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Thermal probe with double function of thermocouples and Langmuir probe has been developed, and the initial data observed in far-SOL in QUEST is obtained. Heat flux of megawatt per square meters related to energetic electrons and sonic plasma flow in far-SOL have been observed in the current rump-up phase although no high power inductive force like ohmic winding is applied. The heat flux and the flow are suppressed after the current is built up. In the quasi-steady state, plasma current starts and keeps sawtooth-like oscillation with 20 Hz frequency. The heat flux and the flow in far-SOL have clear responses to the oscillation.

Global particle balance in non-inductive long-duration plasma on QUEST has been investigated. Approximately 70% of the fuel hydrogen (H) was retained in the wall and then was almost exhausted just after the discharge. The global recycling ratio (Rg), defined as the ratio of the evacuated H2 flux to that injected, was found to gradually increase during discharges and subsequently rose rapidly. To study the growth of Rg, the thermal desorption spectra after deuterium implantation in a specimen exposed to QUEST plasma was analyzed with a model which includes reflection, diffusion, solution, recombination, trapping, and plasma-induced desorption in the re-deposition layer. The model reconstructs the growth of Rg during a long-duration plasma and indicates solution plays a dominant role in the growth.

In order to investigate the overall atomic hydrogen background and the dynamic characteristics of wall pumping/fuelling phenomenon, a permeation probe system has been developed and applied in the spherical tokamak QUEST. Reliability of measurements, within ±3% accuracy and a positive correlation with the hydrogen line emission over three orders of magnitude have been demonstrated for more than 3000 various plasma discharges. By comparison of the experimental permeation (flux) curves with the numerically simulated curves, the net incident atomic hydrogen flux is evaluated in the range of 1 × 1019 H m−2 s−1 to 4 × 1020 H m−2 s−1. The atomic flux has been investigated as a function of various plasma operation parameters like RF power, gas pressure and magnetic configuration. Using the static particle balance and permeation measurements, the progress in wall conditioning has been investigated. An inverse correlation between the atomic hydrogen flux and improvement in wall pumping has been observed over the two campaigns.

The JT-60SA divertor has to withstand a maximum heat flux of ∼15 MW/m2 for 100 s, and JAEA has developed the monoblock-type CFC divertor target for JT-60SA. To boost production yield of the targets, CFC cracking due to thermal expansion and contraction of the CuCrZr cooling tubes must be suppressed. CuCrZr properties depend strongly on the heat treatment, and the target is heat-treated during the manufacturing processes of brazing, solution treatment, and annealing. CuCrZr test specimens were heat-treated with the targets, and the strength and hardness of the specimens were almost the same for the quenching cooling rates of ∼0.65 °C/s and ∼1.5 °C/s around 800 °C. This indicates that the slower quenching cooling rate is acceptable, and consequently at least half of the mock-ups could remove the required high heat flux of 15 MW/m2.

Metallic dust behavior was observed in full lower hybrid current drive plasmas on TRIAM-1M, which had all-metal plasma facing components. TRIAM-1M was shut-down on December 2005 and then in-vessel dusts were collected with a suction aspirator through a membrane filter of 100 nm meshes. The toroidal distribution of the total mass of collected in-vessel dusts was measured and the largest amount was found to be near the vertical movable limiter (VML). The typical size of in-vessel dusts was 1–10 μm and the impact on augmenting the surface area was not significant. Dusts were observed to be either flaky or spherical in form and the majority of the flakes had accumulated around the VML. Eruption detritus were observed on the surface of large flakes and this suggests that the burst of blistering are one of the origins of in-vessel dusts.

Blob-like structures are observed in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. The combined measurement with a fast camera and a movable Langmuir probe show that visible filamentary structures extended along field lines do correspond to over-dense plasma structures. Ion saturation current time trace shows a front-like asymmetric burst when a visible structure reaches the probe during its outward propagation. The typical radial velocity of the blob-like structure, V b , was measured as ∼1 km/s with the fast camera at the intermediate area. V b increased as the blob-like structure moved along major radius, R (outward). The average velocity of E × B drift derived from the probe measurement, slightly larger than V b , was also increased as the blob-like structure propagated to larger R .

