Modelling of deuterium emission in high density divertor plasmas in JET

Simulations of neutral deuterium emission from high density Ohmic and L-mode JET divertor discharges with the EDGE2D/NIMBUS codes are presented. At high density the codes fail to reproduce quantitatively the steady increase of divertor D-0 emission with rising plasma density observed in the experiment. However, good agreement is obtained with the measured D-gamma/D-alpha ratio in inner and outer divertor despite the total plasma volume recombination being small in the simulations. The asymmetry between inner and outer divertor detachment is found to depend on the strength of the charge exchange momentum losses. Recombination alone is not sufficient to obtain strong detachment in the inner divertor. Measurements of Ly(beta)/D-alpha emission profiles across the JET divertor show signs of Lyman radiation reabsorption in the inner divertor at high density. The first attempt at including divertor plasma opacity corrections self-consistently in EDGE2D/NIMBUS simulations of high density JET L-mode discharges is presented. The effect of opacity on the simulated deuterium emission and on the 2D plasma solution is discussed. (C) 1999 JET Joint Undertaking, published by Elsevier Science B.V. All rights reserved.