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In this study, we observe avalanche-like electron thermal transport in Heliotron J under plasma conditions that exhibit power degradation to the central electron cyclotron heating (ECH). The newly installed GHz sampling electron cyclotron emission diagnostic allows for the observation of the long-distance radial propagation of electron temperature fluctuations. We find that the electron temperature fluctuations are associated with avalanches, because the Te fluctuations (i) propagate from the core to the edge with a speed comparable to the diamagnetic drift velocity, (ii) exhibit a 1/f power-law scaling in the frequency spectrum and a Hurst exponent close to 1, and (iii) dominate in the ECH deposition location and spread to the edge as the heating power increases. Furthermore, the electron heat avalanches can spread to the scrape off layer region when they are enhanced, i.e., the Te fluctuations correlate with the Dα emission, which also has a frequency spectrum that scales with a 1/f power law. [ABSTRACT FROM AUTHOR]

A retroreflector array, composed of a cluster of small retroreflectors, is experimentally studied for application to a Michelson-type interferometer system in the fusion plasma experiment. Such a new-type reflector has the potential to be a vital and effective tool at a spatially limited location, such as on the vacuum chamber wall of plasma experimental devices. To investigate the effect of retroreflector array on the reflected beam properties, a tabletop experiment is performed with the retroreflector array composed of 4 mm corner-cube retroreflectors and with a 320-GHz (λ ∼ 0.937 mm) submillimeter wave source. An imaging camera is utilized to measure the submillimeter wave beam profile and is scanned perpendicularly to the beam propagation direction if necessary. The experimental result exhibits a diffraction effect on the reflected beam, resulting in the emergence of discrete peaks on the reflected beam profile, as predicted in the past numerical study; however, the most reflected beam power converges on the one reflected into the incident direction, resulting from a property as a retroreflector. Furthermore, the dependence of the reflected beam on the incident beam angle is characterized while fixing the detector position, and the retroreflection beam intensity is found to vary due to the diffraction effect. Such an undesired variation of beam intensity induced by the diffraction can be suppressed with a focusing lens placed in front of the detector in the practical application to an interferometer. [ABSTRACT FROM AUTHOR]

The Paα line (1875.13 nm) in the near-infrared (NIR) region was evaluated to apply Stark broadening of the line spectrum to the electron density measurement of the small-pellet ablation cloud in Heliotron J, a medium-sized helical-axis heliotron device. Paα is three-to-four times broader than the visible Hβ line (486.13 nm) for the same electron density. Using a portable NIR spectrometer, preliminary proof-of-concept experiments determined the marginal density, below which the broadening was undetectable. The lower detection density limit can be decreased using a narrower entrance slit or a denser grating. [ABSTRACT FROM AUTHOR]

A new 320 GHz solid-state source interferometer is installed in the Heliotron J helical device to explore the physics of high-density plasmas (ne > 2–3 × 1019 m−3, typically) realized with advanced fueling techniques. This interferometry system is of the Michelson type and is based on the heterodyne principle, with two independent solid-state sources that can deliver an output power of up to 50 mW. A high time resolution measurement of <1 µs can be derived by tuning the frequency of one source in the frequency range of 312–324 GHz on the new system, which can realize the fluctuation measurement. We successfully measured the line-averaged electron density in high-density plasma experiments. The measured density agreed well with a microwave interferometer measurement using a different viewing chord, demonstrating that the new system can be used for routine diagnostics of electron density in Heliotron J. [ABSTRACT FROM AUTHOR]

Understanding pellet ablation physics is crucial to realizing efficient fueling into a high temperature plasma for the steady state operation of ITER and future fusion reactors. Here we report the first observation of the formation of fluctuation structures in the pellet plasmoid during the pellet ablation process by a fast camera in a medium-sized fusion device, Heliotron J. The fluctuation has a normalized fluctuation level of ~ 15% and propagates around the moving pellet across the magnetic field. By comparing the fluctuation structures with the shape of magnetic field lines calculated with the field line tracing code, we successfully reconstruct the spatio-temporal structure of the fluctuations during the pellet ablation process. The fluctuations are located at the locations displaced toroidally from the pellet and propagate in the cross-field direction around the pellet axis along the field line, indicating a three-dimensional behavior and structure of fluctuations. The fluctuation would be driven by a strong inhomogeneity formed around the pellet and invoke the relaxation of the gradient through a cross-field transport induced by the fluctuations, which could affect the pellet ablation and pellet fueling processes. Such fluctuations can be ubiquitously present at the inhomogeneity formed around a pellet in the pellet ablation process in fusion devices. [ABSTRACT FROM AUTHOR]

