D. Specific Contributions of the Partners within the IEA Implementing Agreement
D.1. Japan
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Penning Gauge Spectroscopy on LHD
H. Funaba, National Institute for Fusion Science
Aims:
(1) Partial pressure measurement of hydrogen (H), helium (He) or noble gases (Ne, Ar, Kr, Xe) in the vacuum vessel of the Large Helical Device (LHD).
(2) Partial pressure measurement in the high gas pressure region up to about 0.1 Pa where the mass analyzer cannot be used.
Work performed:
(1) Installation of the detector system. The penning gauge of LHD is located on an upper port (2.5U) of the vacuum vessel.
(2) Measurement during the main discharges of LHD. The penning gauge spectroscopy was oper-ated during the main discharges of LHD including the 54 minutes discharge. The visible light from 580 to 730 nm was observed. The helium partial pressure could be detected after the dis-charge. But it was close to the detection limit during the long pulse discharges.
Work planned:
(1) Improvement of the optical system. The improvement of the optical system will be continued.
(2) Remote access of the obtained data will be possible in the next fiscal year.
(3) Data obtained during and after discharges will be analyzed and discussed mainly between M.
Lehnen and H. Funaba.
Millimetre-Wave Imaging Diagnostics
A. Mase, Kyushu University
Aims:
To develop a 2D-3D millimetre-wave imaging system for measurements of temperature and density profiles as well as fluctuations in magnetically confined plasmas.
Work performed:
(1) A new optical system for MIR (microwave imaging reflectometry) and ECEI (electron cyclo-tron emission imaging) has been fabricated and installed in LHD. Simultaneous experiments of MIR/ECEI have been performed using a new detector array and IF system.
(2) A notch filter with a rejection frequency of 140 GHz has been designed at UC Davis (UCD) and was fabricated using the electro fine forming (EF2) technique at Kyushu Hitachi Maxell, Ltd. A rejection of -32.5 dB at f = 140 GHz and less than 1 dB transmission loss in the pass band are obtained, which are better than those values from fabrication by the conventional etching proc-ess. The filter has been attached to the microwave imaging reflectometer (MIR) system at the TEXTOR tokamak, operated by the UCD-PPPL and FOM groups.
(3) Simulation studies of microwave imaging reflectometry have been performed. For the particular amplitude of fluctuations, the imaging reflectometer is found to be able to measure parameters of the fluctuations accurately if the width of the wave number spectrum Δkfluct is less than 0.2 k0, where k0 is the wave number of an incident wave, while the conventional reflectometer is able to measure accurately only if Δkfluct ≤ 0.1 k0. Therefore, the imaging reflectometer demonstrates a wider range of measurable parameters in comparison with the conventional system.
Work planned:
(1) Under the TEXTOR and US-Japan collaborating programme, the imaging system (ECEI and MIR) will be applied to LHD as well as to TEXTOR.
(2) The EF2 technology will be applied to the fabrication of imaging array antennas as well as notch filters.
Preliminary tests for the application of the BIXS system to ITER
M. Matsuyama and Y. Torikai, Toyama University
Aims:
To examine the effects of a strong radiation field on BIXS measurements.
Work performed:
The design of an in-situ system for tritium measurements was analysed and discussed. Results were presented on 7th International Symposium on Fusion Nuclear Technology held in May 2005 at To-kyo.
Work planned:
Further evaluation for ITER and/or LHD applications will be continued.
Behaviour of the magnetic structure of the SOL in TEXTOR with AC-DED
M. Sakamoto, Kyushu University
Aims:
(1) Establishment of the methodology for an analysis of the magnetic structure of the SOL with AC-DED in TEXTOR.
(2) Investigation of the behaviour of the magnetic structure of the SOL with AC-DED.
(3) Understanding of the relation between MHD phenomena of the core plasma and the SOL mag-netic structure.
Work performed:
Data analysis and preparation of a paper have been in progress on Hα signals which are measured at the poloidal limiter, the ALT-II limiter and at the divertor tiles. They are perturbed with the same frequency as that of the DED coil current.
Work planned:
The following works will be continued:
(1) Analysis of the magnetic structure of the SOL with AC-DED in TEXTOR.
