plasma-material interactions; plasma diagnostic techniques; laser induced breakdown spectroscopy; laser induced ablation spectroscopy;FUSION DEVICES; COMPONENTS

A laser based method combined with spectroscopy, such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy , is a promising technology for plasma-wall interaction studies. In this work, we report the development of in situ laser-based diagnostics for the assessment of static and dynamic fuel retention on the first wall without removing the tiles between and during plasma discharges in the Experimental Advanced Superconducting Tokamak . The fuel retention on the first wall was measured after different wall conditioning methods and daily plasma discharges by in situ LIBS. The result indicates that the LIBS can be a useful tool to predict the wall condition in EAST. With the successful commissioning of a refined timing system for LIAS, an in situ approach to investigate fuel retention is proposed.

laser-induced breakdown spectroscopy; plasma wall interaction; fuel retention; deposition; erosion;

Laser-induced breakdown spectroscopy is a well-established elemental composition analysis method as well as one of the most promising candidates for in situ first wall diagnosis of fusion devices. In this work, limiter graphite tiles, which were exposed in the initial operational phase of the Wendelstein 7-X stellarator to He and H plasma, are analyzed ex situ by LIBS employing a picosecond pulsed laser for the first time and compared with post mortem analysis techniques. Depth profiles of each element and 2D profile of the ratio of H and C atoms on the surface are investigated. Both H content and retention depth on the deposition dominated zone are higher than on the erosion dominated zone due to the formation of C-H co-deposition layer. The results from LIBSare in agreement with those from the cross-sectional scanning electron microscopic image and electron dispersive x-ray spectroscopy.

laser induced breakdown spectroscopy; spatial regularities of the laser-induced plasma plume; detection of hydrogen isotopes;EROSION/DEPOSITION; SPECTROSCOPY

ITER plans foresee the quantitative diagnostics of fuel retention in reactor walls at nearatmospheric pressures. Using laser induced breakdown spectroscopy for this purpose assumes a reliable resolving of Balmer a-lines of hydrogen isotopes in spectra of plasma produced by focused laser radiation onto the target surface. To develop LIBS for quantitative diagnostics of fuel retention during the maintenance breaks of ITER, the effect of background gas pressure on the laser-induced plasma characteristics has been studied. The background pressure limits the expansion rate of plasma and as a result it leads to higher plasma concentrations. At the same time the limiting factor of the resolving of hydrogen isotope lines is the lines broadening by Stark effect, which is the function of electron concentration. The resolving of lines become possible recording spectra at longer delay times after the laser pulse. On the other hand, at longer delays the signal-to-noise ratio decreases. As a compromise, we found that at atmospheric pressure and at delay times > 2000 ns, a fitting of H a and D a lines by Voigt contours allows a reliable discrimination of these lines.

Ambient gas; Magnetic field; LIBS; EAST; ICRF wall cleaning;TRANSVERSE MAGNETIC-FIELD; INDUCED PLASMA SPECTROSCOPY; OPTICAL-EMISSION; PLUME; PERFORMANCE

In this paper, laser-induced breakdown spectroscopy (LIBS) under magnetic field condition has been studied in laboratory and EAST tokamak. The experimental results reveal that in helium ambient gas, the magnetic field significantly enhances the LIBS signal intensity (similar to 3 times). The effect of time delay and laser fluence on the intensity of LIBS has been investigated for optimizing the signal to background ratio (S/B). The developed LIBS approach has been applied to monitor the cleaning performance of the first wall in the fusion device of EAST using the ion cyclotron range of frequency (ICRF). The experimental results demonstrate that the cleaning performance for Li/D co-deposition layer is effective under helium ambient gas. The removing rate of Li on the surface of W tile is faster than that on Mo tile in He-ICRF cleaning and the D/(D + H) ratio on Mo tile is higher by similar to 1.2 times than that on W tile. This work would indicate the feasibility of using LIBS to monitor the wall cleaning processes in EAST tokamak. (C) 2017 Elsevier B.V. All rights reserved.

Deposition; PFC tile; HL-2A; LIBS; QMB;DIVERTOR TILES; ASDEX UPGRADE; CARBON; JET; EROSION/DEPOSITION; CODEPOSITION; EROSION; WALL

Since the divertor geometry of a tokamak has a strong impact on the material erosion and deposition on the wall and HL-2A has a unique divertor configuration, it is necessary to investigate the material deposition pattern in HL-2A although a few results on other tokamakS have already been published. In this paper, tiles retrieved from the vessel are analyzed ex-situ by sIMS, SEM and laser-induced breakdown spectroscopy (LIBS). And deposition behind the lower divertor is in-situ measured by a quartz crystal microbalance (QMB). The deposition in HL-2A displays a complex pattern and clear localization characteristic. The thickness of the deposition layer varies in the range of 0-4 mu m. And in-situ diagnostic of QMB indicates that the average thickness of the deposition layer per pulse is over ten nanometers. In addition, the results imply that Si, Fe and D have different behaviors during the material deposition in HL-2A. (C) 2016 Elsevier B.V. All rights reserved.