The hydrogen/deuterium (H/D) isotope effect on a zonal flow and its configuration dependence are experimentally studied in a helical device, Heliotron J. The isotope dependence of a toroidally symmetric potential fluctuation in the frequency range of <∼4 kHz, a zonal flow, is observed in low-density electron cyclotron resonance heated plasmas in Heliotron J. In the standard configuration, the zonal flow interacting with turbulence is enhanced as the D gas fraction increases. The zonal flow is more dominated against turbulent fluctuation in D plasmas, which should have a favourable impact on turbulence transport. Interestingly, however, the opposite dependence of the zonal flow activity on the isotope ratio is also observed in the different magnetic configurations. The configuration dependence observed in this experiment could be one of the factors to explain the difference in the isotope effect of confinement improvement between tokamaks and helical devices. Impurities and radial electric field, which can also be influenced by isotope mass through the difference in neoclassical transport and plasma-wall interaction, have insignificant influences on the zonal flow behaviour in this experiment. [ABSTRACT FROM AUTHOR]

The sensitivity of an infrared imaging video bolometer (IRVB) was improved for the measurement of relatively low energy plasma radiation from the viewpoint of the metal foil absorber material. The photon energy of the radiation was considered up to 1 keV for the divertor plasma measurement. The thickness of the foil absorber was evaluated not only for conventional heavy elements, e.g., platinum, but also for light elements by the relation between the photon energy and attenuation length and by mechanical strength. A heat-transfer calculation using ANSYS suggested that light elements with practical foil thickness provide a higher temperature rise of the foil absorber compared with heavier elements with practical foil thickness. The maximum of the temperature rise was evaluated using He–Ne laser irradiation onto absorber samples. The material dependence of the temperature rise has a similar tendency between calculations and experiments. Experimentally, the sensitivity of the IRVB improved from 280 to 110 µW/cm2 using titanium with 1 µm thickness compared with conventional platinum with 2.5 µm thickness. Consequently, the signal-to-noise ratio of the IRVB could be improved from 2.8 to 9.1. [ABSTRACT FROM AUTHOR]

This study shows the feasibility of a beam emission spectroscopy (BES) diagnostic in the Helically Symmetric eXperiment (HSX) stellarator for obtaining the spatiotemporal structure of density fluctuation. A beam emission simulation was applied to HSX plasmas to design and optimize viewing chords and to estimate the beam emission spectrum. A Doppler-shifted beam emission spectrum was measured from a 30 kV, 4 A diagnostic neutral beam injected into HSX plasmas. The beam emission was measured with a high-time-resolution avalanche photodiode (APD) assembly to determine the feasibility of BES in HSX. For HSX plasmas heated by 28 GHz electron cyclotron heating, a mode around f = 15 kHz was observed in the BES signal. The coherence between the BES signal and the density fluctuation measured by an interferometer system was significant. A plan for improving the BES system to enable the measurement of higher frequency related to turbulent transport is presented. The array of sightlines proposed in this study can be used to measure beam emission with a Doppler shift larger than 3 nm (blue shift), which enables the use of a wide passband interference filter to obtain higher throughput. The adoption of a large objective optics and a chilled APD assembly will improve the signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

We report the development of a new interferometer with two stable, high-power, 320 GHz solid-state sources in Heliotron J. A heterodyne Michelson interferometer optical scheme is employed. Two solid-state oscillators are utilized as sources with a fixed frequency at 320 GHz and frequency tunable of 312–324 GHz. Quasi-optical techniques are used for beam transmission. The beam is elongated in the vertical direction with two off-axis parabolic mirrors and injected into the plasma as a sheet beam for the multi-channel measurement (>5 ch.). Passing through the plasma, the beam is reflected at a retroreflector-array installed at the vacuum chamber wall. The retroreflector-array is a bunch of retroreflector structures, which can suppress the beam refraction caused by plasma without much space inside a vacuum chamber unlike a single retroreflector and can facilitate the system design. The source, detectors, and the retroreflector-array are tested to evaluate their basic performance on a tabletop experiment. [ABSTRACT FROM AUTHOR]

