Fuel retention studies with the ITER-Like Wall in JET

Abstract

Abstract:JET underwent a transformation from a full carbon-dominated tokamak to a full metallic device with the ITER-like wall combination for the activated phase with Beryllium main chamber and Tungsten divertor. The ITER-Like Wall (ILW) experiment at JET provides an ideal test bed for ITER and shall demonstrate as primary goals the plasma compatibility with metallic walls and the reduction in fuel retention. We report on a set of experiments ( = 2.0 , = 2.0 − 2.4 , = 0.2 − 0.4) in different confinement and plasma conditions with global gas balance analysis demonstrating a strong reduction of the long term retention rate by a factor ten with respect to carbon references. All experiments have been executed in a series of identical plasma discharges in order to achieve maximum plasma duration until the analysis limit of the active gas handling system has been reached. The composition analysis shows high purity of the recovered gas, typically 99% D. For typical L-mode discharges ( = 0.5 ), type III ( = 5.0 ), and type I ELMy H-mode plasmas ( = 12.0 ) a drop of the retention rate normalised to the operational time in divertor configuration has been measured from 1.27 × 10 has been obtained with the ILW. The observed reduction by one order of magnitude confirms the expected predictions concerning the plasma-facing material change in ITER and widens the operation without active cleaning in the DT phase in comparison to a full carbon device.

Study of physical and chemical assisted physical sputtering of beryllium in the JET ITER-like wall

“…The predicted advantages concerning low tritium retention and oxygen gettering were experimentally confirmed by global gas balance studies [6] and optical spectroscopy [7]. All these measurements confirm that Be is the main and dominant intrinsic impurity in limited and diverted plasmas with the JET-ILW.…”

Isotope exchange by Ion Cyclotron Wall Conditioning on JET

“…This contribution presents an overview of these experiments with focus on (i) ICWC discharge characterization both at ITER full field and half field scenario, (ii) investigating the accessible fuel reservoir by ICWC from particle balance analysis on JET-C and JET-ILW, as well as (iii) optimizing the fuel removal efficiency. Long-term fuel retention with JET-ILW was already shown to be at least ten times lower than in JET-C whereas the accessible reservoir near the surface, reflected in the short-term retention, is expected to be in the same range [5].…”

Quantitative modeling of fuel retention in the JET-C and JET-ILW wall configurations by WallDYN and predictions for ITER

“…According to [20] this is a reasonable assumption for JET-ILW. For JET-C this amounts to shots long after the last Be evaporation, as the ones used for gas balance measurements in [14].…”

“…Apart from temperature all the other parameters are readily available during a Wall-DYN calculation. The temperatures are taken from experiment (according to [14]) as follows: For the ohmic case (shot 80295) the entire wall is assumed to be at base temperature of 473K. For the H-mode case the outer limiters are at 550K, the outer strike point at 1400K, the inner strike point at 800K and the inner limiters at 600K.…”

“…From the calculated layer growth the co-deposition based retention rates were derived using the scaling laws from [7][8][9]. These retention rates are then compared to the results from gas balance measurements during JET-ILW and JET-C configurations taken from [14]. Applying the same model as for the JET calculations, the impurity migration and resulting fuel species co-deposition in ITER for different wall configurations and background plasmas was calculated.…”