Runaway electron losses caused by resonant magnetic perturbations in ITER

Based on the analysis of data from the numerous dedicated experiments on plasma disruptions in the TEXTOR tokamak the mechanisms of the formation of runaway electron beams and their losses are proposed. The plasma disruption is caused by strong stochastic magnetic field formed due to nonlinearly excited low-mode number magnetohydro-dynamics (MHD) modes. It is hypothesized that the runaway electron beam is formed in the central plasma region confined by an intact magnetic surface due to the acceleration of electrons by the inductive toroidal electric field. In the case of plasmas with the safety factor q(0) < 1 the most stable runaway electron beams are formed by the intact magnetic surface located between the magnetic surface q = 1 and the closest loworder rational surface q = m/n > 1 ( q = 5/4, q = 4/3, . . . ). The thermal quench time caused by the fast electron transport in a stochastic magnetic field is calculated using the collisional transport model. The current quench stage is due to the particle transport in a stochastic magnetic field. The runaway electron beam current is modeled as a sum of toroidally symmetric part and a small amplitude helical current with a predominant m/n = 1/1 component. The runaway electrons are lost due to two effects: (i) by outward drift of electrons in a toroidal electric field until they touch wall and (ii) by the formation of stochastic layer of runaway electrons at the beam edge. Such a stochastic layer for high-energy runaway electrons is formed in the presence of the m/n = 1/1 MHD mode. It has a mixed topological structure with a stochastic region open to wall. The effect of external resonant magnetic perturbations on runaway electron loss is discussed. A possible cause of the sudden MHD signals accompanied by runaway electron bursts is explained by the redistribution of runaway current during the resonant interaction of high-energetic electron orbits with the m/n = 1/1 MHD mode.

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“…2010 and Papp et al. 2011, 2012). However, up to now there is no regular strategy to solve this problem.…”

Section: Introductionmentioning

confidence: 93%

Mechanisms of plasma disruption and runaway electron losses in the TEXTOR tokamak

et al. 2015

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“…2007; Papp et al. 2011 a , b , 2012). The individual particle orbits in perturbed magnetic fields are chaotic (Papp et al.…”

Section: Introductionmentioning

confidence: 99%

Energetic electron transport in the presence of magnetic perturbations in magnetically confined plasmas

et al. 2015

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The transport of energetic electrons is sensitive to magnetic perturbations. By using three-dimensional numerical simulation of test particle drift orbits we show that the transport of untrapped electrons through an open region with magnetic perturbations cannot be described by a diffusive process. Based on our test particle simulations, we propose a model that leads to an exponential loss of particles.

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“…[17][18][19][20][21] The resonant magnetic perturbation is also considered to be of fundamental importance for the ITER tokamak advanced scenario. 3,11,22,23 Resonant magnetic perturbations are used, e.g., for the control of ELMs, the stabilization of detached plasmas, the suppression of high-energy electrons, and the control of tearing mode rotation. The latter two are of particular importance in RFP devices when the configuration evolves from 2D (toroidally axisymmetric) to 3D (helical, stellarator like).…”

Section: Introductionmentioning

confidence: 99%

Effect of resonant magnetic perturbations on three dimensional equilibria in the Madison Symmetric Torus reversed-field pinch

et al. 2016

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The orientation of 3D equilibria in the Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch can now be controlled with a resonant magnetic perturbation (RMP). Absent the RMP, the orientation of the stationary 3D equilibrium varies from shot to shot in a semi-random manner, making its diagnosis difficult. Produced with a poloidal array of saddle coils at the vertical insulated cut in MST's thick conducting shell, an m ¼ 1 RMP with an amplitude b r /B $ 10% forces the 3D structure into any desired orientation relative to MST's diagnostics. This control has led to improved diagnosis, revealing enhancements in both the central electron temperature and density. With sufficient amplitude, the RMP also inhibits the generation of high-energy (>20 keV) electrons, which otherwise emerge due to a reduction in magnetic stochasticity in the core. Field line tracing reveals that the RMP reintroduces stochasticity to the core. A m ¼ 3 RMP of similar amplitude has little effect on the magnetic topology or the high-energy electrons. V

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Runaway electron losses caused by resonant magnetic perturbations in ITER

Cited by 56 publications

References 23 publications

Mechanisms of plasma disruption and runaway electron losses in the TEXTOR tokamak

Mechanisms of plasma disruption and runaway electron losses in the TEXTOR tokamak

Energetic electron transport in the presence of magnetic perturbations in magnetically confined plasmas

Effect of resonant magnetic perturbations on three dimensional equilibria in the Madison Symmetric Torus reversed-field pinch

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