

Experimental verification of the effects of radially sheared electric-field (or potential) formation in plasmas is one of the most critical issues to understand the physics basis for plasma confinement improvements. In the GAMMA 10 tandem mirror, recent experimental results show shear formation effects on the suppression of not only coherent drift waves but turbulence-like fluctuations without any coherent phasing relation during the ion-confining potential formation period. Contours of the central-cell soft x-ray brightness show spatially and temporally fluctuated structures during a weak sheared period by the use of the 50 channel microchannel plate system. A new x-ray tomography system is developed for analyzing temporally and spatially resolved plasma behavior in the presence or absence of these shear formation effects in GAMMA 10. The system consists of two 48-channel silicon semiconductor detector arrays with different viewing angles. X-ray energy responses of the new detector arrays along with response uniformity of detector channels have been characterized using synchrotron radiation at the Photon Factory. [ABSTRACT FROM AUTHOR]

Reports on the first experimental verification of the three-dimensional diffusion effect of x-ray-produced charges in semiconductor x-ray detectors on the quantum-efficiency enhancement. Description of the positron storage ring, monochromator, and detectors used in the experiments; Relation between the x-ray-beam position and the multichannel-detector location.

Investigates the detection characteristics of an ultralow-energy measurable pure-germanium detector in the hundreds-eV photon-energy region. Description of the experimental setup; Output current from each detector; X-ray response for high-energy x rays; Detection-efficiency data.

A new interferometer is installed on the west anchor cell of the GAMMA 10 tandem mirror. In GAMMA 10, we have used a heterodyne-type interferometer with a 70-GHz IMPATT oscillator and a 150-MHz oscillator for frequency modulation. The new interferometer consists of a 17.5-GHz phase locked dielectric resonator oscillator and a 37.5-MHz temperature-compensated crystal oscillator, as well as frequency multipliers. The main motivation for the new interferometer using frequency multipliers is to achieve a stable and cost effective interferometer. Direct anchor heating experiments with new anchor ion cyclotron range of frequency antennas in both the west and the east anchor cells are carried out. Density increases in both anchor cells are clearly observed using the new interferometer. [ABSTRACT FROM AUTHOR]

Doppler-backscattering (DBS) has been used in several fusion plasma devices because it can measure the perpendicular velocity of electron density perturbation v⊥, the radial electric field Er, and the perpendicular wavenumber spectrum S(k⊥) with high wavenumber and spatial resolution. In particular, recently constructed frequency comb DBS systems enable observation of turbulent phenomena at multiple observation points in the radial direction. A dual-comb microwave DBS system has been developed for the large helical device plasma measurement. Since it is desirable to control the gain of each frequency-comb separately, a frequency-comb DBS system was developed with a function to adjust the gain of the scattered signal intensity of each channel separately. A correction processing method was also developed to correct the amplitude ratio and the phase difference between the in-phase and quadrature-phase signals of the scattered signals. As a result, the error in Doppler-shift estimation required to observe vertical velocity and the radial electric field was reduced, which enables more precise measurements. [ABSTRACT FROM AUTHOR]

Abstract: Tomographic reconstructions of X-ray emission from hot electrons having a temperature of several tens of keV and cold electrons having a temperature ranging below 100eV have been carried out by the use of the novel position-sensitive X-ray diagnostic system. The X-ray detection system in the thermal-barrier region of the GAMMA 10 tandem-mirror plasmas consists of a 48-channel silicon semiconductor detector array and the 50-channel microchannel plates (MCPs). When we make outward shifts of the second-harmonic electron cyclotron layers radially by intensifying the mirror magnetic fields in the thermal-barrier region, tomographically reconstructed signals by using the MCP show hollow X-ray profiles and the X-ray reconstructed signals obtained with the semicondcutor detector indicate a good axisymmetric radial profile peaked on the magnetic axis. Several applications including investigation of these hot electrons due to the second-harmonic electron cyclotron heating are made with the newly developed X-ray diagnostic systems. [Copyright &y& Elsevier]

Temporally and spatially resolved X-ray analyses are carried out by using novel matrix-type X-ray semiconductor detector arrays in the GAMMA 10 tandem mirror. The detector array has seven “matrix columns” for the measurements of plasma X-ray profiles so as to make X-ray tomographic reconstructions. Further, six “matrix rows” having various dead layer thicknesses are fabricated as “unbreakable ultra-thin X-ray absorption filters” for simultaneous analyses of six different X-ray energy ranges. The characteristics of the detector array make it possible to obtain spatially resolved plasma electron temperatures down to a few tens of eV and investigate various magnetohydrodynamic activities during a single-plasma discharge alone. Several applications including investigations of electron energy confinement during a period with central-cell electron cyclotron heatings are made with the novel position sensitive semiconductor arrays. [Copyright &y& Elsevier]