Modification of JT-60 to a fully superconducting coil tokamak (JT-60 Super Advanced) has been started last year. Divertor plasma performance for high triangularity and low aspect ratio plasma in two types of divertor geometries was studied and compared by using 2D plasma fluid (SOLDOR) and neutral Monte-Carlo (NEUT2D) codes. ‘Vertical target with deep V corner’ is effective to reduce heat flux even in low density operation without additional gas puffing, but large pumping speed is required to change particle balance. On the other hand, the particle balance in ‘W-shaped with shallow V’ can be changed with small pumping speed and larger main plasma can be obtained due to its compactness. Performance of water-cooled mono-block carbon fiber composite (CFC) divertor target has been confirmed by heat load cycle test of small mockup. Obvious performance degradation was not found during 1450 cycles at 15 MW m−2 and 600 cycles at 20 MW m−2.

Laser welded V–4Cr–4Ti–0.15Y alloy, fabricated by National Institute for Fusion Science (NIFS), was used in this study. Copper ion irradiation was carried out with the tandem accelerator at Kyushu University. The TEM samples were sliced from the welded materials and irradiated at 873 K up to the dose of 12 dpa. The microstructure before the irradiation showed that relatively large precipitates, which were commonly observed in the alloy, disappeared in the center of the weld metal. After the ion irradiation, fine titanium oxides with {1 0 0} habit planes were detected. However, in all irradiation doses, the growth of titanium oxides was suppressed by Y addition.

An in situ and real time measurement system of erosion and deposition has been developed, which is based on interference of light on a thin semi-transparent layer of redeposited material on substrate. It has been applied to long duration discharges in TRIAM-1M. The sapphire window is used as substrate. The deposition pattern on the window indicates up down and toroidal asymmetry. In the 5 h 16 min discharge, the thickness of the deposited layer increased monotonically with time and its deposition rate is ∼1.5 × 1016 Mo m−2 s−1. In the low density and long duration discharge, the Mo deposition rate on the window depends on the ratio of Mo flux to hydrogen flux.

Oxygen impurity behaviors of one long duration discharge and repetition of short duration discharges have been investigated in TRIAM-1M. In the former case, the OII line intensity divided by the line averaged electron density, which is considered as a monitor of oxygen concentration on the plasma facing surface (PFS), decreased with the time constant, τd, of 30–50 s during the discharge due to the hydrogen flux to PFS. In the latter case, τd is in the range of 70–600 s. There exists a big difference of global behavior of oxygen impurity between both cases. The difference seems to result from the absence or presence of the interval time between the discharges. The oxygen concentration on PFS increases during the interval time due to adsorption of H2O. The time constant of the increase in the oxygen concentration is evaluated to be about 5500 s from Langmuir adsorption isotherms analysis.

A diagnostic technique to study the global structure of the recycling and impurity (molybdenum) influx from the plasma facing components is proposed and is tested using the three kinds of perturbations (gas puffing, transport oscillation, and localized heat deposition). Balmer line intensities I H α , charge exchange flux ΓCX and neutral molybdenum line IMoI are measured and their correlations are analyzed with response to the perturbation parameters ( I H α at the gas port, density ne, and hot spot temperature Thot). A simple model calculation is done to understand these correlations. It is found that the phase reversal of ΓCX with respect to ne modulation is well reproduced and a critical density exists for the phase reversal of IMoI. The evaporation Mo flux evaluated with measured Thot is also compared with enhanced IMoI for the heat load perturbation and it contribution to the total content of Mo ions is evaluated by ∼30% increment.

The observation of dusts in plasmas was carried out by high speed camera in full non-inductive lower hybrid current drive (LHCD) plasma on TRIAM-1M. The velocities of dusts were 10–50 m/s. The number of dust generated per second increased with the discharge duration in the range of 20–57 s. This suggests that a part of dusts were generated from a movable limiter whose the surface temperature increases with the discharge duration. Dusts were coming from various directions even close to the movable limiter. Dusts were collected in the vacuum vessel by use of a kind of cleaner and the composition and the size of dust were examined by Scanning Electron Microscope (SEM). Dust size was several μm and composition was Molybdenum mixed with small amount of elements of stainless metal. The poloidal distribution of the collected mass of dusts was almost uniform.

A sheet thermal Li beam to study the density contour near X-point and divertor strike points has been developed for the spherical tokamak CPD. The CCD camera with a time resolution of 1 ms and spatial resolution of ∼1 mm can record two-dimensional images of LiI resonance line (300 mm × 500 mm). The performance of the sheet beam is absolutely calibrated by a quartz crystal monitor. The Li flux of 10 18 –10 19 m −2 s −1 is achieved near the X-point. The sheet characteristics of beam width and uniformity are also confirmed. This technique is applied during plasma initiation and electron cyclotron heating phase of plasma in a simple torus with a small vertical field. The formation of vertically stretched plasma at the position of the cyclotron resonance is clearly found. The expansion process towards the low field side is observed and an over dense plasma (>1 × 10 18 m −3 ) is obtained. A model calculation of LiI emission with density range of 1–5 × 10 18 m −3 agrees fairly well with the observations. Over dense plasma formation is also discussed.

