Dynamic fuel retention and release under ITER like wall conditions in JET

Abstract. This paper presents the DYON simulations of the plasma burn-through phase at Joint European Torus (JET) with the ITER-like wall. The main purpose of the study is to validate the simulations with the ITER-like wall, made of beryllium. Without impurities, the burn-through process of a pure deuterium plasma is described using DYON simulations, and the criterion for deuterium burn-through is derived analytically. The plasma burn-through with impurities are simulated using wallsputtering models in the DYON code, which are modified for the ITER-like wall. The wall-sputtering models and the validation against JET data are presented. The impact of the assumed plasma parameters in DYON simulations are discussed by means of parameter scans. As a result, the operation space of prefill gas pressure and toroidal electric field for plasma burn-through in JET is compared to the Townsend avalanche criterion.Physics of plasma burn-through and DYON simulations for the JET ITER-like wall 2

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“…Y D D = 0.9 → 1. This is consistent with the outgassing observed after discharges with the ITER-like wall [21].…”

Section: Physics Of Plasma Burn-through and Dyon Simulations For The supporting

confidence: 90%

Physics of plasma burn-through and DYON simulations for the JET ITER-like wall

Kim¹,

Sips²,

Contributors³

2013

Nucl. Fusion

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“…Co-deposition with W is not of importance and implantation is the main mechanism for the retention in W as experiments in ASDEX Upgrade confirmed [34], but it plays itself a negligible role in comparison with the Be co-deposition. Long-term outgassing also observed in JET-C, but being of minor importance due to the higher absolute retention [35], has also been observed in JETILWfor about 100h after plasma pulses with the deuterium pressure decaying according to ~t −0.8 [29] which will lead to a further substantial reduction of the fuel content in the metallic PFCs. Therefore it is expected that the post mortem analysis of Be andWcomponents will show a significant lower long term fuel content as deduced from the gas balances.…”

Section: Fuel Retentionmentioning

confidence: 67%

“…However, the outgassing after the discharge over compensates this transient retention [29]. The long term retention, i.e.…”

Section: Fuel Retentionmentioning

confidence: 99%

First operation with the JET International Thermonuclear Experimental Reactor-like wall

et al. 2013

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AbstrAct.To consolidate ITER design choices and prepare for its operation, JET has implemented ITER's plasma facing materials, namely Be at the main wall and W in the divertor. In addition, protection systems, diagnostics and the vertical stability control were upgraded and the heating capability of the neutral beams was increased to over 30 MW. First results confirm the expected benefits and the limitations of all metal plasma facing components (PFCs), but also yield understanding of operational issues directly relating to ITER. H-retention is lower by at least a factor of 10 in all operational scenarios compared to that with C PFCs. The lower C content (Section 1factor 10) have led to much lower radiation during the plasma burn-through phase eliminating breakdown failures.Similarly, the intrinsic radiation observed during disruptions is very low, leading to high power loads and to a slow current quench. Massive gas injection using a D 2 /Ar mixture restores levels of radiation and vessel forces similar to those of mitigated disruptions with the C wall. Dedicated L-H transition experiments indicate a reduced power threshold by 30%, a distinct minimum density and pronounced shape dependence. The L-mode density limit was found up to 30% higher than for C allowing stable detached divertor operation over a larger density range. Stable H-modes as well as the hybrid scenario could be only re-established when using gas puff levels of a few 10 21 es −1. On average the confinement is lower with the new PFCs, but nevertheless, H factors up to 1 (H-Mode) and 1.3 (at b N ≈ 3, hybrids) have been achieved withWconcentrationswell below themaximum acceptable level.

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“…Net fuel retention needs to be avoided in wall conditioning as it may be governed by permanent retention by codeposition in remote areas. As most of the isotopes are recovered in the post discharge phase (high outgassing pressure peak followed by a slow pressure decay [15]), duty cycle optimization studies for ICWC on JET-ILW still need further consideration. The accessible fuel reservoir by H 2 -ICWC on JET-ILW III preloaded by D 2 tokamak operation is estimated to be 7.3x10 22 hydrogenic atoms.…”

Section: Discussionmentioning

confidence: 99%

Isotope exchange by Ion Cyclotron Wall Conditioning on JET

Wauters¹,

Douai

Kogut

et al. 2015

Journal of Nuclear Materials

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The isotopic exchange efficiencies of JET Ion Cyclotron Wall Conditioning (ICWC) discharges produced at ITER half and full field conditions are compared for JET carbon (C) and ITER like wall (ILW). Besides an improved isotope exchange rate on the ILW providing cleaner plasma faster, the main advantage compared to C-wall is a reduction of the ratio of retained discharge gas to removed fuel. Complementing experimental data with discharge modeling shows that long pulses with high (~240kW coupled) ICRF power maximizes the wall isotope removal per ICWC pulse. In the pressure range 1 to 7.5 x10 -3 Pa, this removal reduces with increasing discharge pressure. As most of the wall-released isotopes are evacuated by vacuum pumps in the post discharge phase, duty cycle optimization studies for ICWC on JET-ILW need further consideration. The accessible reservoir by H 2 -ICWC at ITER half field conditions on the JET-ILW preloaded by D 2 tokamak operation is estimated to be 7.3 x10 22 hydrogenic atoms, and may be exchanged within 400s of cumulated ICWC discharge time.

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Dynamic fuel retention and release under ITER like wall conditions in JET

Cited by 45 publications

References 12 publications

Physics of plasma burn-through and DYON simulations for the JET ITER-like wall

Physics of plasma burn-through and DYON simulations for the JET ITER-like wall

First operation with the JET International Thermonuclear Experimental Reactor-like wall

Isotope exchange by Ion Cyclotron Wall Conditioning on JET

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