• Energy Research

Toroidal and poloidal flows of injected N+ ions were measured in the high-field side (HFS) scrape-off layer (SOL) of ASDEX Upgrade by Doppler spectroscopy with different degrees of HFS divertor detachment. In high-recycling conditions, the results suggest reversed parallel N+ flow away from the inner divertor in the near SOL close to the separatrix, while the flow is towards the inner divertor throughout the SOL in detached conditions. The measured poloidal N+ flows were directed away from the HFS divertor in the near SOL for all density cases. Divertor plasma oscillations, characterized by momentary peaking of the HFS target ion flux and decrease of the HFS SOL density, were observed slightly before the roll-over of the ion saturation current to the HFS target and lead to an increase in the N+ flow towards the HFS divertor. SOLPS and ERO simulations of the experiment predict entrainment below 50% between the velocities of N+ and D+ ions, suggesting that N+ ions are quantitatively a limited proxy for measuring D+ flows. ERO simulations show significantly higher entrainment for higher ionization states, e.g., N2+ and N3+.

Toroidal and poloidal flows of injected N+ ions were measured in the high-field side (HFS) scrape-off layer (SOL) of ASDEX Upgrade by Doppler spectroscopy with different degrees of HFS divertor detachment. In high-recycling conditions, the results suggest reversed parallel N+ flow away from the inner divertor in the near SOL close to the separatrix, while the flow is towards the inner divertor throughout the SOL in detached conditions. The measured poloidal N+ flows were directed away from the HFS divertor in the near SOL for all density cases. Divertor plasma oscillations, characterized by momentary peaking of the HFS target ion flux and decrease of the HFS SOL density, were observed slightly before the roll-over of the ion saturation current to the HFS target and lead to an increase in the N+ flow towards the HFS divertor. SOLPS and ERO simulations of the experiment predict entrainment below 50% between the velocities of N+ and D+ ions, suggesting that N+ ions are quantitatively a limited proxy for measuring D+ flows. ERO simulations show significantly higher entrainment for higher ionization states, e.g., N2+ and N3+.

SOLPS 5.0 simulations assuming convection-dominated radial ion transport show qualitative and quantitative agreement with measurements of detached high-field side (HFS) divertor conditions for unseeded low-power L-mode plasmas in ASDEX Upgrade, while simultaneously maintaining a reasonable match to the density and temperature measurements at the low-field side (LFS) and HFS midplanes within the scatter of the data. The decreased diffusive transport from the high-density region in the HFS divertor volume across the separatrix into the core enables spatial extension of the high-density front to above the X-point in agreement with spectroscopic measurements. The suppressed ion fuelling from this region into the core plasma allows increasing the neutral D 2 fuelling to experimental levels, leading to agreement with the measured sub-divertor neutral fluxes within 30%. Detachment of the HFS divertor is observed as a significant decrease of the target ion flux and as reproduction of the characteristic roll-over behaviour of the integrated target ion current at increasing upstream density. EUROfusion Consortium 633053

SOLPS 5.0 simulations assuming convection-dominated radial ion transport show qualitative and quantitative agreement with measurements of detached high-field side (HFS) divertor conditions for unseeded low-power L-mode plasmas in ASDEX Upgrade, while simultaneously maintaining a reasonable match to the density and temperature measurements at the low-field side (LFS) and HFS midplanes within the scatter of the data. The decreased diffusive transport from the high-density region in the HFS divertor volume across the separatrix into the core enables spatial extension of the high-density front to above the X-point in agreement with spectroscopic measurements. The suppressed ion fuelling from this region into the core plasma allows increasing the neutral D 2 fuelling to experimental levels, leading to agreement with the measured sub-divertor neutral fluxes within 30%. Detachment of the HFS divertor is observed as a significant decrease of the target ion flux and as reproduction of the characteristic roll-over behaviour of the integrated target ion current at increasing upstream density. EUROfusion Consortium 633053

The roles of the molecularly assisted ionization (MAI), recombination (MAR) and dissociation (MAD) reaction chains with respect to the purely atomic ionization and recombination processes were studied experimentally during detachment in low-confinement mode (L-mode) plasmas in JET with the help of experimentally inferred divertor plasma and neutral conditions, extracted previously from filtered camera observations of deuterium Balmer emission, and the reaction coefficients provided by the ADAS, AMJUEL and H2VIBR atomic and molecular databases. The direct contribution of MAI and MAR in the outer divertor particle balance was found to be inferior to the electron–atom ionization (EAI) and electron–ion recombination (EIR). Near the outer strike point, a strong atom source due to the D2+-driven MAD was, however, observed to correlate with the onset of detachment at outer strike point temperatures of Te,osp=0.9–2.0 eV via increased plasma-neutral interactions before the increasing dominance of EIR at Te,osp< 0.9 eV, followed by increasing degree of detachment. The analysis was supported by predictions from EDGE2D-EIRENE simulations which were in qualitative agreement with the experimental observations.