Radial profiles of ion temperature and plasma flow are measured at the n͞m 1͞1 magnetic island produced by external perturbation coils in the Large Helical Device. The sheared poloidal flows and sheared radial electric field are observed at the boundaries of the magnetic island, because the poloidal flow vanishes inside the static magnetic island. When the width of the magnetic island becomes large, the flow along the magnetic flux surface inside the magnetic island appears around the O point in the direction which reduces the shear of the poloidal flow at the boundary of the magnetic island.

In the first four years of the LHD experiment, several encouraging results have emerged, the most significant of which is that MHD stability and good transport are compatible in the inward shifted axis configuration. The observed energy confinement at this optimal configuration is consistent with ISS95 scaling with an enhancement factor of 1.5. The confinement enhancement over the smaller heliotron devices is attributed to the high edge temperature. We find that the plasma with an average beta of 3% is stable in this configuration, even though the theoretical stability conditions of Mercier modes and pressure driven low-n modes are violated. In the low density discharges heated by NBI and ECR, internal transport barrier (ITB) and an associated high central temperature (>10 keV) are seen. The radial electric field measured in these discharges is positive (electron root) and expected to play a key role in the formation of the ITB. The positive electric field is also found to suppress the ion thermal diffusivity as predicted by neoclassical transport theory. The width of the externally imposed island is found to decrease when the plasma is collisionless with finite beta and increase when the plasma is collisional. The ICRF heating in LHD is successful and a high energy tail (up to 500 keV) has been detected for minority ion heating, demonstrating good confinement of the high energy particles. The magnetic field line structure unique to the heliotron edge configuration is confirmed by measuring the plasma density and temperature profiles on the divertor plate. A long pulse (2 min) discharge with an ICRF power of 0.4 MW has been demonstrated and the energy confinement characteristics are almost the same as those in short pulse discharges.

The structure of the radial electric field and heat transport at the magnetic island in the Large Helical Device is investigated by measuring the radial profile of poloidal flow with charge exchange spectroscopy. The convective poloidal flow inside the island is observed when the n/m=1/1 external perturbation field becomes large enough to increase the magnetic island width above a critical value (15-20% of minor radius) in LHD. This convective poloidal flow results in a non-flat space potential inside the magnetic island. The sign of the curvature of the space potential depends on the radial electric field at the boundary of the magnetic island. The heat transport inside the magnetic island is studied with a cold pulse propagation technique. The experimental results show the existence of the radial electric field shear at the boundary of the magnetic island and a reduction of heat transport inside the magnetic island

Bolometer diagnostics are installed on the Large Helical Device (LHD) to provide measurements of the total (broad spectrum) electromagnetic radiation emitted by the plasma. Three types of detectors are used: resistive metal film bolometers, absolute extreme ultraviolet photodiodes and infrared imaging video bolometers. Details of the installation in LHD are given for each type of detector. The detector calibration, data analysis and tomography techniques are described and compared and sample results are shown.

Time-and-space resolved comparison of plasma expansion velocities in high-power diodes with velvet cathodes J. Appl. Phys. 113, 043307 (2013) Development of a diffuse air-argon plasma source using a dielectric-barrier discharge at atmospheric pressure Appl. Phys. Lett. 102, 033503 (2013) Nonmonotonic radial distribution of excited atoms in a positive column of pulsed direct currect discharges in helium Appl. Phys. Lett. 102, 034104 (2013) Iterative Boltzmann plot method for temperature and pressure determination in a xenon high pressure discharge lamp J. Appl. Phys. 113, 043303 (2013) Additional information on Rev. Sci. Instrum. The infrared ͑IR͒ imaging video bolometer ͑IRVB͒ is an imaging bolometer which uses a large (9 cmϫ9 cm) thin ͑1 m͒ gold foil and an IR camera to provide images of radiation from the plasma. Calibration of the IRVB using a lamp has been performed to compensate for any nonuniformities in the foil's thickness and its thermal properties due to blackening of the foil with graphite to improve the IR emissivity. This calibration revealed close to expected values for the calibration coefficient proportional to the product of the thermal conductivity and the foil thickness in the central region of the foil, while these values were anomalously high near the foil edge. The calibration coefficient proportional to the thermal diffusivity is a factor of 2 smaller than the expected value at the center and drops further at the edge of the foil. Using a derived expression for the IRVB noise equivalent power, a sensitivity comparison shows the IRVB using current IR technologies to be ϳ200 times less sensitive than an equivalent conventional resistive bolometer operating under ideal conditions.