In this article, we report the latest results for the impacts of the isotope mass and the plasma heating scenario on the spatiotemporal characteristics of the low-frequency zonal flow (ZF)-like electrostatic oscillation found in the plasma edge of the TJ-II stellarator. The radial profile of the toroidal cross-coherence in low-frequency floating potential fluctuations (1 < f < 25 kHz), known as long-range correlations (LRCs), was explored along the plasma boundary region by a dual Langmuir probe system. The study was performed using electron cyclotron resonance heating (ECRH)- and neutral beam injection (NBI)-heated plasmas with two different isotope concentrations: pure hydrogen plasmas and plasmas dominated by deuterium (). The highest toroidal coherence levels are detected for floating potential oscillations at less than 10 kHz in hydrogen and deuterium plasmas, in both the ECRH and NBI heating schemes. The radial extent of the LRC profile is clearly larger in the ECRH than in the NBI-heated plasma scenarios. While the maximum amplitude of the LRC does not show a significant dependence on isotope mass, the relation between the LRCs' radial sizes in plasmas and different isotope masses increases with the isotope mass in NBI-heated scenarios. These results provide the first experimental observation of ZFs with a larger radial size in deuterium than in hydrogen plasmas. [ABSTRACT FROM AUTHOR]

A real-time interlock system for power injection in electron cyclotron resonance heating (ECRH) was developed to be applied to Large Helical Device (LHD) plasma. This system enabled perpendicular injection, thus improving the performance of ECRH more than has ever been achieved before in LHD. Perpendicular propagation of the electron cyclotron wave at 77 GHz became more insensitive to the effect of refraction in comparison to the conventional oblique propagation. The achieved central electron temperature in the case of perpendicular injection was approximately 2 keV higher than that in the case of standard oblique injection for a central electron density of 1 × 1019 m−3 by 1 MW injection. With such improved performance of ECRH, high-density ECRH plasma of 8 × 1019 m−3 was successfully sustained after the injection of multiple hydrogen ice pellets for the first time in LHD. [ABSTRACT FROM AUTHOR]

A phase tracking method based on Hilbert transform algorithm is applied to the nonlinear wave-wave coupling analysis on HL-2A tokamak. Synthetic signal analysis is given to show the principle of phase analysis for the detection of nonlinear coupling. If the phase difference between two coherent modes is synchronized with the phase of a third mode, these three modes are nonlinearly coupled, vice versa. The time evolution of the phase of a coherent mode could be computed with Hilbert transform for experimental data, and a phase tracking flowchart is summarized. On HL-2A tokamak, the nonlinear coupling among two Alfvén modes (AMs) and a tearing mode (TM) has been confirmed with bicoherence analysis (Shi et al 2017 Phys. Plasmas 24 042509). With Hilbert transform, it is clearly observed that the phase difference between two AMs Δθ12 is synchronized with the phase of the TM θTM. The synchronization is confirmed with normalized cross-correlation. An alternative to check this synchronization is to observe the histogram of the phase difference Δθ12 − θTM. [ABSTRACT FROM AUTHOR]

Alfvén eigenmodes destabilized by energetic particles in Heliotron J, a low magnetic shear helical axis stellarator/heliotron with four toroidal equilibrium field periods, are investigated with MEGA, a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic fluid. The objectives of this study are to validate the MEGA simulation results on Alfvén eigenmodes in Heliotron J, and to clarify the properties of Alfvén eigenmodes. The experimentally observed global Alfvén eigenmode (GAE) was reproduced with MEGA simulations based on the experimental bulk plasma temperature and density profiles. Beside GAE, GAE was also observed with lower amplitude and linear growth rate. The frequency and spatial location of GAE are close to those of the experimentally observed energetic particle mode (EPM). For GAE, it was found that the three-dimensional spatial profile of the GAE was primarily composed of n = 2 harmonics while the contribution from the other toroidal mode numbers such as n = 2 ± iNfp was weak, where 'i' and 'Nfp' are arbitrary integer and toroidal field period, respectively. This indicates that the coupling of harmonics with the same toroidal mode number through toroidicity is dominant for the GAE spatial profile, and the coupling with the different toroidal mode numbers through helicity and bumpiness has minor effects. For GAE, the coupling of harmonic through toroidicity is weaker than that of GAE. The non-linear evolutions of the GAE and GAE destabilized by energetic particles with a bump-on-tail distribution and a slowing-down distribution were compared. Weak dependence of the linear growth rate for both and modes on charge-exchange time were implied. [ABSTRACT FROM AUTHOR]