Elliptically shaped transition-region plasmas located between circularly shaped central cell and fish-tail shaped anchor-cell plasmas have been observed using X-ray tomography techniques for the first time in the world largest tandem mirror device, GAMMA 10. These three regions are connected through the lines of magnetic forces. Electrons are, therefore, anticipated to move easily through these regions along the magnetic field lines when neither appreciable electron losses into the transverse direction across the magnetic field lines nor the formation of electron transport barrier potentials in the parallel direction are expected. From this viewpoint, comparisons of electron temperature (Te) profiles in these regions, thus, give information on one of the most critical issues in tandem mirror plasma confinement. The first data on good agreement in Te profiles of the central cell and the transition region have supported this basic and essential concept of tandem mirror confinement. Development of position sensitive semiconductor-detector arrays and an upgraded X-ray tomography algorithm for analysing elliptically shaped transition-region plasmas are also reported. [Copyright &y& Elsevier]

A new method for a simultaneous observation of both plasma ion and electron temperatures is proposed using one semiconductor-detector array alone. This method will provide a new application of semiconductor-detector arrays for monitoring the key parameter set of nuclear-fusion triple product (i.e., ion temperatures, densities, and confinement time) as well as for clarifying physics mechanisms of energy transport between plasma ions and electrons under various plasma confining conditions. This method is developed on the basis of an alternative “positive” use of a semiconductor “dead layer”; that is, an SiO2 layer is employed as a reliable ultra-thin energy analysis filter for low-energy charge-exchanged neutral particles from plasmas ranging in ion temperatures from 0.1 to several tens of kilo-electron-volts. Using recent fabrication techniques for the thin and uniform SiO2 layers of the order of tens to hundreds of angstrom, our computer simulation and its experimental verification show the availability of such semiconductors for distinguishing neutral particles (for ion temperatures) from X-rays (for electron temperatures). These are simultaneously emitted from the plasmas into semiconductor detectors; however, we employ their quite different penetration lengths and the resultant different deposition depths and profiles in semiconductor materials. As a result, their output signals are distinguishable for these two different and fundamental species of plasmas. [Copyright &y& Elsevier]

The first results of simultaneous observations of temporally and spatially resolved electron temperatures (T[sub e]) in both circularly shaped central-cell and elliptically shaped anchor regions are reported in the GAMMA 10 tandem mirror. A data set is provided using a novel matrix-type x-ray semiconductor detector. The detector has seven “matrix columns” for the measurement of plasma x-ray profiles along with six “matrix rows” for simultaneous analyses of six different x-ray-energy ranges by the fabrication of six different thicknesses of SiO[sub 2] semiconductor surface layers from 1 to 495 nm as ultrathin and unbreakable “x-ray absorption filters.” Such a matrix idea enables us to analyze x-ray tomography data in the T[sub e] region down to a few tens of eV. Simultaneous application of the x-ray detectors in the central-cell and the anchor region gives information on not only detailed electron behavior in each region but also the mutually communicating relation between the two regions: The role of the anchor-region plasmas in magnetohydrodynamic plasma stabilization in the central-cell plasmas is confirmed by the data from these detailed simultaneous electron observations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In the GAMMA 10/PDX tandem mirror, plasma with strong ion-temperature anisotropy is produced by using the ion cyclotron range of frequency waves. This anisotropy of ion temperature causes several Alfvén-Ion-Cyclotron (AIC) waves to spontaneously excite in the frequency range just below the ion cyclotron frequency. In addition, difference-frequency (DF) waves are excited in the radial inner region of the plasma by wave–wave coupling among the AIC waves. The radial density profiles were measured at multi-axial positions using a frequency-modulation reflectometer with an axial array of microwave antennas, and an axial variation of the density was found to be significant. In addition, a relative phase difference of the DF wave between axially separated two points was first obtained by finely choosing the probing frequency of the reflectometers with a maximum coherence used as a measure, indicating that the DF wave is a propagating wave, while the pump AIC waves are standing waves in the axial region of measurement. [ABSTRACT FROM AUTHOR]

Characterizes the energy response of a semiconductor detector in the ASDEX Upgrade Tokamak for plasma x-ray tomography studies using synchrotron radiation from a positron storage ring at the National Institute for High Energy Physics in Japan. X-ray diagnostic systems in the tokamak; Uniformity of the detector response on various locations of the active area.

