Characterisation of local ICRF heat loads on the JET ILW

Jacquet, P.; Marcotte, Frédérick; Colas, L.; Arnoux, G.; Bobkov, V.; Corre, Y.; Devaux, S.; Gardarein, J. L.; Gauthier, E.; Graham, M.; Lerche, E.; Mayoral, M.‐L.; Monakhov, I.; Rimini, F.; Sirinelli, A.; Eester, D. Van

doi:10.1016/j.jnucmat.2013.01.075

Cited by 18 publications

(22 citation statements)

References 20 publications

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“…The recent JET experimental campaign showed that for all currently attained ICRH power levels (P ICRH ≤ 4.5MW ), phasings and plasma configurations tested, the ILW and ICRH heating are compatible in L-mode as heat loads and impurity levels stay within acceptable limits without compromising the heating performance (see [1][2][3][4][5][6] for more details). Along with a strong reduction in the W level observed when the edge density is increased, it is found that it is beneficial to work at minority concentration of X[H] ≈ 15% -somewhat higher X[H] than those traditionally used for minority heating -to reduce the W concentration and bulk radiation.…”

Section: Final Remarksmentioning

confidence: 99%

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Effect of the minority concentration on ion cyclotron resonance heating in presence of the ITER-like wall in JET

Eester¹,

Lerche²,

Jacquet

et al. 2014

AIP Conference Proceedings

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The most recent JET campaign has focused on characterizing operation with the "ITER-like" wall. One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptably high levels of impurity influx, preventing fusion-relevant operation. In view of its high single pass absorption, hydrogen minority fundamental cyclotron heating in a deuterium plasma was chosen as the reference wave heating scheme in the ion cyclotron domain of frequencies. The present paper discusses the plasma behavior as a function of the minority concentration X [H] in L-mode with up to 4MW of RF power. It was found that the tungsten concentration decreases by a factor of 4 when the minority concentration is increased from X[H] approximate to 5% to X[H] approximate to 20% and that it remains at a similar level when X[H] is further increased to 30%; a monotonic decrease in Beryllium emission is simultaneously observed. The radiated power drops by a factor of 2 and reaches a minimum at X [H] approximate to 20%. It is discussed that poor single pass absorption at too high minority concentrations ultimately tailors the avoidance of the RF induced impurity influx. The edge density being different for different minority concentrations, it is argued that the impact ICRH has on the fate of heavy ions is not only a result of core (wave and transport) physics but also of edge dynamics and fueling

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Section: Final Remarksmentioning

confidence: 99%

“…This paper briefly reports on two related aspects of the present understanding of ion cyclotron resonance heating (ICRH) or radio frequency (RF) heating in presence of the ILW: ICRH-specific impurity influx and heating performance. Complementing related discussions can be found in [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Effect of the minority concentration on ion cyclotron resonance heating in presence of the ITER-like wall in JET

Eester¹,

Lerche²,

Jacquet

et al. 2014

AIP Conference Proceedings

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“…A more detailed analysis revealed that the main chamber W components and the divertor apron tiles (Wcoated tiles covering the entrance of the divertor) rather than the main part of the divertor (bulk W) are the major source of impurities during high power ICRH, as reported by Bobkov et al [15]. The overall effect of the ILW metallic environment on ICRF heating in JET, including a detailed assessment of the RF-induced heat loads in plasma-facing components, are reported by Jacquet et al in [16,17]. The main conclusions are that the higher impurity content w.r.t.…”

Section: Introductionmentioning

confidence: 97%

“…The focus is on the RF heating efficiency and on the fast-particle physics (that controls the RF power eventually absorbed by the bulk plasma by collisions with the fast minority ions) since a detailed analysis of the plasma-wall interactions and the RF-induced impurity content comprising their dependence on the minority H concentration is already given in [15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Impact of minority concentration on fundamental (H)D ICRF heating performance in JET-ILW

Lerche

Eester²,

Jacquet

et al. 2014

Nucl. Fusion

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ITER will start its operation with non-activated hydrogen and helium plasmas at a reduced magnetic field of B 0 = 2.65 T. In hydrogen plasmas, the two ion cyclotron resonance frequency (ICRF) heating schemes available for central plasma heating (fundamental H majority and 2nd harmonic 3 He minority ICRF heating) are likely to suffer from relatively low RF wave absorption, as suggested by numerical modelling and confirmed by previous JET experiments conducted in conditions similar to those expected in ITER's initial phase. With 4 He plasmas, the commonly adopted fundamental H minority heating scheme will be used and its performance is expected to be much better. However, one important question that remains to be answered is whether increased levels of hydrogen (due to e.g. H pellet injection) jeopardize the high performance usually observed with this heating scheme, in particular in a full-metal environment. Recent JET experiments performed with the ITER-like wall shed some light onto this question and the main results concerning ICRF heating performance in L-mode discharges are summarized here.

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“…[11] The experimental results from JET indicate between 2-10% of the injected power is found on the antenna limiters and septum. [12] Tore Supra has also made extensive measurements and have shown that 3.5% of the injected power is found locally on the antenna. [13] To maintain coupled power to the plasma, an ICRF antenna needs to be load tolerant either intrinsically or through external matching.…”

Section: Introductionmentioning

confidence: 99%

Assessment of a field-aligned ICRF antenna

Wukitch¹,

Brunner²,

Ennever³

et al. 2014

AIP Conference Proceedings

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Abstract. Impurity contamination and localized heat loads associated with ion cyclotron range of frequency (ICRF) antenna operation are among the most challenging issues for ICRF utilization.. Another challenge is maintaining maximum coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. Here, we report on an experimental assessment of a field aligned (FA) antenna with respect to impurity contamination, impurity sources, RF enhanced heat flux and load tolerance. In addition, we compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to and the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E|| (electric field along a magnetic field line) via symmetry. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20-30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. Further we observe that the fraction of RF energy deposited upon the antenna is less than 0.4 % of the total injected RF energy in dipole phasing. The total deposited energy increases significantly when the FA antenna is operated in monopole phasing. The FA antenna also exhibits an unexpected load tolerance for ELMs and confinement transitions compared to the TA antennas. However, inconsistent with expectations, we observe RF induced plasma potentials to be nearly identical for FA and TA antennas when operated in dipole phasing. In monopole phasing, the FA antenna has the highest plasma potentials and poor heating efficiency despite calculations indicating low integrated E||. In mode conversion heating scenario, no core waves were detected in the plasma core indicating poor wave penetration. For monopole phasing, simulations suggest the antenna spectrum is peaked at very short wavelength and full wave simulations show the short wavelength has poor wave penetration to the plasma core.

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Characterisation of local ICRF heat loads on the JET ILW

Cited by 18 publications

References 20 publications

Effect of the minority concentration on ion cyclotron resonance heating in presence of the ITER-like wall in JET

Effect of the minority concentration on ion cyclotron resonance heating in presence of the ITER-like wall in JET

Impact of minority concentration on fundamental (H)D ICRF heating performance in JET-ILW

Assessment of a field-aligned ICRF antenna

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