Here, we report on a study of seed plasmas produced by non-resonant 2.45 GHz microwave heating in Heliotron J, which is useful for plasma start-up by neutral beam injection (NBI) under the conditions of low beam power (<1 MW), low accerelation voltage (<30 kV) and small device size (∼1 m). The pre-ionization technique using the non-resonant heating produced the electron density in the order of 1017–1018 m−3 with the energy exceeds the CII ionization potential (30 eV). The existence of the relativistic electrons, which was essential to produce the seed plasmas, was confirmed experimentally during the pre-ionization phase by the synchrotron radiation and the hard x-ray emission measurements. The production mechanism of the relativistic electrons was considered to be stochastic interactions between the electrons and the microwave-frequency field. By optimizing the additional gas fueling during the microwave launch, a higher seed-plasma density more than 4 × 1018 m−3 was obtained, resulting that a rapid density evolution after NBI turn-on was successful even in the low NBI power (0.3 MW) condition. The seed plasmas produced by the pre-ionization method is useful to realize the plasma start-up under low absorption power condition in larger heliotron/stellarator devices such as perpendicular NBI in W7-X or deuterium NBI in LHD. [ABSTRACT FROM AUTHOR]

When realising future fusion reactors, their stationary burning must be maintained and the heat flux to the divertor must be reduced. This essentially requires a stationary internal transport barrier (ITB) plasma with a fast control system. However, the time scale for determining the position of the foot point of an ITB is not clearly understood even though its understanding is indispensable for fast profile control. In this study, the foot point of the electron ITB (eITB) was observed to be reformed at the vicinity of a magnetic island when the island started to form. In addition, the enhanced confinement region was observed to expand during the eITB formation according to the radial movement of the magnetic island toward the outer region. Compared to the time scales of the local heat transport, the faster time scales of the movement of the eITB foot point immediately after island formation (~0.5 ms) suggest the importance of the magnetic island for plasma profile control to maintain stationary burning. [ABSTRACT FROM AUTHOR]

We report an electrical characterization of nanographite fibers (NGFs) by measuring current–voltage characteristics of the individual NGFs in air at room temperature in order to optimize the NGF mass production process. The NGFs were synthesized by thermal chemical vapor deposition with thermal annealing. The NGF contains many defects in comparison with a multiwalled carbon nanotube (MWNT) synthesized by arc discharge, which can be clearly confirmed in the current–voltage characteristic. The maximum current density, however, is typically 10[sup 8] A/cm[sup 2], which is comparable to that in the MWNT. The high-density current operation mechanism is inferred from the measured diameter dependence of the current-voltage characteristic in various diameter NGFs. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Metal–oxide–semiconductor structures with a Ge nanocrystal embedded in SiO[sub 2] films were fabricated by Ge[sup +] ion implantation and subsequent high-temperature annealing. The Raman spectra indicate the evidence of self-assembled Ge nanocrystals in the SiO[sub 2] films. The Ge size and its density were estimated to 3–5 nm and 1×10[sup 12]/cm[sup 2], respectively. Photoluminescence spectra showed a strong blue–violet band around 400 nm and a weak near-infrared band around 750 nm, respectively. The several implantation-induced deficient centers are believed to be responsible for the blue-light luminescence. Capacitance–voltage characteristics exhibit the flatband voltage shifts of 1.02 V after the electron injection into the SiO[sub 2]/Ge/SiO[sub 2] potential well. An anomalous leakage current was clearly observed in the current–voltage characteristics. The precise simulation of quantum electron transport in the SiO[sub 2] film indicates that the anomalous conduction is originated from resonant tunneling in the SiO[sub 2]/Ge/SiO[sub 2] double-well band structure. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A possibility of electron density measurements with heavy ion beam probes (HIBPs) has been demonstrated, along with their capability to measure the potential and magnetic field. A method has been proposed to reconstruct the electron density profile [A. Fujisawa et al., Rev. Sci. Instrum. 74, 3335 (2003)]. In the method, the profile of secondary beam currents is converted into a local density profile by taking into account local brightness and so-called path integral effects which mean the effect of beam attenuation along the beam orbit. Here the article presents the HIBP measurement of the electron density profile after the proposed method was first applied on the real experimental data of compact helical system plasmas. In the real application, the hollow density and the peaked profiles are successfully obtained with sufficiently high temporal resolution (a few ms), in accordance with the electron density profile measured with Thomson scattering for electron cyclotron resonance heating and neutral beam injection plasmas. [ABSTRACT FROM AUTHOR]