The multipass Thomson scattering (MPTS) technique is one of the most useful methods for measuring low-electron-density plasmas. The MPTS system increases Thomson scattering (TS) signal intensities by integrating all multipass (MP) signals and improving the TS time resolution by analyzing each pass signal. The fully coaxial MPTS system developed in GAMMA 10/potential-control and diverter–simulator experiments has a polarization-based configuration with image-relaying optics. The MPTS system can enhance Thomson scattered signals for improving the measurement accuracy and megahertz-order time resolution. In this study, we develop a new MPTS system comprising a laser amplification system to obtain continuous MP signals. The laser amplification system can improve degraded laser power and return an amplified laser to the MP system. We obtain continuous MP signals from the laser amplification system by improving the laser beam profile adjuster in gas scattering experiments. Moreover, we demonstrate that more MP signals and stronger amplified MP signals can be achieved via multiple laser injections to the laser amplification system in the developed MP system comprising a laser amplification system. [ABSTRACT FROM AUTHOR]

Our proposed “matrix-type” semiconductor detectors are applied for studying the local energy balance of bulk electrons in the tandem-mirror GAMMA 10. The matrix-type detector array consists of compactly produced six “rows” having different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channel units (“columns”) for measuring radiation profiles in the radial direction of plasmas. These various SiO2 layers are, thus, employed as “unbreakable ultrathin radiation-absorption filters” having various thicknesses to distinguish x rays from charge-exchange neutral particles and analyze the radial profiles of both plasma ion and electron temperatures simultaneously. The radial profiles of the energy confinement time and the thermal diffusivity obtained from the local energy balance analysis imply that the improvement of the plasma confinement is associated with the strong shear of radial electric fields due to a high plasma confining potentials. [ABSTRACT FROM AUTHOR]

Our proposed “matrix-type” semiconductor detectors are applied for studying the relaxation of ion anisotropic distribution functions having several keV in the central cell of the tandem mirror GAMMA 10. The matrix-type detector array consists of compactly produced six “rows” having different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channel units (“columns”) for measuring radiation profiles in the radial direction of plasmas. These various SiO2 layers are, thus, employed as “unbreakable ultrathin radiation–absorption filters” having various thicknesses to analyze x-ray energies and distinguish x rays from neutral particles simultaneously. Development of these detectors along with high power gyrotrons allow us to investigate energy transport analyses between ion-cyclotron heated hot ions and electron-cyclotron heated electrons. An application of the matrix-type detectors reveals detailed behavior of electron and ion relaxation from the perpendicular to parallel ion energies in the central cell. [ABSTRACT FROM AUTHOR]

An idea for using semiconductor detectors to simultaneously observe both plasma ion T[sub i] and electron T[sub e] temperatures is proposed. The idea is also experimentally verified in tandem-mirror plasma shots. This method is developed on the basis of an alternative "positive" use of a semiconductor "dead layer" as an energy-analysis filter. Filtering dependence of charge-exchange neutral particles from plasmas on the thickness of a thin (on the order of nm thick) SiO[sub 2] layer is employed for analyzing T[sub i] in the range from hundreds to thousands of eV. Even under the conditions of simultaneous incidence of such particles and x rays into semiconductor detectors, the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish particles (for T[sub i]) from x rays (for T[sub e]). In this letter, proof-of-principle plasma experiments for the proposed idea are carried out to verify the availability of this concept of distinguishing and identifying each value of T[sub i] and T[sub e] by the use of various thin filtering materials prior to the use of thinner dead layers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the design and fabrication of a new-type multilayer semiconductor x-ray detector for the purpose of the development of wide-energy-range-sensitive x-rays. Characterization of the multilayer detector; Application for a plasma-electron temperature detector.

Investigates the x-ray energy responses of silicon semiconductor detectors using synchronous radiation from a positron storage ring at the Photon Factory. Study of the fundamental physics mechanism of the output signals; Technique for obtaining the principles of the future designs of plasma x-ray detectors.

Characterizes the energy response of a new semiconductor-detector array in the DIII-D tokamak for plasma x-ray diagnostics using synchrotron radiation at the Photon Factor (KEK) in Japan. Clarification of good x-ray response; Variations in detector-channel responses.

