In situdeuterium inventory measurements of a-C:D layers on tungsten in TEXTOR by laser induced ablation spectroscopy

Abstract

Laser induced ablation spectroscopy (LIAS) is a diagnostic to provide temporally and spatially resolved in situ measurements of tritium retention and material migration in order to characterize the status of the first wall in future fusion devices. In LIAS, a ns-laser pulse ablates the first nanometres of the first wall plasma-facing components into the plasma edge. The resulting line radiation by plasma excitation is observed by spectroscopy. In the case of the full ionizing plasma and with knowledge of appropriate photon efficiencies for the corresponding line emission the amount of ablated material can be measured in situ. We present the photon efficiency for the deuterium Balmer α-line resulting from ablation in TEXTOR by performing LIAS on amorphous hydrocarbon (a-C:D) layers deposited on tungsten substrate of thicknesses between 0.1 and 1.1 µm. An experimental inverse photon efficiency of [ D XB ] a-C:D → LIAS D D α (EXP) = 75.9 ± 23.4 was determined. This value is a factor 5 larger than predicted values from the ADAS database for atomic injection of deuterium under TEXTOR plasma edge conditions and about twice as high, assuming normal wall recycling and release of molecular deuterium and break-up of D 2 via the molecular ion which is usually observed at the high temperature tokamak edge (T e > 30 eV).

Material testing facilities and programs for plasma-facing component testing

“…One crucial aspect of all these efforts are in situ diag nostics, to measure erosion fluxes [210][211][212], but also mat erial inventory like hydrogen retention or material composition of redeposited layers [95,[213][214][215][216][217][218][219][220][221][222].…”

“…When trying to extrapolate to future devices also the in situ assessment of deposition and fuel retention in materials is of crucial importance [95,214,217]. Utilizing lasers as means of in situ release mechanism for fuel species was intensely studied especially at TEXTOR [218,219,222] with a focus on a:C-D layers-co-deposits with carbon [215,216,220,221]. This work includes studies on tungsten materials even though main mechanisms here include implantation and hence require melting of the surfaces to release the fuel [355].…”

Dimensional effects in analysis of laser-induced-desorption diagnostics data

“…The laser techniques for the analysis of the tokamak first wall are based on using the laser radiation to remotely heat the surface of the tokamak tiles and register either the radiation signal from the gas cloud/plasma plume formed near the target surface or the particle flux from the tile surface. A broad range of methods such as the Laser-Induced Breakdown Spectroscopy (LIBS) [7,8,11,[13][14][15][16][17][18][19][20][21][22], Laser-Induced Ablation Light [6,9,[23][24][25][26] /Mass [27][28][29][30][31] Spectroscopy (LIAS/LIA-QMS), and also the Laser-Induced-Desorption Light [6,32,33] and Mass [10,26,31,32,[34][35][36][37][38][39][40] Spectrometry (LIDS/LID-QMS) were proposed for analysis of tritium content in the tokamak plasma facing materials.…”

Possibility of using machine learning methods to reconstruct solid body parameters during laser-induced desorption analysis

“…Currently, for remote monitoring of the tritium concentration in the reactor wall, the laser-based methods are proposed, which include laser-induced breakdown (LIBS) [3][4][5][6][7][8], ablation (LIAS) [9][10][11][12][13], desorption (LIDS) [9,[14][15][16][17] spectroscopy, as well as the method of laser-induced desorption-quadrupole mass-spectrometry (LID-QMS) [15,[18][19][20][21][22][23] (and its ablation counter-part, LIA-QMS [24][25][26][27]). The methods are based on local heating of the sample surface layers (to the depth up to several micrometers) by short laser pulses and further measuring of the power/spectral composition of the emitted radiation (LIBS/LIAS/LIDS) or the mass flow of the desorbed gas/ablated material (LID-QMS/LIA-QMS).…”