Disruption mitigation by massive gas injection in JET

Lehnen, M.; Alonso, A.; Arnoux, G.; Baumgarten, N.; Bozhenkov, S.; Brezinsek, S.; Brix, M.; Eich, T.; Gerasimov, S.; Huber, A.; Jachmich, S.; Kruezi, U.; Morgan, P. D.; Plyusnin, Victor F.; Reux, C.; Riccardo, V.; Sergienko, G.; Stamp, M.; Contributors, Jet

doi:10.1088/0029-5515/51/12/123010

Cited by 172 publications

(186 citation statements)

References 28 publications

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“…The coupled energy is calculated from the current decay using a lumped parameter model for the mutual inductance, which includes energy flow to the vessel and the divertor coils [5,6]. For fast current quenches (CQ), the coupled energy amounts to 50% and to 30% for very long current decays.…”

Section: Fig 1: Comparison Of Two Disruptions With Cfc and Ilw Whicmentioning

confidence: 99%

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Impact and mitigation of disruptions with the ITER-like wall in JET

et al. 2013

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Abstract:Disruptions are a critical issue for ITER because of the high thermal and magnetic energies that are released on short time scales, which results in extreme forces and heat loads. The choice of material of the plasma facing components (PFCs) can have significant impact on the loads that arise during a disruption. With the ITER-like wall (ILW) in JET made of beryllium in the main chamber and tungsten in the divertor, the main finding is a low fraction of radiation. This has dropped significantly with the ILW from 50-100% of the total energy being dissipated in the plasma with CFC to less than 50% on average and down to just 10% for VDEs. All other changes in disruption properties and loads are consequences of this low radiation: long current quenches, high vessel forces caused by halo currents and toroidal current asymmetries as well as severe heat loads. Temperatures close to the melting limit have been locally observed on upper first wall structures during deliberate VDE and even at plasma currents as low as 1.5 MA and thermal energy of about 1.5 MJ only. A high radiation fraction can be regained by massive injection of a mixture of 10%Ar with 90%D 2 . This accelerates the current quench and by this reducing halo and sideways impact. The temperature of PFCs stays below 400 ∘ C. MGI is now a mandatory tool to mitigate disruptions in closed-loop operation for currents at and above 2.5 MA in JET.

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Section: Fig 1: Comparison Of Two Disruptions With Cfc and Ilw Whicmentioning

confidence: 99%

“…Massive gas injection is studied in JET as a tool for mitigation since 2008 [6]. With CFC wall, various gases have been used: argon, neon, mixtures of those with 90% D 2 and helium.…”

Section: Mitigation By Massive Gas Injectionmentioning

confidence: 99%

Impact and mitigation of disruptions with the ITER-like wall in JET

et al. 2013

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“…As an example of applications to 2-D configurations we consider experiments with massive gas injection into the tokamak JET to mitigate plasma disruptions [21,22]. Calculations have been performed for the conditions on the magnetic separatrix between the confined plasma region and the SOL, with R = 3m and r = 1m, the initial values of the electron temperature and density as in the shot 77808 with MGI into the H-mode plasma [22]: n 0 = 10 19 m −3 and T 0 = 250eV; the cooled area is a square with a side of 1m, i.e.…”

Section: 5∂mentioning

confidence: 99%

“…Calculations have been performed for the conditions on the magnetic separatrix between the confined plasma region and the SOL, with R = 3m and r = 1m, the initial values of the electron temperature and density as in the shot 77808 with MGI into the H-mode plasma [22]: n 0 = 10 19 m −3 and T 0 = 250eV; the cooled area is a square with a side of 1m, i.e. S c ≈ 0.01S s , where the density of argon atoms is increased instantaneously up to 2 × 10 24 m −3 .…”

Section: 5∂mentioning

confidence: 99%

Modelling of Global Heat Transfer by Local Cooling in Fusion Plasmas

Tokar¹

2015

Heat Transfer Studies and Applications

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“…[6][7][8] and references therein). However, no regular strategy to solve this problem has been developed because up to now the physical mechanisms of the formation of REs during plasma disruptions are not well understood.…”

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Mechanism of runaway electron beam formation during plasma disruptions in tokamaks

et al. 2015

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A new physical mechanism of formation of runaway electron (RE) beams during plasma disruptions in tokamaks is proposed. The plasma disruption is caused by a strong stochastic magnetic field formed due to nonlinearly excited low-mode number magnetohydrodynamic (MHD) modes. It is conjectured that the runaway electron beam is formed in the central plasma region confined inside the intact magnetic surface located between q = 1 and the closest low-order rational magnetic surfaces [q = 5/4 or q = 4/3, . . . ]. It results in that runaway electron beam current has a helical nature with a predominant m/n = 1/1 component. The thermal quench and current quench times are estimated using the collisional models for electron diffusion and ambipolar particle transport in a stochastic magnetic field, respectively. Possible mechanisms for the decay of the runaway electron current owing to an outward drift electron orbits and resonance interaction of high-energy electrons with the m/n = 1/1 MHD mode are discussed.The runaway electrons (REs) generated during the disruptions of tokamak plasmas may reach a several tens of MeV and may contribute to the significant part of postdisruption plasma current. The prevention of such RE beams is of a paramount importance in future tokamaks, especially in the ITER operation, since it may severely damage a device wall [1][2][3][4][5].The mitigation of REs by massive gas injections (MGI) and externally applied resonant magnetic perturbations (RMPs) have been extensively discussed in literature (see, e.g., Refs. [6-8] and references therein). However, no regular strategy to solve this problem has been developed because up to now the physical mechanisms of the formation of REs during plasma disruptions are not well understood. In spite of the numerous dedicated experiments to study the problem of runaway current generation during plasma disruptions in different tokamaks (see, e.g., [7][8][9][10][11][12][13][14][15]) no clear dependence of RE formation on plasma parameters has been established. These numerous experiments show the complex nature of plasma disruption process especially the formation of RE beams.One of the important features of the formation of RE beams is the irregularity and variability of the beam parameters from one discharge to another one. This is an indication of the sensitivity of RE beam formations on initial conditions which is the characteristic feature of nonlinear processes, particularly, the chaotic system. Therefore one expects that ab initio numerical simulations of the RE formation process may not be quite productive to explain it because of complexity of computer simulations of nonlinear processes [16]. The problems of numerical simulations of plasma disruptions is comprehensively discussed in [17].In this work we propose a new physical mechanism of formation of RE beams during plasma disruptions in tokamaks. It is based on the analysis of numerous experimental results, mainly obtained in the TEXTOR tokamak and the ideas of magnetic field stochasticity [18]. The mecha...

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Disruption mitigation by massive gas injection in JET

Cited by 172 publications

References 28 publications

Impact and mitigation of disruptions with the ITER-like wall in JET

Impact and mitigation of disruptions with the ITER-like wall in JET

Modelling of Global Heat Transfer by Local Cooling in Fusion Plasmas

Mechanism of runaway electron beam formation during plasma disruptions in tokamaks

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