A frequency multiplied microwave interferometer, a Hα line emission measurement system, and a high speed camera system were installed on the Pilot-PSI device for low frequency fluctuation study in the detached plasma condition. The two dimensional Hα line emission and its fluctuation were monitored with a fast visible camera with Hα filter. The coherent low frequency fluctuations of frequency of approximately 13 kHz were measured by all measurement systems. The stronger fluctuation intensities were observed in the downstream of the ionization front region in the detached plasma condition. Moreover, we show the clear difference between the strong fluctuation regions of the electron line density and Hα line emission for the first time. This means that the fluctuations of Hα line emissions was caused by not only electrons but also by hydrogen ions. [ABSTRACT FROM AUTHOR]

Presents a study which proposed an analytical method based on a theoretical model for the x-ray energy responses of silicon surface-barrier detectors (SSB). Description of the model used in the study; Formulas and calculated results supporting SSB calibration data; Discussion of results.

We have measured multipoint fluctuations inside a divertor simulation experimental module (D-module) during the transient discharge from attached to detached states in the tandem mirror device GAMMA 10/PDX. It was first observed that blob-/hole- like positive/negative spikes of the ion saturation current appeared non-periodically around the radially outer side edge on the V-shaped target plate. This tendency became outstanding in the transient state, and the typical speed and size of the isolated blob-like structures in the azimuthal direction were estimated. Additionally, lower-frequency periodic mode fluctuations and their changes due to plasma detachment were investigated not only in the D-module but also in the central cell with the microwave interferometer, etc. Odd and even modes continuously appeared during the discharge, in the range of several kilohertz. [ABSTRACT FROM AUTHOR]

A two-channel microwave reflectometer system with fast microwave antenna switching capability was developed and applied to the GAMMA 10 tandem mirror device to study high-frequency smallamplitude fluctuations in a hot mirror plasma. The fast switching of the antennas is controlled using PIN diode switches, which offers the significant advantage of reducing the number of high-cost microwave components and digitizers with high bandwidths and large memory that are required to measure the spatiotemporal behavior of the high-frequency fluctuations. The use of two channels rather than one adds the important function of a simultaneous two-point measurement in either the radial direction or the direction of the antenna array to measure the phase profile of the fluctuations along with the normal amplitude profile. The density fluctuations measured using this system clearly showed the high-frequency coherent fluctuations that are associated with Alfv'en-ion-cyclotron (AIC) waves in GAMMA 10. A correlation analysis applied to simultaneously measured density fluctuations showed that the phase component thatwas included in a reflected microwave provided both high coherence and a clear phase difference for the AIC waves, while the amplitude component showed neither significant coherence nor clear phase difference. The axial phase differences of the AIC waves measured inside the hot plasma confirmed the formation of a standing wave structure. The axial variation of the radial profiles was evaluated and a clear difference was found among the AIC waves for the first time, which would be a key to clarify the unknown boundary conditions of the AIC waves. [ABSTRACT FROM AUTHOR]

A shear Alfven wave at slightly below the ion-cyclotron frequency overcomes the ion-cyclotron damping and grows because of the strong anisotropy of the ion temperature in the magnetic mirror configuration, and is called the Alfven ion-cyclotron (AIC) wave. Density fluctuations caused by the AIC waves and the ion-cyclotron range of frequencies (ICRF) waves used for ion heating have been detected using a reflectometer in a wide radial region of the GAMMA 10 tandem mirror plasma. Various wave-wave couplings are clearly observed in the density fluctuations in the interior of the plasma, but these couplings are not so clear in the magnetic fluctuations at the plasma edge when measured using a pick-up coil. A radial dependence of the nonlinearity is found, particularly in waves with the difference frequencies of the AIC waves; bispectral analysis shows that such wave-wave coupling is significant near the core, but is not so evident at the periphery. In contrast, nonlinear coupling with the low-frequency background turbulence is quite distinct at the periphery. Nonlinear coupling associated with the AIC waves may play a significant role in the beta- and anisotropy-limits of a mirror-confined plasma through decay of the ICRF heating power and degradation of the plasma confinement by nonlinearly generated waves. [ABSTRACT FROM AUTHOR]

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]

A new antenna array is proposed in order to improve the sensitivity and complexity of microwave imaging diagnostics systems such as a microwave imaging reflectometry, a microwave imaging interferometer, and an electron cyclotron emission imaging. The antenna array consists of five elements: a horn antenna, a waveguide-to-microstrip line transition, a mixer, a local oscillation (LO) module, and an intermediate frequency amplifier. By using an LO module, the LO optics can be removed, and the supplied LO power to each element can be equalized. We report details of the antenna array and characteristics of a prototype antenna array. [ABSTRACT FROM AUTHOR]

