Integration of a radiative divertor for heat load control into JET high triangularity ELMy H-mode plasmas

Giroud, C.; Maddison, G.; McCormick, K.; Beurskens, M.; Brezinsek, S.; Devaux, S.; Eich, T.; Frassinetti, L.; Fundamenski, W.; Groth, M.; Huber, A.; Jachmich, S.; Järvinen, A.; Kallenbach, A.; Krieger, K.; Moulton, D.; Saarelma, S.; Thomsen, H.; Wiesen, S.; Alonso, A.; Alper, B.; Arnoux, G.; Belo, P.; Boboc, A.; Brett, A.; Brix, M.; Coffey, I.; Luna, E. de la; Dodt, D.; Vries, P. de; Felton, R.; Giovanozzi, E.; Harling, J.; Harting, D.; Hawkes, N.; Hobirk, J.; Jenkins, I.; Joffrin, E.; Kempenaars, M.; Lehnen, M.; Loarer, T.; Lomas, P. J.; Mailloux, J.; McDonald, D. C.; Meigs, A.; Morgan, P. D.; Nunes, I.; Thun, C. Perez van; Riccardo, V.; Rimini, F.; Sirinnelli, A.; Stamp, M.; Voitsekhovitch, I.; Contributors, Jet

doi:10.1088/0029-5515/52/6/063022

Cited by 61 publications

(99 citation statements)

References 56 publications

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“…In the JET-C phase the use of nitrogen seeding was associated with a loss of energy confinement [50]. With JET-ILW however, nitrogen seeding raises the pedestal density and temperature, Fig.…”

Section: High Triangularity Inductive Scenario and Nitrogen Seedingmentioning

confidence: 99%

Plasma operation with an all metal first-wall: Comparison of an ITER-like wall with a carbon wall in JET

Matthews

Contributors

2013

Journal of Nuclear Materials

153

108

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Section: High Triangularity Inductive Scenario and Nitrogen Seedingmentioning

confidence: 99%

Plasma operation with an all metal first-wall: Comparison of an ITER-like wall with a carbon wall in JET

Matthews

Contributors

2013

Journal of Nuclear Materials

153

108

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“…A D 2 fuelling scan from  D ~ 0.2 to 6.1x10 22 electrons per second (el/s) was performed over 14 single null, Type I ELMy H-mode plasmas as described in [32,33]. The high triangularity plasma scenarios for the 2002 and present study are compared in Table 1.…”

Section: Plasma Scenariosmentioning

confidence: 99%

“…Also as shown by the arrow on Figure 1c the variation in D 2 fuelling from 0.2 to 6.1x10 22 el/s is provided by a gas injection model located at the inner divertor [32].…”

Section: Plasma Scenariosmentioning

confidence: 99%

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Leyland¹,

Beurskens²,

Frassinetti³

et al. 2013

Nucl. Fusion

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We present the results from a new fuelling scan database consisting of 14 high triangularity ( ~ 0.41), Type I ELMy H-mode JET plasmas. As the fuelling level is increased from low, ( D ~ 0.2x10 22 el/s, n e,ped /n gw =0.7), to high dosing ( D ~ 2.6x10 22 el/s, n e,ped /n gw =1.0) the variation in ELM behaviour is consistent with a transition from 'pure Type I' to 'mixed Type I/II' ELMs [1]. However, the pulses in Scattering (HRTS) system. We continue by presenting, for the first time, the role of pedestal structure, as quantified by a least squares mtanh fit to the HRTS profiles, on the performance across the fuelling scan. A key result is that the pedestal width narrows and peak pressure gradient increases during the ELM cycle for low fuelling plasmas, whereas at high fuelling the pedestal width and peak pressure gradient saturates towards the latter half of the ELM cycle. An ideal MHD stability analysis shows that both low and high fuelling plasmas move from stable to unstable approaching the ideal ballooning limit of the finite peeling ballooning stability boundary. Comparison to EPED predictions show on average good agreement with experimental measurements for both pedestal height and width however when presented as a function of pedestal density, experiment and model show opposing trends. The measured pre-ELM pressure pedestal height increases by ~ 20% whereas EPED predicts a decrease of 25% from low to high fuelling. Similarly the measured pressure pedestal width widens by ~ 55%, in poloidal flux space, whereas EPED predicts a decrease of 20% from low to high fuelling. We give two possible explanations for the disagreement. First, it may be that EPED under-predicts the critical density, which marks the transition from kink-peeling to ballooning limited plasmas. Second, the stronger broadening of the experimental pedestal width than predicted by EPED is an indication that other transport related processes contribute to defining the pedestal width such as enhanced inter-ELM transport as observed at high fuelling, for mixed Type I/II ELMy pulses.M. Leyland

