Control and dissipation of runaway electron beams created during rapid shutdown experiments in DIII-D

Hollmann, E. M.; Austin, M. E.; Boedo, J.A.; Brooks, N.H.; Commaux, N.; Eidietis, N. W.; Humphreys, D.A.; Izzo, V.A.; James, A.N.; Jernigan, T. C.; Loarte, A.; Martin-Solís, J.R.; Moyer, R. A.; Muñoz-Burgos, J. M.; Parks, P. B.; Rudakov, D.L.; Strait, E. J.; Tsui, C.; Zeeland, M. A. Van; Wesley, J.C.; Yu, J. H.

doi:10.1088/0029-5515/53/8/083004

Cited by 105 publications

(176 citation statements)

References 23 publications

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“…The synchrotron spectrum at each time step was calculated using SYRUP. In the calculations, the maximum particle energy was restricted to 22 MeV, in agreement with experimental observations [22]. (This maximum energy limit cannot be attributed to the effects of the synchrotron losses; other mechanisms, such as radial transport, must be invoked to explain it, but this is outside the scope of this Letter.)…”

Section: /2supporting

confidence: 80%

Effective Critical Electric Field for Runaway-Electron Generation

et al. 2015

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In this Letter we investigate factors that influence the effective critical electric field for runaway-electron generation in plasmas. We present numerical solutions of the kinetic equation and discuss the implications for the threshold electric field. We show that the effective electric field necessary for significant runaway-electron formation often is higher than previously calculated due to both (1) extremely strong dependence of primary generation on temperature, and (2) synchrotron radiation losses. We also address the effective critical field in the context of a transition from runaway growth to decay. We find agreement with recent experiments, but show that the observation of an elevated effective critical field can mainly be attributed to changes in the momentumspace distribution of runaways, and only to a lesser extent to a de facto change in the critical field.

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Section: /2supporting

confidence: 80%

Effective Critical Electric Field for Runaway-Electron Generation

et al. 2015

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“…2 (b)). These values of |dI p /dt| and I (RE) p are close to the ones observed in the similar experiments in the DIII-D tokamak (see, e.g., [15]). …”

supporting

confidence: 90%

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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“…(4) with DIII-D and ITER-like parameters. For DIII-D we set B 0 ¼ 2:19 T, R 0 ¼ 1:5 m, and minor radius r edge ¼ 0.5 m. Observations of RE disruptions in DIII-D 25 suggest that for these plasmas the safety factor at the plasma edge varies between q edge ¼ 2 and q edge ¼ 3. We consider these two values for q edge and choose q 0 so that q edge =q 0 ¼ 1:25 in both cases.…”

Section: Full Orbit Effects On Synchrotron Radiationmentioning

confidence: 99%

Space dependent, full orbit effects on runaway electron dynamics in tokamak plasmas

et al. 2017

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The dynamics of RE (runaway electrons) in fusion plasmas span a wide range of temporal scales, from the fast gyro-motion, ∼10−11 s, to the observational time scales, ∼10−2→1 s. To cope with this scale separation, RE are usually studied within the bounce-average or the guiding center approximations. Although these approximations have yielded valuable insights, a study with predictive capabilities of RE in fusion plasmas calls for the incorporation of full orbit effects in configuration space in the presence of three-dimensional magnetic fields. We present numerical results on this problem using the Kinetic Orbit Runaway electrons Code that follows relativistic electrons in general electric and magnetic fields under the full Lorentz force, collisions, and radiation losses. At relativistic energies, the main energy loss is due to radiation damping, which we incorporate using the Landau-Lifshitz formulation of the Abraham-Lorentz-Dirac force. The main focus is on full orbit effects on synchrotron radiation. It is shown that even in the absence of magnetic field stochasticty, neglecting orbit dynamics can introduce significant errors in the computation of the total radiated power and the synchrotron spectra. The statistics of collisionless (i.e., full orbit induced) pitch angle dispersion, and its key role played on synchrotron radiation, are studied in detail. Numerical results are also presented on the pitch angle dependence of the spatial confinement of RE and on full orbit effects on the competition of electric field acceleration and radiation damping. Finally, full orbit calculations are used to explore the limitations of gyro-averaging in the relativistic regime. To explore the practical impact of the results, DIII-D and ITER-like parameters are used in the simulations.

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Control and dissipation of runaway electron beams created during rapid shutdown experiments in DIII-D

Cited by 105 publications

References 23 publications

Effective Critical Electric Field for Runaway-Electron Generation

Effective Critical Electric Field for Runaway-Electron Generation

Mechanism of runaway electron beam formation during plasma disruptions in tokamaks

Space dependent, full orbit effects on runaway electron dynamics in tokamak plasmas

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