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A new tomographic scheme is proposed for reconstructing three dimensional (3D) impurity emission distributions from two dimensional (2D) measurements with a single field-of-view in the magnetized edge plasma in a Large Helical Device (LHD). The 2D image is obtained with a multi-channel fiber array spectrometer, which views the entire region of the edge stochastic magnetic layer of LHD, including divertor plates, divertor legs, the stochastic layer, and the last closed flux surface. The scheme introduces new regularization terms in the Lagrangian function, based on the transport feature in magnetized plasma that the transport parallel to the magnetic field lines is much faster than the transport across the magnetic field, thus assuming smooth distribution in the parallel direction. The scheme is benchmarked with the test data of 3D distribution in the measurement volume, where the effectiveness of the various regularization terms is surveyed and feasibility of the scheme is confirmed. The new scheme is applied to the experimental data in LHD for carbon impurity emissions of C1+ and C3+, where the obtained distributions are discussed taking into account the plasma wall interaction and charge dependence of ionization potentials., source:Review of Scientific Instruments 89, 123502 (2018), source:https://doi.org/10.1063/1.5048218, identifier:0000-0002-7368-8614

This paper presents carbon impurity flow velocity and temperature measurements in the divertor region for a wide density range ne = (1 - 14) × 1019 m−3, central electron temperature Te = 1.5 - 3.5 keV, and with total neutral beam injection power of 9 - 12 MW. The isotope effect on the transport is studied in hydrogen (H) and deuterium (D) discharges. Flow velocities for D plasma are systematically slower, by the factor of 1.4 - 2, compared to H plasma. For all selected discharges, the carbon ions flow toward the divertor in both H and D plasmas. Different velocities are obtained depending on the charge states. For C+ and C2+ they are in the range of 10 - 30 km/s, and 5 - 20 km/s for C3+ ions. It is also found that there is no change of flow direction even in the lowest density, where the impurity transport model predicts flow toward upstream in the thermal force dominant regime. In H discharges velocities increase proportionally to the plasma density, while in D discharges this dependency is weaker. Possible mechanism to interpret these observations is discussed based on the parallel momentum balance of impurity transport., source:https://doi.org/10.1585/pfr.13.3402058, identifier:0000-0002-8429-3298

Hydrogen plasma-driven permeation (PDP) experiments have been performed using a sputter-deposited tungsten (SP-W) coated F82H membrane in the spherical tokamak QUEST. It has been found that SP-W coatings tend to enhance hydrogen PDP compared with that of bare F82H membrane. Surface recombination is a key process determining the PDP flux, suggesting that surface effects on hydrogen PDP should be further investigated., source:https://doi.org/10.1585/pfr.12.1305038

In order to understand plasma transport in the edge stochastic layers, a visible spectrometer has been developed. Two-dimensional impurity emission intensity distributions in the edge stochastic layer of LHD, including divertor plate, divertor legs, X-point, and the last closed flux surface, have been measured. Carbon emission intensities and their distributions are found to be clearly different depending on the different magnetic field configuration and on the charge state. Effects of the edge magnetic field structure on these results are discussed., source:https://doi.org/10.1585/pfr.13.3402030, identifier:0000-0002-7368-8614

First wall particle flux measurements in the QUEST spherical tokamak have been conducted, using a permeation probe that employs a first wall candidate ferritic steel alloy F82H as the membrane and also SUS304 as a comparative reference membrane. Permeation measurements have been done during the conditioning steady-state discharges heated with 2.45 GHz and 8.2 GHz ECR. Diffusion and recombination coefficients measured in a laboratory-scale plasma device: VEHICLE-1 are used to interpret the results from the permeation probe measurements in QUEST. These permeation membranes have been analyzed with XPS to evaluate the effects of surface impurities., source:https://doi.org/10.1585/pfr.9.3405041, identifier:0000-0001-9773-8121

Impurity flow velocity measurements have been conducted for different magnetic field configurations in a wide plasma parameter range in the divertor leg region of LHD for understanding of the edge impurity transport. In all cases (densities, magnetic configurations, hydrogen (H) & deuterium (D) discharges), flows of several tens of km/s are observed. It is found that the flow in thick stochastic layer is faster than in thin stochastic layer configuration by a factor of 3. Different velocities of different charge states of carbon impurity are observed. The simulation with EMC3-EIRENE code shows similar trend as the experiments, but only qualitatively: faster flow in H compared to D discharges due to the mass effect, faster flow in the case of thick stochastic layer. However, synthetic spectra show discrepancy with experiments in the absolute Doppler shift, where the impurity velocity in the experiments is one order faster compared to the simulations., source:https://doi.org/10.1016/j.nme.2018.11.009, identifier:0000-0002-8429-3298

0000-0001-9773-8121, First wall particle flux measurements in the QUEST spherical tokamak have been conducted, using a permeation probe that employs a first wall candidate ferritic steel alloy F82H as the membrane and also SUS304 as a comparative reference membrane. Permeation measurements have been done during the conditioning steady-state discharges heated with 2.45 GHz and 8.2 GHz ECR. Diffusion and recombination coefficients measured in a laboratory-scale plasma device: VEHICLE-1 are used to interpret the results from the permeation probe measurements in QUEST. These permeation membranes have been analyzed with XPS to evaluate the effects of surface impurities.