Presents a study which tested metal insulator metal junctions fabricated on a glass substrate as hydrogen sensors. Measurement of the current versus voltage characteristics of the junctions at room temperature; Experimental procedure; Results and discussion.

Presents a study which produced a superconducting niobium nitrate from carbon fibers and sapphire substrates by direct current reactive magnetron sputtering. Experiment; Results and discussion; Conclusions.

An injection barrel was designed and fabricated for a small size 0.8 mm cryogenic pellet with a low speed of 200-300 m/s in medium-sized plasma fusion devices. Pellet injection with pneumatic acceleration was examined using a conventional in situ technique. A tapered structure was applied in the downstream side of the injection barrel to satisfy the requirement of pellet speed reduction by expansion of the propellant gas. Shadowgraph and light gate measurements show that the intact pellets have speeds of 260 ± 30 m/s and a typical size of 1.1-1.2 mm. The pellet ablation code based on a neutral gas shielding model shows that the penetration depth of the measured pellet parameters does not cross the plasma center, even in medium-sized plasma devices such as the Heliotron J helical device. The injection barrel with a tapered structure developed in this study is feasible for low speed pellet injection. [ABSTRACT FROM AUTHOR]

In this study, we developed a new frequency-tuning method for 700-MHz nuclear magnetic resonance (NMR) pickup coils. We determined an optimal Helmholtz-type one-turn coil, by using an electromagnetic simulator, and fabricated a pickup coil using \textYBa2\text{Cu}3\text{O}7-\delta (YBCO) thin films. We examined the resonance frequency shift of the pickup coils obtained with a sapphire plate by using a 3-D electromagnetic-field simulator and obtained a 31.5-MHz shift. We also examined the frequency shift obtained using a quasi-NMR pickup coil system and found that it was 29.3 MHz. This value is sufficient for the frequency tuning in an actual NMR system. It became clear that resonance frequency tuning using a sapphire plate was possible. [ABSTRACT FROM PUBLISHER]

A moment approach to calculate neoclassical transport in non-axisymmetric torus plasmas composed of multiple ion species is extended to include the external parallel momentum sources due to unbalanced tangential neutral beam injections (NBIs). The momentum sources that are included in the parallel momentum balance are calculated from the collision operators of background particles with fast ions. This method is applied for the clarification of the physical mechanism of the neoclassical parallel ion flows and the multi-ion species effect on them in Heliotron J NBI plasmas. It is found that parallel ion flow can be determined by the balance between the parallel viscosity and the external momentum source in the region where the external source is much larger than the thermodynamic force driven source in the collisional plasmas. This is because the friction between C6+ and D+ prevents a large difference between C6+ and D+ flow velocities in such plasmas. The C6+ flow velocities, which are measured by the charge exchange recombination spectroscopy system, are numerically evaluated with this method. It is shown that the experimentally measured C6+ impurity flow velocities do not contradict clearly with the neoclassical estimations, and the dependence of parallel flow velocities on the magnetic field ripples is consistent in both results. [ABSTRACT FROM AUTHOR]

Objective: Interferon alpha (IFN-α) is a key cytokine associated with systemic lupus erythematosus (SLE). IFN-α induces the expression of CD64 on monocytes (mCD64). Although enhanced mCD64 expression has been reported in patients with SLE, it has never been assessed quantitatively. The aim of this study was to investigate whether or not mCD64 expression correlates with SLE disease activity. Methods: The mCD64 expression levels were assessed quantitatively in 40 patients with active or inactive SLE by using flow cytometry. The mCD64 expression levels were subsequently compared with the SLE disease activity index (SLEDAI) and levels of existing SLE activity biomarkers, such as anti-DNA antibody, complements, and so on. Results: The mCD64 expression was significantly higher in active disease than in inactive disease SLE (median molecules/cell, interquartile range: 34,648, 8174–24,932 and 20,865, 6357–21,503, respectively; p < 0.001). The levels of mCD64 expression strongly correlated with SLEDAI (r = 0.68, p < 0.001). Conclusion: The mCD64 expression is a simple and useful biomarker for evaluating disease activity in patients with SLE. [ABSTRACT FROM AUTHOR]

