High power neon seeded JET discharges: Experiments and simulations

Abstract

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, P heat , 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 Z eff(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, D SOL , and the core impurity inward pinch, v pinch . D SOL had to be increased with increasing Ne and the level of v pinch had to be changed, for any given Ne , according to the level of P heat : it decreases with increasing P heat . Since the ELM frequency, f ELM , is experimentally correlated with P heat , (it increases with P heat ) the impurity inward pinch can be seen as to depend on f ELM . Therefore, to maintain a low v pinch level (i.e. high f ELM ) Ne / P heat should not exceed a certain threshold, which slightly increases with the D puffing rate. This might lead to a limitation in the viability of reducing the target heat load by Ne seeding at moderate D , while keeping Z effat acceptably low level.