Physical and engineering aspects of RF plasma cleaning developed for actively cooled first mirror serving as grounded DC-coupled electrode are under consideration. Feasibility of the water-cooling ...lines implemented as the coaxial notch filter for ITER in-vessel diagnostic mirrors was demonstrated for Capacitively Coupled Radio Frequency (CCRF) discharge in neon at 1–10 Pa. The impinging ions energy as a function of absorbed RF power was measured for both the DC-coupled and -decoupled schemes. Sputtering yield variation over rectangular surface of stainless steel mirror was studied experimentally. The measured sputtering yield profiles were found to be in qualitative agreement with the RF plasma numerical simulations. It was demonstrated that Al/Al2O3 used as Be/BeO proxy can be removed from the water cooled mirror surface by 100 eV neon ions with the use of the notch filter. The 14 h plasma exposure didn’t affect the mirror reflectivity.
The development of the first mirror cleaning and recovery system is one of the challenges for all optical diagnostics in ITER. This study is focused on capacitively coupled radio frequency (CCRF) ...discharge as a promising method for removal of metal deposits. The physical aspects of the RF discharge application are discussed with a focus on implementation under ITER conditions. The effective sputtering rates of Be, W and Mo were calculated as a function of applied frequency and absorbed power for noble gases-He, Ne, Ar, Kr, Xe, taking into account complex shape of the ion energy distribution function in the electrode sheaths. Helium is shown to be a good candidate for cleaning Mo mirrors from Be deposits in the frequency range ∼80-100 MHz and pressure of a few Pa.
Formation of dust particles and clusters is observed in almost every modern thermonuclear facility. Accumulation of dust in the next generation thermonuclear installations can dramatically affect the ...plasma parameters and lead to the accumulation of unacceptably large amounts of tritium. Experiments on collection of dust particles by a model of electrostatic probe developed for collection of metallic dust at ITER are described in the article. Experiments on the generation of tungsten dust consisting of flakes formed during the destruction of tungsten layers formed on the walls of the plasma chamber sputtered from the surface of the tungsten target by plasma ions were conducted. The nature of dust degassing at elevated temperatures and the behavior of dust in an electric field were studied. The results obtained are compared with the results of the experiments with dust consisting of crystal particles of simple geometric shapes. The effectiveness of collection of both types of dust using the model of an electrostatic probe is determined.
The paper presents a short revue of the study of not been investigated specific features of hydrogen trapping in graphite occurring as the results of inelastic interaction of impinging ions with ...carbon materials (potential trapping). The influence of potential mechanism on different regularities of hydrogen trapping are considered. Among them there is trapping dependence on irradiating ion current density, ion energy, irradiation fluence, temperature of the investigated samples and oxygen addition in the plasma.
The paper describes a new laboratory stand constructed for film deposition and for testing of deposited films and materials under pulsed and continuous heat load, ion and electron irradiation. The ...films are formed on substrates by atoms of target materials as a result of their sputtering by ions of argon plasma. The ion energy and ion flux can be varied independently. This enables the deposition of coatings with variable composition over thickness or of multi-layer coatings. Testing of materials is carried out in plasma under ion or electron irradiation by biasing the tested sample negatively or positively, respectively. The energies of ions or electrons can be varied up to 25 keV. The applied power can reach 4000 W (40 MW/m2 power density in the case of a 1-cm2 sample) in both continuous and pulsed regimes. In pulsed regime, pulses of 1 - 99% duty cycle at 0 - 500 Hz can be applied to the sample. The pulsed particle load can be combined with a continuous load. The size of the tested sample must not exceed 100 mm in diameter. The heat flux can irradiate the whole sample or be focused at its center (minimum spot of ~ 4mm2). Heating of the samples up to 2800 K is possible. At the same time, the backside of the tested sample could be actively cooled. This paper presents the results of deposition and testing of a B4C coating on tungsten and tungsten testing.
The paper presents results of the experiments devoted to investigation of hydrogen trapping in deposited carbon films under various implantation conditions (residual gas, hydrogen atmosphere, ...accompanying plasma irradiation). Effect of consequent deuterium irradiation on hydrogen trapping is also studied. Influence of such deposition parameters as deposition rate, residual gas pressure, hydrogen pressure, plasma ions energy, substrate material on hydrogen trapping is discussed. A conclusion about trapping mechanism in growing carbon layers is made.
Abstract
The challenges of large-scale mirror design for in-vessel collection system of ITER Divertor Thomson Scattering (DTS) are under consideration. These are the mirrors located out-of-line ...vision of fusion plasma (so called “second mirrors” i.e. not First Mirrors) with high-reflective Ag-based coating. The paper outlines: approaches providing optical surface shape and angular position stability; Ag coating applicability in nuclear irradiation, ITER in-vessel application and its resistance to Steam Ingress. Although, this assessment and the proposed solutions are considered in terms of ITER DTS compatibility, they may also appear to be of some use in other ITER diagnostics and in diagnostics of other fusion devices.
The effect of ion irradiation and deposited yttrium-oxide layers on deuterium desorption from titanium deuteride is studied. The features of deuterium desorption during the interaction of hydrogen ...ions with a titanium-deuteride layer are revealed. It is shown that gas desorption decreases both under hydrogen-ion irradiation with energies of <1000 eV and the deposition of an yttrium oxide layer.
Mirrors will be used as first plasma-viewing elements in optical and laser-based diagnostics in ITER. Deterioration of the mirror performance due to e.g. sputtering of the mirror surface by plasma ...particles or deposition of impurities will hamper the entire performance of the affected diagnostic and thus affect ITER operation. The Specialists Working Group on First Mirrors (FM SWG) in the Topical Group on Diagnostics of the International Tokamak Physics Activity (ITPA) plays an important role in finding solutions for diagnostic first mirrors. Sound progress in research and development of diagnostic mirrors in ITER was achieved since the last overview in 2009. Single crystal (SC) rhodium (Rh) mirrors became available. SC rhodium and molybdenum (Mo) mirrors survived in conditions corresponding to ~200 cleaning cycles with a negligible degradation of reflectivity. These results are important for a mirror cleaning system which is presently under development. The cleaning system is based on sputtering of contaminants by plasma. Repetitive cleaning was tested on several mirror materials. Experiments comprised contamination/cleaning cycles. The reflectivity SC Mo and Rh mirrors has changed insignificantly after 80 cycles. First in situ cleaning using radiofrequency (RF) plasma was conducted in EAST tokamak with a mock-up plate of ITER edge Thomson Scattering (ETS) with five inserted mirrors. Contaminants from the mirrors were removed. Physics of cleaning discharge was studied both experimentally and by modeling. Mirror contamination can also be mitigated by protecting diagnostic ducts. A deposition mitigation (DeMi) duct system was exposed in KSTAR. The real-time measurement of deposition in the diagnostic duct was pioneered during this experiment. Results evidenced the dominating effect of the wall conditioning and baking on contamination inside the duct. A baffled cassette with mirrors was exposed at the main wall of JET for 23,6 plasma hours. No significant degradation of reflectivity was measured on mirrors located in the ducts. Predictive modeling was further advanced. A model for the particle transport, deposition and erosion at the port-plug was used in selecting an optical layout of several ITER diagnostics. These achievements contributed to the focusing of the first mirror research thus accelerating the diagnostic development. Modeling requires more efforts. Remaining crucial issues will be in a focus of the future work of the FM SWG.
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