We propose a Helmholtz-type probe coil that uses a high-temperature superconductor (HTS) for use as 700-MHz nuclear magnetic resonance (NMR) RF coils with a high unloaded quality factor (Qu). We analyzed the microwave resonant properties of a one-turn coil set face-to-face. The coils were made of a \YBa2\Cu3\O7-\delta (YBCO) film deposited on an r-plane sapphire substrate. The film thickness was 300 nm. The resonant frequency was found to split into in-phase (lower frequency) and out-phase (higher frequency) modes. We focused on the self-resonant frequency of the one-turn coil. We simulated the horizontal magnetic field caused by the RF coil. Although the coil could generate a sufficiently large transverse magnetic field in the in-phase mode, such a large field could not be generated in the out-phase mode. Therefore, we decided to use the in-phase mode. We also measured and simulated Qu to confirm that it was large enough for use in the 700-MHz NMR system. [ABSTRACT FROM PUBLISHER]

Microminipigs are extremely small-sized, novel miniature pigs that were recently developed for medical research. The inbred Microminipigs with defined swine leukocyte antigen ( SLA) haplotypes are expected to be useful for allo- and xenotransplantation studies and also for association analyses between SLA haplotypes and immunological traits. To establish SLA-defined Microminipig lines, we characterized the polymorphic SLA alleles for three class I ( SLA-1, SLA-2 and SLA-3) and two class II ( SLA- DRB1 and SLA- DQB1) genes of 14 parental Microminipigs using a high-resolution nucleotide sequence-based typing method. Eleven class I and II haplotypes, including three recombinant haplotypes, were found in the offspring of the parental Microminipigs. Two class I and class II haplotypes, Hp-31.0 ( SLA-1*1502- SLA-3*070102- SLA-2*1601) and Hp-0.37 ( SLA- DRB1*0701- SLA- DQB1*0502), are novel and have not so far been reported in other pig breeds. Crossover regions were defined by the analysis of 22 microsatellite markers within the SLA class III region of three recombinant haplotypes. The SLA allele and haplotype information of Microminipigs in this study will be useful to establish SLA homozygous lines including three recombinants for transplantation and immunological studies. [ABSTRACT FROM AUTHOR]

A fluctuation analysis technique using analytic signals is proposed. Analytic signals are suitable to characterize a single mode with time-dependent amplitude and frequency, such as an MHD mode observed in fusion plasmas since the technique can evaluate amplitude and frequency at a specific moment without limitations of temporal and frequency resolutions, which is problematic in Fourier-based analyses. Moreover, a concept of instantaneous phase difference is newly introduced, and error of the evaluated phase difference and its error reduction techniques using conditional/ensemble averaging are discussed. These techniques are applied to experimental data of the beam emission spectroscopic measurement in the Heliotron J device, which demonstrates that the technique can describe nonlinear evolution of MHD instabilities. This technique is widely applicable to other diagnostics having necessity to evaluate phase difference. [ABSTRACT FROM AUTHOR]

This paper describes the development study of the beam emission spectroscopy (BES) for the turbulent transport study in Heliotron J. Modification of the sightlines (10 × 4 for edge and 10 × 2 for edge) enables us to obtain 2-dimensional BES imaging. The cooling effect on the reduction in the electrical noise of avalanche photodiode (APD) assembly has been investigated using a refrigerant cooling system. When the temperature of the APD element has set to be -20 °C, the electrical noise can be reduced more than 50%. The measurement error of the phase difference in the case of low signal level has been tested by two light-emitting diode lamps. The APD cooling has an effect to improve the measurement error at the low signal level of APD. [ABSTRACT FROM AUTHOR]

A Faraday-cup type lost-fast ion probe (FLIP) has been designed and installed in Heliotron J for the purpose of the studies of interaction between fast ions and MHD instabilities. The FLIP can measure the co-going fast ions whose energy is in the range of 1.7-42.5 keV (proton) and pitch angle of 90°-140°, especially for fast ions having the injection energy of neutral beam injection (NBI). The FLIP successfully measured the re-entering passing ions and trapped lost-fast ions caused by fast-ion-driven energetic particle modes in NBI heated plasmas. [ABSTRACT FROM AUTHOR]