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“…As in these predecessors, the goal is thus to span variations wide enough to be able to interpolate, rather than trying to extrapolate, to optimum conditions. Attention has been focused first on Type I ELMy H-mode, as the scenario foreseen for "baseline" inductive plasmas in ITER [11,12] , and initially on nitrogen as the seed impurity owing to its suitability as a radiator at typical JET divertor temperatures [73] , which favours a trend towards higher divertor over main-plasma emission, as seen in the all-C cases [44] .…”

Section: Introductionmentioning

confidence: 99%

“…Eventually this can develop into the detached regime, where volumetric losses dominate over then suppress plasma fluxes to the targets [75] , ostensibly defining an ideal power exhaust scheme for ITER [12] or DEMO [14] . Combination with extrinsic impurities remains necessary, however, since a pure fuelling approach to detachment at high power levels has too adverse an effect on global confinement [44,75] , so that as hinted above an optimum balance, and even possible synergy [24] , between the two inputs is required to obtain the best reconciliation of tolerable divertor loads with plasma performance. Importantly it was also found in all-C JET studies that energy confinement rises with higher magnetic shaping [76,77] and most notably that its robustness to increasing fuelling was much improved above a certain degree of triangularity, giving access to a new well-confined, high-density regime of lower ELM frequency and enhanced inter-ELM effluxes [77][78][79] .…”

Section: Introductionmentioning

confidence: 99%

Contrasting H-mode behaviour with deuterium fuelling and nitrogen seeding in the all-carbon and metallic versions of JET

et al. 2014

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The former all-carbon wall on JET has been replaced with beryllium in the main torus and tungsten in the divertor to mimic the surface materials envisaged for ITER. Comparisons are presented between Type I H-mode characteristics in each design by examining respective scans over deuterium fuelling and impurity seeding, required to ameliorate exhaust loads both in JET at full capability and in ITER. Attention is focused upon a common high-triangularity, single-null divertor configuration at 2.5 MA, q 95 ≈ 3.5 yielding the most robust all-C performance. Contrasting results between the alternative linings are found firstly in unseeded plasmas, for which purity is improved and intrinsic radiation reduced in the ITER-like wall (ILW) but normalised energy confinement is ≈ 30% lower than in all-C counterparts, owing to a commensurately lower (electron) pedestal temperature. Divertor recycling is also radically altered, with slower, inboard-outboard asymmetric transients at ELMs and spontaneous oscillations in between them. Secondly, nitrogen seeding elicits opposite responses in the ILW to all-C experience, tending to raise plasma density, reduce ELM frequency, and above all to recover (electron) pedestal pressure, hence global confinement, almost back to previous levels. A hitherto unrecognised role of light impurities in pedestal stability and dynamics is consequently suggested. Thirdly, while heat loads on the divertor outboard target between ELMs are successfully reduced in proportion to the radiative cooling and ELM recurrence effects of N in both wall environments, more surprisingly, average power ejected by ELMs and estimated scrape-off-layer pressure ratio during the approach to outboard detachment also both decline in the same proportion for the ILW. Finally, inter-ELM W sources in the ILW divertor tend to fall with N input, although core accumulation possibly due to net ELM erosion still leads to significantly less steady conditions than in all-C plasmas. This limitation of ILW H-modes so far will be readdressed in future campaigns to continue progress towards a fully-integrated scenario suitable for D-T experiments on JET and for "baseline" operation on ITER. The diverse changes in behaviour between all-C and ILW contexts demonstrate essentially the strong impact which boundary conditions and intrinsic impurities can have on tokamak-plasma states. ‡ That is, contours are interpolated between the torus-pressure values for each all-C and ILW shot at its position in the normalised confinement versus density plane.

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Integration of a radiative divertor for heat load control into JET high triangularity ELMy H-mode plasmas

Cited by 61 publications

References 56 publications

Plasma operation with an all metal first-wall: Comparison of an ITER-like wall with a carbon wall in JET

Plasma operation with an all metal first-wall: Comparison of an ITER-like wall with a carbon wall in JET

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Contrasting H-mode behaviour with deuterium fuelling and nitrogen seeding in the all-carbon and metallic versions of JET

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