(2) Investigation of the density dependence of the behaviour of the magnetic structure.
(3) Investigation of the dependence of the behaviour of the magnetic structure on the safety factor.
Excitation of Alfven eigenmodes (AEs) and impedance measurements using the DED coils
T. Shoji, Nagoya University; A. Tsushima, Yokohama National University; Y. Kikuchi, K.H. Finken, M. Lehnen, O. Zimmermann,FZJ; A.G. Elfimov, University of San Paulo
Aims:
(1) Superimpose RF currents (50 kHz – 1 MHz) on the DED coils to excite AEs.
(2) Study the characteristics of AEs with DED and additionally heated plasmas in TEXTOR.
(3) Get information about these plasmas such as the q-profile and energetic particles by measuring the AEs spectrum from the impedance of the DED coils.
Work performed:
(1) The system has been modified to superimpose RF currents (50 kHz – 1 MHz, < 2 A) on the DED coils in the 6/2-mode.
(2) The impedance measurement system addressing the DED coils has been tested under modified conditions.
(3) Preliminary measurements of the change in the spectrum of the RF voltage and current have been carried out.
Work planned:
(1) Impedance measurements for NBI and ICRF heated plasmas with the 6/2-mode arrangement.
(2) AEs wave detection by Mirnov coils and modes identification, wave damping.
(3) Study the effects of DED ergodization on AEs mode excitation.
Edge Plasma diagnostics
A. Tsushima, Yokohama National University
Aims:
(1) Measurement of the edge plasma.
(2) Study of the edge plasma transport.
Work performed:
(1) Design of an axisymmetric ion sensitive probe for usage in a tokamak edge plasma has been in progress.
(2) Facing double probe. Tests of a facing double probe have been carried out . Work planned:
(1) To improve design an axisymmetric ion sensitive probe for usage in a tokamak edge plasma.
Plasma wall interaction of low activation ferritic steel
K. Tsuzuki, JAERI
Aims:
Low activation ferritic steel is one of the candidates for the structure material of a fusion demonstra-tion reactor. However, it is a ferromagnetic material and the vacuum properties are worse than those of stainless steel. Thus, the compatibility of ferritic steel with plasmas is one of the critical issues.
The main purpose of this work is as follows:
(1) To examine the response of low activation ferritic steel under plasma exposure with spectro-scopic measurements.
(2) To examine the influence of (local) magnetic fields on PMI with heat and H emission profiles.
Work performed:
(1) The behaviour of melted layers has been analysed for ferritic steel test limiters.
(2) Results were presented on 7th International Symposium on Fusion Nuclear Technology held in May 2005 at Tokyo.
Work planned:
Additional experiments are not planned at present.
PMI studies related to high-Z materials in TEXTOR
Y. Ueda et al., Osaka University
Aims:
(1) Investigations of the behaviour of high-Z impurities in main and boundary plasmas.
(2) Understanding of local phenomena (sputtering, reflection redeposition, etc.) in front of the high-Z limiter surface.
(3) Examination of high-Z materials behaviour exposed to plasma heat load.
(4) Influence of the DED on impurity production and its local transport.
(5) Tritium distribution analysis of PFM tiles using the imaging plate technique.
(6) Simulation of PMI.
Work performed:
(1) New limiter with local heating capability
The new roof limiter made from isotropic graphite is being assembled. The most important fea-ture of it is a local heating capability. In this limiter, a small thin plate heater (BN plate heater, Tectra co.) is embedded. By using this limiter head it is possible to expose two samples with different temperatures to TEXTOR edge plasmas in the same drift side (ion drift side or elec-tron drift side).
(2) Modelling of erosion and deposition patterns on W and Ta limiters exposed to the TEXTOR edge plasma
The erosion and deposition patterns on W and Ta test limiters exposed to the TEXTOR deute-rium plasma containing a small amount of C impurity are simulated with the modified EDDY code. The EDDY code was modified to be able to simulate erosion and deposition pattern un-der actual test limiter conditions. In addition, ionization and dissociation processes of hydro-carbon molecules other than methane were included in the codes.