We have developed an analysis method to improve the accuracies of electron temperature measurement by employing a fitting technique for the raw Thomson scattering (TS) signals. Least square fitting of the raw TS signals enabled reduction of the error in the electron temperature measurement. We applied the analysis method to a multi-pass (MP) TS system. Because the interval between the MPTS signals is very short, it is difficult to separately analyze each Thomson scattering signal intensity by using the raw signals. We used the fitting method to obtain the original TS scattering signals from the measured raw MPTS signals to obtain the electron temperatures in each pass. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

Plasmas with high ion temperature of several kiloelectronvolts and a strong temperature anisotropy of greater than 10 were produced by ion cyclotron range of frequency (ICRF) heating in the GAMMA 10 tandem mirror. In such high-performance plasmas with strong anisotropy, high-frequency fluctuations, so-called Alfven-ion-cyclotron (AIC) waves, are excited spontaneously. These AIC waves have several discrete peaks in the frequency spectrum. Coupling of the ICRF heating waves and the excited AIC waves was clearly observed in the density fluctuations measured with a newly developed reflectometer. Parametric decay from the heating ICRF waves to the AIC waves and low-frequency waves was also indicated. Alfven waves with difference frequencies between the discrete peaks of the AIC waves were detected in a signal that measured the number of axially transported high-energy ions (over 6keV) at the machine end, indicating pitch-angle scattering caused by the low-frequency waves. Energy transport along the magnetic field line is an important consideration when ICRF power is injected in the perpendicular direction to a magnetic field line. The importance of the spontaneously excited AIC waves for axial confinement of a tandem mirror through wave-wave couplings was demonstrated. [ABSTRACT FROM AUTHOR]

A correlation between drift-type fluctuations and anomalous radial transport was observed in GAMMA 10, and these fluctuations were suppressed by the electron-cyclotron-heating-driven radial electric field. We developed new diagnostics to conduct these studies: a simultaneous two-point-measurement gold neutral beam probe (GNBP) for the radial electric field and potential fluctuations, and a high-speed end-plate potential fluctuation measurement system. The electric field and its fluctuations were successfully obtained in a single plasma shot for the first time. Coherence between the drift-type potential fluctuations measured in the core plasma by the GNBP and those obtained by end- plate measurements was clearly observed. These potential and electric field fluctuations were clearly suppressed by the positive electric fields measured by two-point potential measurements using the GNBP and the end-plate system. We can obtain a powerful tool for probing the radial electric field and potential fluctuations in the core plasma because the end-plate potential fluctuation is the same as that in the core plasma measured using the new GNBP. [ABSTRACT FROM AUTHOR]

The controlled formation of an internal transport barrier (ITB) is observed in GAMMA 10 [T. Cho et al., Nucl. Fusion 45, 1650 (2005)]. The barrier is localized within a layer of a strongly sheared Er×B plasma rotation (5.5

Abstract: For the purpose of clarifying the spatial structures of plasma potentials and ion-current signals for plasma confinement studies in open-field plasma devices, multigridded electrostatic ion-energy spectrometers (IES) and compact-sized electrostatic ion-current detectors (ICD) are developed. These IES and ICD detectors are alternately placed in an array unit, and installed in the end region of the GAMMA 10. This position-sensitive ion-detector structure is proposed to obtain precise ion-energy spectra and absolute values of ion currents without any perturbations from simultaneously incident energetic electrons into the array. For employing this specific method, it is worth noting that no further additional magnetic systems except ambient open-ended magnetic fields are required for the proposed detector structure. This characteristic property provides a compactness of the total detector system and availability for its use in a plasma confinement device without disturbing plasma-confining magnetic fields. Availability of the detector is clearly demonstrated in the GAMMA10 plasma experiments. [Copyright &y& Elsevier]

The first experimental demonstration of simultaneous measurements of temporally and spatially resolved ion-confining potentials φc and end-loss-ion fluxes IELA has been carried out during a single plasma discharge alone by the use of newly designed ion-energy-spectrometer arrays installed in both end regions of the GAMMA 10 tandem mirror. This position-sensitive ion-detector structure is proposed to obtain precise ion-energy spectra without any perturbations from simultaneously incident energetic electrons into the arrays. The relation between φc and IELA is physically interpreted in terms of Pastukhov’s potential confinement theory. In particular, the importance of axisymmetric φc formation is found for the plasma confinement. [Copyright &y& Elsevier]