In JT-60U, Xe gas has been injected into reversed shear plasmas with internal transport barriers. During these discharges, spectra from highly ionized Xe atoms have been observed in a wavelength range of 4–16 nm. The observed spectra have been analyzed by calculating theoretical spectra for Xe XXXVII–XLV 3s–3p and 3p–3d transitions with relativistic atomic structure codes, a collisional radiative model, and an impurity transport code. Several lines for Xe XLI and XLII have been newly identified. Soft X-ray emission profiles have also been analyzed, and the results showed that the Xe ions accumulated inside the internal transport barrier.

Tokamak operation has been performed under the localized plasma wall interaction conditions in TRIAM-1M, using a water cooled rail movable limiter (ML) made of Molybdenum. The limiter surface temperature dependence on hydrogen recycling and neutral molybdenum impurity production behaviour has been studied using visible as well as infrared spectroscopy during low power long pulse and high power short pulse discharges. In these experiments it is considered that escaped energetic electrons are lost mainly on ML and localised heat deposition makes a ‘hot spot’ on ML. It has been observed that H 2 , H α and MoI intensities critically depend on the hot spot temperature ( T hot ) and enhanced recycling due to localized PWI on ML can fuel the discharge without any external fueling source.

Calorimetric measurements using the temperature increment of cooling-water were carried out to estimate the heat load distribution on the plasma facing components (PFCs) in the limiter discharges on TRIAM-1M. Line averaged electron density, ne, and LH power, PLH, dependences of the heat load on PFCs were measured. The heat load on the limiters was proportional to n e 1.5 in the range of ne = 0.2–1.0 × 1019 m−3 and P LH 1 in the range of PLH = 0.005–0.09 MW. For PLH > 0.1 MW, the plasma transition to an enhanced current drive (ECD) mode appeared and the ne dependences on the heat load on the limiter moderated. This indicates that the heat flux to scrape-off layer (SOL) region was reduced due to the improvement of the plasma confinement. The up–down asymmetry of the heat load on the vacuum vessel was enhanced in the ECD mode, which may be caused by the increasing of the direct loss of energetic electrons.

Hydrogen particle behavior, especially H 2 molecule behavior, has been studied spectroscopically in attached and detached divertor plasmas of JT-60U. The decay lengths of the H 2 Fulcher line intensity in attached and detached divertor plasmas were roughly 1 cm and 4 cm, respectively. The fall in intensity of the H 2 Fulcher lines with distance from the divertor plates was reproduced by calculation using a neutral transport and a collisional radiative model code. Molecular assisted recombination was estimated to be as important as H + –e recombination in a detached divertor plasma.

In a collaboration of eight experiments the dependence of the chemical erosion yield of carbon on the ion flux, Φ , was established to Φ −0.54 at high ion fluxes. With this flux dependence a comprehensive description for chemical erosion is available as function of energy, temperature and flux. With this description the erosion and re-deposition of carbon in the ITER divertor can be calculated using the ITER steady-state plasma scenario and the ERO code. The resulting gross and net erosion rates during steady-state phase of discharges are compared to previous estimates using a constant erosion yield of 1.5%. The use of the complete parameter dependence results in an order of magnitude lower erosion, and, accordingly, of the T codeposition inventory.

Three reciprocating Mach probes were installed at the high-field-side (HFS) baffle, low-field-side (LFS) midplane and just below the X-point in JT-60U tokamak in order to investigate the SOL flow pattern. Profiles of particle fluxes produced by parallel SOL flow and Er×B-drift flow were evaluated from Mach number, electron temperature, density and floating potential. The drift particle flux was dominant near the separatrix, while it became smaller than the parallel particle flux at the outer flux surfaces. Total particle fluxes towards HFS and LFS divertors were investigated at various plasma densities. The drift flux was comparable to the parallel flux at relatively low densities, while the parallel flux became dominant at high densities. Drift flux in the private flux region was also evaluated, and it contributed to produce in–out asymmetries in the divertor ion flux and particle recycling under attached divertor condition.