Molecular deuterium behaviour in tungsten divertor on JET

Abstract Molecular spectroscopy was used to observe molecular deuterium at the outer strike point of the new bulk tungsten JET divertor. The rotational and vibrational populations of the deuterium molecules in the ground state were determined from the deuterium Q-branches of Fulcher-α band emission ( d 3 Π u - → a 3 Σ g + ) in the 600–640 nm spectral range. For L-mode plasmas in the low recycling regime the molecular emission maximum is located in the vicinity of the strike point. The spatial profile of the emission was strongly modified during plasma detachment in both L- and H-mode plasmas. The rotational temperature of excited molecules reached 2760 K in L-mode. The vibrational population has a peculiarity: a remarkably high population of the d 3 Π u - ( v = 0) vibrational level indicating a non-Boltzmann vibrational distribution of D 2 in tungsten environment.