(3) Blistering experiments for W
Pure W and K doped W were exposed to the TEXTOR edge plasma to examine whether blis-tering takes place or not. The sample temperature was carefully controlled to be less than 500
°C, where blistering was observed in ion beam experiments. The samples were exposed to 12 OH shots and 8 NBI shots. The total fluence was in the order of 1024 m-2, enough for blistering
to appear in ion beam experiments. But no blistering was observed. The reason is under inves-tigation.
(4) Detailed observation of carbon redeposition patterns on W and Ta plates
In the previous W and Ta twin limiter experiments, carbon deposition patterns have been dif-ferent between Ta and W. But in this case, W and Ta sides were not exposed to the same edge plasmas, so the experimental results were unreliable. In 2004, however, W and Ta were placed on the same side of a graphite roof limiter in order to expose them to identical plasma condi-tions. After exposure to 12 OH shots and 8 NBI shots, different carbon deposition patterns have been observed. Detailed analysis will be done in future.
Work planned:
(1) Hydrocarbon gas puffing experiments through a limiter hole.
(2) Simultaneous plasma exposure to high-Z materials with different temperatures.
(3) Melt layer behaviour under high particle and heat flux.
(4) Artificial hot spot experiments with laser irradiation for dynamic retention measurements.
(5) Effects of the DED on the above (1-4).
(6) Local plasma parameter measurements by a Langmuir probe installed on a test limiter.
(7) Relation between limiter structures and high heat flux response.
(8) Simulation study of carbon redeposition patterns.
Tangentially viewing soft X-ray camera
S. Ohdachi et al., National Institute for Fusion Science
Aims:
(1) Direct detection of magnetic islands by the tangential projection of soft x-ray images from tor-oidally confined plasmas.
(2) Understanding of the mechanism of the generation and development of magnetic islands.
(3) Study of the relation between transport and magnetic islands.
Work performed:
(1) Development of the tomographic reconstruction code for the tangential imaging.
In order to study the images, e.g. those we obtained at DED experiments, we have been devel-oping tomographic reconstruction codes. From a single tangential view of the plasma, it is not possible to reconstruct a three-dimensional (3D) radiation profile. We assume that radiation along the magnetic field lines is constant and try to reconstruct a two-dimensional (2D) profile
on a poloidal plane. First, the video image is decomposed to one stationary component and fluctuating components using the singular value decomposition method (SVD). Then, the equi-librium magnetic field is determined from the stationary image; we select an equiequi-librium by which the best reconstruction can be made. Using this equilibrium magnetic field, the lines of sight are interpreted as the curved lines on the target poloidal plane. Thereby, the 3D-reconstruction problem is reduced to the well-known 2D problem. It is found that a method based on the truncated least square method using orthogonal components generated also by SVD is suitable for this kind of reconstruction. We have, therefore, successfully reconstructed 2D images on a poloidal plane. We have extended this code using flux coordinates so that we can employ it also in 3D equilibrium fields, e.g. in those of the Large Helical Device (LHD).
(2) Refinements of the camera system.
After the measurement on the TEXTOR tokamak on 2003, the camera system was moved to Japan and mounted on the LHD again with refinements. We replaced the fast framing video camera (KODAK 4540MX) with a new one (Vision Research: Phantom V7.0). We can expect about 10 bit of dynamic range now. Time for the data transfer is reduced to 5 min. (We can take data every two discharges in the LHD). With improved dynamic range, we got images dur-ing the minor internal disruption events in the 8th-9th experimental campaign. A deformation of the magnetic flux surface (m = 2,3) from the interchange MHD was found. Flattening of the profile is observed just after the largest deformation; magnetic reconnection with the deforma-tion might explain this observadeforma-tion.
In order to study the edge MHD activities, we are preparing to build a VUV telescope and a gas-puff imaging system on LHD, which will enable us to visualize the spatial structure of the edge MHD instabilities.
Work planned:
(1) Further data analysis using the reconstruction codes.
(2) Preparation of the re-installation of the refined camera system on the TEXTOR device in 2006.
D. PARTNERS OF THE IEATEXTORIMPLEMENTING AGREEMENT