High power neon seeded JET discharges: Experiments and simulations

A series of neon seeded JET ELMy H-mode pulses is considered from the modeling as well as from the experimental point of view. For two different Ne seeding rates and two different D puffing gas levels the heating power, Pheat, is in the range 22–29.5 MW. The main focus is on the numerical reconstruction of the total radiated power (which mostly depends on the W concentration) and its distribution between core and divertor and of Zeff (which mostly depends on the Ne concentration). To model self-consistently the core and the SOL two input parameters had to be adjusted case by case: the SOL diffusivity, DSOL, and the core impurity inward pinch, vpinch. DSOL had to be increased with increasing ΓNe and the level of vpinch had to be changed, for any given ΓNe, according to the level of Pheat: it decreases with increasing Pheat. Since the ELM frequency, fELM, is experimentally correlated with Pheat, (it increases with Pheat) the impurity inward pinch can be seen as to depend on fELM. Therefore, to maintain a low vpinch level (i.e. high fELM) ΓNe/Pheat should not exceed a certain threshold, which slightly increases with the ΓD puffing rate. This might lead to a limitation in the viability of reducing the target heat load by Ne seeding at moderate ΓD, while keeping Zeff at acceptably low level.