Initial Fulcher band observations from high resolution spectroscopy in the MAST-U divertor

Abstract

High resolution D 2 ∗ Fulcher band spectroscopy was used in the MAST-U divertors during Super-X and (shorter-legged) elongated divertor density ramps with D 2 fuelling from the mid-plane high-field side. In the Super-X case, the upper divertor showed ground state rotational temperatures of the D 2 molecules increasing from ~6000 K, starting at the detachment onset, to ~9000 K during deepening detachment. This was correlated with the movement of the Fulcher emission region towards the X-point, which is in turn correlated with the movement of the ionisation source. The increase in rotational temperature occurred throughout the divertor except near the divertor entrance, where ionisation was still the dominant process. Qualitative agreement was obtained between the lower and upper divertor. Similar rotational temperatures were obtained in the elongated divertor before the detachment onset, although the increase in rotational temperature during detachment was less clearly observed as less deep detachment was obtained. The measured vibrational distribution of the upper Fulcher state does not agree with a ground state Boltzmann distribution but shows a characteristically elevated population in the ν = 2 and ν = 3 bands in particular; which is strongly correlated to the rotational temperature.

Tokamak divertor plasma emulation with machine learning

“…Predictive SOLPS-ITER [9] simulations have shown that the characteristic extended SOL magnetic field paths and increased flux expansion-which lead to increased radiative cooling and increased plasma wetted area-of the Super-X divertor can drastically reduce exhaust particle and heat flux on divertor tiles [10][11][12]. Recent experimental results are in line with the SOLPS-ITER predictions, showing significantly reduced heat loading on the divertor target [13,14] and migration of hydrogenic [15,16] and impurity [16] radiation fronts upstream of the target. The Super-X divertor configuration also expands the parameter region in which stable diverted plasmas can be obtained [14,17], which could enable longer pulses and improved core confinement.…”

Hydrogen isotope effects on recombination dominant plasmas in NAGDIS-II

“…where, I ki is the spectral intensity of the optical emission from the upper-level n = k to the lower-level n = i, λ ki is the wavelength of the spectral emission line, g k is the statistical weight of the upper level and A ki is the Einstein coefficient for spontaneous emission. The Q-branch of the Fulcher-α band for the hydrogen molecular is a suitable option for obtaining the rovibrational population due to its relatively strong spectral intensity and minimal perturbations [21,22]. The Q-branch comprises the rovibrational spectral transitions from the d 3 Π − u state to the a 3 Σ + g state.…”