The influence of an ITER-like wall on disruptions at JET

Vries, P. C. de; Baruzzo, M.; Hogeweij, G. M. D.; Jachmich, S.; Joffrin, E.; Lomas, P. J.; Matthews, G. F.; Murari, A.; Nunes, I.; Pütterich, T.; Reux, C.; Vega, J.; Contributors, Jet‐Efda

doi:10.1063/1.4872017

Cited by 66 publications

(72 citation statements)

References 25 publications

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“…Introduction: A study of the root causes of disruptions in the JET tokamak found that neoclassical tearing modes (NTMs) were the single most common cause [1,2]. Theoretical calculations in the early 1980's showed the feasibility of using rf current drive to stabilize tearing modes [3,4].…”

Section: Pacs Numbersmentioning

confidence: 99%

Suppression of Tearing Modes by Radio Frequency Current Condensation

Reiman

Fisch

2018

Phys. Rev. Lett.

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Currents driven by rf (radio frequency) waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization assume that the local electron acceleration is unaffected by the presence of the island. However, the power deposition and electron acceleration are sensitive to the perturbation of the temperature. The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and can lead to a bifurcation of the solution to the steady-state heat diffusion equation. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. The threshold for the effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER. PACS numbers:Introduction: A study of the root causes of disruptions in the JET tokamak found that neoclassical tearing modes (NTMs) were the single most common cause [1,2]. Theoretical calculations in the early 1980's showed the feasibility of using rf current drive to stabilize tearing modes [3,4]. The recognition in the late 1990's that bootstrap currents were driving NTMs in hot, collisionless tokamak plasmas [5][6][7][8], led to a resurgence of theoretical work in this area [9][10][11][12][13], to experimental demonstrations of stabilization [14][15][16][17][18][19][20], and to continuing intensive attention [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. A variety of rf waves are used to drive current [41], but, for stabilizing the NTM, the most studied methods are electron cyclotron current drive (ECCD) [42] and lower hybrid current drive (LHCD) [43]. ITER is designed with an NTM ECCD stabilization capability, with continued effort to model and improve this capability [25,29,30,44]. We identify here an rf current condensation effect, previously overlooked, which can significantly facilitate island stabilization.Calculations of rf stabilization of magnetic islands assume, at present, that the local acceleration of electrons is unaffected by the presence of the island. However, the local deposition is sensitive to small changes in the temperature, and these changes can be significantly affected by the presence of an island. The effect on the local deposition becomes significant when the fractional temperature perturbation exceeds about 5% for electron cyclotron waves and 2.5% for lower hybrid waves. Temperature perturbations as high as 20% have been measured in islands in rf stabilization experiments [45].In the conventional picture of rf current drive stabilization of a rotating island, a geometric effect associated with the equilibration of the rf driven current density within the flux surfaces of the island leads to a higher current density near the center of the island than near its peripher...

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Section: Pacs Numbersmentioning

confidence: 99%

Suppression of Tearing Modes by Radio Frequency Current Condensation

Reiman

Fisch

2018

Phys. Rev. Lett.

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“…NTMs were recognised as a source of major disruptions in experiments such as JET 6,7 , and thus their stabilisation is central. Amongst proposed stabilisation approaches, driving current 8,9 at the islands with RF waves has stimulated a long list of added efforts, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] including many experimental demonstrations [30][31][32][33][34][35][36] .…”

Section: Introductionmentioning

confidence: 99%

RF current condensation in magnetic islands and associated hysteresis phenomena

Reiman

Fisch

2019

Physics of Plasmas

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The nonlinear RF current condensation effect suggests that magnetic islands might be well controlled with broader deposition profiles than previously thought possible. To assess this possibility, a simplified energy deposition model in a symmetrised 1D slab geometry is constructed. By limiting the RF wave power that can be absorbed through damping, this model describes also the predicted hysteresis phenomena. Compared to the linear model, the nonlinear effects lead to larger temperature variations, narrower deposition widths, and more robust island stabilisation. Although, in certain regimes, the island centre can be disadvantageously shaded because of the nonlinear effects, in general, the RF condensation effect can take place, with current preferentially generated, advantageously, close to the island centre.

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“…If all of the latter events were to lead to the termination of the plasma, this would translate in a 0.8% TIE-induced plasma termination rate. This is a factor 4 lower than the unintentional disruption rate observed in the last years of JET-C (3.4%) and an order of magnitude lower than the rate observed in the 2011-2012 JET-ILW campaigns (10%) [6].…”

Section: Impact On Plasma Operation and Parametric Dependenciesmentioning

confidence: 96%

“…The limited amount of TIE-induced disruptions are not reported since they have been intensively analyzed elsewhere (see e.g. [6]). Modeling of the particle ablation has been performed using the dust code DTOKS [7].…”

Section: Introductionmentioning

confidence: 98%

Impact of W events and dust on JET-ILW operation

Sertoli

Flanagan

Bacharis

et al. 2015

Journal of Nuclear Materials

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a b s t r a c tThe occurrence of transient impurity events (TIE) leading to intense radiation spikes in JET plasma discharges has been studied since the installation of the ITER-like wall (ILW). To generate the observed average increase in radiated power of 1.5 MW, a spherical particle of solid W of radius >90 lm would be required. The drop in plasma energy caused by W-TIEs is fully recovered in 90% of all cases, only 1% inducing a longer term loss in plasma energy which sometimes leads to the shut-down of plasma operation. TIEs are correlated with disruptions and with measurements of the dust mobilized by disruptions using the high resolution Thomson scattering (HRTS) diagnostic. The dust characteristics giving rise to TIEs have been studied using the dust transport code DTOKS and the 1D impurity transport code STRAHL.

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The influence of an ITER-like wall on disruptions at JET

Cited by 66 publications

References 25 publications

Suppression of Tearing Modes by Radio Frequency Current Condensation

Suppression of Tearing Modes by Radio Frequency Current Condensation

RF current condensation in magnetic islands and associated hysteresis phenomena

Impact of W events and dust on JET-ILW operation

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