Chemical erosion of carbon at ITER relevant plasma fluxes:results from the linear plasma generator Pilot-PSI

\u3cp\u3eThe chemical erosion of carbon was investigated in the linear plasma device Pilot-PSI for ITER divertor relevant hydrogen plasma flux densities 10 \u3csup\u3e23\u3c/sup\u3e < Γ < 10\u3csup\u3e25\u3c/sup\u3e m\u3csup\u3e-2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e. The erosion was analyzed in situ by optical emission spectroscopy and post mortem by surface profilometry. The experiments indicate a threshold for the absolute carbon erosion rate as a function of plasma temperature T\u3csub\u3ee\u3c/sub\u3e around 0.7 eV, a peak of the surface temperature around 550 °C, and no dependence on plasma flux density. The latter implies a flux dependence of the chemical erosion yield as Γ\u3csup\u3e-1\u3c/sup\u3e. The value of the chemical erosion yield at the surface temperature of maximum erosion and Γ = 1 × 10\u3csup\u3e24\u3c/sup\u3e m\u3csup\u3e-2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e was 0.9% for T\u3csub\u3ee\u3c/sub\u3e < 0.5 eV as determined by surface profilometry.\u3c/p\u3

Production of high transient heat and particle fluxes in a linear plasma device

We report on the generation of high transient heat and particle fluxes in a linear plasma device by pulsed operation of the plasma source. A capacitor bank is discharged into the source to transiently increase the discharge current up to 1.7 kA, allowing peak densities and temperature of 70×1020 m-3 and 6 eV corresponding to a surface power density of about 400 MW¿m-2

Tritium control techniques in ITER by ammonia injection

A technique based on ammonia injection in the afterglow region of the divertor plasma is proposed for the inhibition of tritium/carbon co-deposits in remote areas of ITER when operated with carbon-based divertor targets. Supporting experiments in the PILOT-PSI divertor simulator plasma device and in a RF methane plasma with afterglow ammonia injection are described. The potential of ammonia glow discharges for the removal of carbon layer in easy to reach areas and in gaps is also addressed, thus opening the possibility of an integrated tritium control scenario with water-free chemical products in carbon-based divertor operation during the active phase of ITER. © 2011 Elsevier B.V. All rights reserved

Chemical erosion of different carbon composites under ITER-relevant plasma conditions

\u3cp\u3eWe have studied the chemical erosion of different carbon composites in Pilot-PSI at ITER-relevant hydrogen plasma fluxes (∼10\u3csup\u3e24\u3c/sup\u3e m \u3csup\u3e-2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e) and low electron temperatures (T\u3csub\u3ee\u3c/sub\u3e∼1 eV). Optical emission spectroscopy on the CH A-X band was used to characterize the chemical sputtering. Fine grain graphite (R 6650, SGL Carbon Group), ITER-reference carbon fiber composite material (SNECMA NB31 and NB41; Dunlop 3D), nano- and micro-crystalline diamond coatings on molybdenum and SiC (Silit® SKD Reaction-Bonded, Saint-Gobain Ceramics) were compared. The chemical sputtering was similar for the different composites under comparable plasma conditions, except for SiC, which produced a ten times lower rate. The CH emission was constant at electron temperatures T\u3csub\u3ee\u3c/sub\u3e>1 eV and ion fluxes ranging between 10\u3csup\u3e23\u3c/sup\u3e and 10\u3csup\u3e24\u3c/sup\u3e m\u3csup\u3e- 2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e, but decreased at lower temperatures. This decrease is possibly due to changes in the excitation of CH and not due to a change in the chemical erosion rate.\u3c/p\u3