Since the ITER-like wall in JET (JET-ILW) came into operation, dedicated ITER-like plasma current (I-p) ramp-up (RU) and ramp-down (RD) experiments have been performed and matched to similar discharges with the carbon wall (JET-C). The experiments show that access to H-mode early in the I-p RU phase and maintaining H-mode in the I-p RD as long as possible are instrumental to achieve low internal plasma inductance (l(i)) and to minimize flux consumption. In JET-ILW, at a given current rise rate similar variations in l(i) (0.7-0.9) are obtained as in JET-C. In most discharges no strong W accumulation is observed. However, in some low density cases during the early phase of the I-p RU (n(e)/n(e)(Gw) similar to 0.2) strong core radiation due to W influx led to hollow electron temperature (T-e) profiles. In JET-ILW Z(eff) is significantly lower than in JET-C. W significantly disturbs the discharge evolution when the W concentration approaches 10(-4); this threshold is confirmed by predictive transport modelling using the CRONOS code. I-p RD experiments in JET-ILW confirm the result of JET-C that sustained H-mode and elongation reduction are both instrumental in controlling l(i).

ITER-like current ramps in JET with ILW: experiments, modelling and consequences for ITER

DE TOMMASI, GIANMARIA;
2015

Abstract

Since the ITER-like wall in JET (JET-ILW) came into operation, dedicated ITER-like plasma current (I-p) ramp-up (RU) and ramp-down (RD) experiments have been performed and matched to similar discharges with the carbon wall (JET-C). The experiments show that access to H-mode early in the I-p RU phase and maintaining H-mode in the I-p RD as long as possible are instrumental to achieve low internal plasma inductance (l(i)) and to minimize flux consumption. In JET-ILW, at a given current rise rate similar variations in l(i) (0.7-0.9) are obtained as in JET-C. In most discharges no strong W accumulation is observed. However, in some low density cases during the early phase of the I-p RU (n(e)/n(e)(Gw) similar to 0.2) strong core radiation due to W influx led to hollow electron temperature (T-e) profiles. In JET-ILW Z(eff) is significantly lower than in JET-C. W significantly disturbs the discharge evolution when the W concentration approaches 10(-4); this threshold is confirmed by predictive transport modelling using the CRONOS code. I-p RD experiments in JET-ILW confirm the result of JET-C that sustained H-mode and elongation reduction are both instrumental in controlling l(i).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/592310
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