A novel reconstruction method is developed for acquiring the electron density profile from multichannel interferometric measurements of strongly asymmetrical toroidal plasmas. It is based on a regularization technique, and a generalized cross-validation function is used to optimize the regular-ization parameter with the aid of singular value decomposition. The feasibility of method could be testified by simulated measurements based on a magnetic configuration of the flexible helical-axis heliotron device, Heliotron J, which has an asymmetrical poloidal cross section. And the successful reconstruction makes possible to construct a multi-channel Far-infrared laser interferometry on this device. The advantages of this method are demonstrated by comparison with a conventional method. The factors which may affect the accuracy of the results are investigated, and an error analysis is carried out. Based on the obtained results, the proposed method is highly promising for accurately reconstructing the electron density in the asymmetrical toroidal plasma. [ABSTRACT FROM AUTHOR]

Edge fluctuation in a supersonic molecular-beam injection (SMBI) fueled plasma has been measured using an electrostatic probe array. After SMBI, the plasma stored energy (Wp) temporarily decreased then started to increase. The local plasma fluctuation and fluctuation induced particle transport before and after SMBI have been analyzed. In a short duration (4 ms) just after SMBI, the density fluctuation of broad-band low frequency increased, and the probability density function (PDF) changed from a nearly Gaussian to a positively skewed non-Gaussian one. This suggests that intermittent structures were produced due to SMBI. Also the fluctuation induced particle transport was greatly enhanced during this short duration. About 4ms after SMBI, the low frequency broad-band density fluctuation decreased, and the PDF returned to a nearly Gaussian shape. Also the fluctuation induced particle transport was reduced. Compared with conventional gas puff, Wp degradation window is very short due to the short injection period of SMBI. After this short degradation window, fluctuation induced particle transport was reduced and Wp started the climbing phase. Therefore, the short period of the influence to the edge fluctuation might be an advantage of this novel fueling technique. On the other hand, although their roles are not identified at present, coherent MHD modes are also suppressed as well by the application of SMBI. These MHD modes are thought to be de-exited due to a sudden change of the edge density and/or excitation conditions. [ABSTRACT FROM AUTHOR]

Second harmonic electron cyclotron current drive (ECCD) has been applied in the stellarator/heliotron (S/H) device, Heliotron J, to stabilize magnetohydrodynamic (MHD) modes. The energetic particle mode (EPM) of 60–90 kHz frequency, one of the energetic-ion-driven MHD modes, is excited in a plasma heated by co- and counter-neutral beam injection and electron cyclotron heating (ECH). The EPM has been stabilized by counter-ECCD which decreases the rotational transform. Localized EC current driven by a few kA at the central region modifies the rotational transform profile, ι/2π, leading to the formation of a high magnetic shear at the radius where the mode is excited. An experiment scanning the EC-driven current shows that there is a threshold in magnetic shear and/or rotational transform to stabilize the EPM. [ABSTRACT FROM AUTHOR]

Alfvén eigenmode (AE) activity driven by NBI-produced fast ions is observed in TJ-II plasmas. A two-step response of the measured AEs to electron cyclotron heating (ECH) power is seen. In a first step, the continuous character of the unstable AEs changes to a chirping character of the marginally unstable AEs when moderate values of ECH power are applied to the NBI-only-heated plasma. In a second step, a significant reduction of the AE amplitude is observed when the ECH power is doubled. This stabilizing effect has been experimentally confirmed both on a shot-by-shot basis and along a single discharge by means of ECH modulation. The observed stabilizing effect is stronger with on-axis ECH than with off-axis ECH power injection. [ABSTRACT FROM AUTHOR]

X-ray line spectra ranging from 17 to 77 keV were quantitatively measured with a Laue spectrometer, composed of a cylindrically curved crystal and a detector. Either a visible CCD detector coupled with a CsI phosphor screen or an imaging plate can be chosen, depending on the signal intensities and exposure times. The absolute sensitivity of the spectrometer system was calibrated using pre-characterized laser-produced x-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an open code for x-ray diffraction. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer agency for specific x-ray line emissions, is derived as a consequence of this work. [ABSTRACT FROM AUTHOR]