Avalanche runaway growth rate from a momentum-space orbit analysis

Parks, P. B.; Rosenbluth, M. N.; Putvinski, S.

doi:10.1063/1.873524

Cited by 47 publications

(55 citation statements)

References 15 publications

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“…The definition of ne,?. includes both free, ne, and bound electrons since both contribute to collisional drag of relativistic electrons [6]. RE experience amplification via the knock-on avalanche process in the current quench.…”

Section: Fig 7 Example Of Plasma/impurity Therrnal and Ionization-smentioning

confidence: 99%

Disruption mitigation with high-pressure noble gas injection

Whyte

Jernigan

Humphreys

et al. 2003

Journal of Nuclear Materials

123

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Section: Fig 7 Example Of Plasma/impurity Therrnal and Ionization-smentioning

confidence: 99%

Disruption mitigation with high-pressure noble gas injection

Whyte

Jernigan

Humphreys

et al. 2003

Journal of Nuclear Materials

123

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“…[28,29]), and (ii) an approximate secondary source is included which captures the effect of a finite energy incident electron population. This treatment accurately captures the analytical results of RE generation models [5,6,30] as well as the near-threshold regime [13]. The computed f e evolution is then placed through a forward model taking into account bremsstrahlung emission coefficients and sight-line geometry to obtain the predicted f γ [24].…”

mentioning

confidence: 99%

Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks

et al. 2017

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Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay of electric field acceleration with collisional and synchrotron damping. Measurements are consistent with theoretical predictions of momentum-space attractors that accumulate runaway electrons. RE distribution functions are measured to shift to a higher energy when the synchrotron force is reduced by decreasing the toroidal magnetic field strength. Increasing the collisional damping by increasing the electron density (at a fixed magnetic and electric field) reduces the energy of the nonmonotonic feature and reduces the HXR growth rate at all energies. Higher-energy HXR growth rates extrapolate to zero at the expected threshold electric field for RE sustainment, while low-energy REs are anomalously lost. The compilation of HXR emission from different sight lines into the plasma yields energy and pitch-angle-resolved RE distributions and demonstrates increasing pitch-angle and radial gradients with energy. DOI: 10.1103/PhysRevLett.118.255002 Introduction.-Reaching mega-ampere currents and mega-electron volt (MeV) energies during fast shutdown events, runaway electrons (REs) pose perhaps the greatest operational risk to tokamak fusion reactors such as ITER [1][2][3][4]. Because of the severe potential for damage to the reactor walls, opportunities for empirical tuning of RE control actuators will be limited. Instead, a first-principles predictive understanding is needed, and present-day experiments fill a crucial need in validating theoretical predictions of RE dissipation.Classical theories for relativistic RE generation in tokamaks based on the effects of Coulomb collisions (small angle [5] and secondary avalanche [6]) determine the critical electric field (E C ) for the growth of RE populations. Further work highlighted the important role of synchrotron damping in elevating the threshold electric field above E C [7,8], and several experiments have since yielded evidence of the elevated threshold [9][10][11][12]. These observations motivated the development of a rigorous analytical theory [13] and computational tools [14][15][16][17][18][19] that clarified the importance of the effects of pitch-angle scattering and synchrotron damping. Alongside quantifying the enhancement of the threshold field, these works predict phase-space circulation around an attractor resulting in a pileup of REs at specific energies potentially resulting in nonmonotonic features in the RE distribution function (f e ). While important to the RE dissipation rate and thus the prospects for control, neither

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“…14 The Chew-Goldberger-Low (CGL) theory, 15 also known as the double adiabatic theory, applies to such anisotropic plasma, provided that no coupling exists between the parallel and perpendicular degrees of freedom. 16 In such plasmas, one needs to separate the equations of state, i.e., to evaluate the ion pressure, viz., p k;i and p ? ;i , where p k;i and p ?…”

Section: Introductionmentioning

confidence: 99%

On the characteristics of obliquely propagating electrostatic structures in non-Maxwellian plasmas in the presence of ion pressure anisotropy

et al. 2017

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The dynamical characteristics of large amplitude ion-acoustic waves are investigated in a magnetized plasma comprising ions presenting space asymmetry in the equation of state and non-Maxwellian electrons. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low theory. An excess in the superthermal component of the electron population is assumed, in agreement with long-tailed (energetic electron) distribution observations in space plasmas; this is modeled via a kappa-type distribution function. Large electrostatic excitations are assumed to propagate in a direction oblique to the external magnetic field. In the linear (small amplitude) regime, two electrostatic modes are shown to exist. The properties of arbitrary amplitude (nonlinear) obliquely propagating ion-acoustic solitary excitations are thus investigated via a pseudomechanical energy balance analogy, by adopting a Sagdeev potential approach. The combined effect of the ion pressure anisotropy and excess superthermal electrons is shown to alter the parameter region where solitary waves can exist. An excess in the suprathermal particles is thus shown to be associated with solitary waves, which are narrower, faster, and of larger amplitude. Ion pressure anisotropy, on the other hand, affects the amplitude of the solitary waves, which become weaker (in strength), wider (in spatial extension), and thus slower in comparison with the cold ion case.

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Avalanche runaway growth rate from a momentum-space orbit analysis

Cited by 47 publications

References 15 publications

Disruption mitigation with high-pressure noble gas injection

Disruption mitigation with high-pressure noble gas injection

Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks

On the characteristics of obliquely propagating electrostatic structures in non-Maxwellian plasmas in the presence of ion pressure anisotropy

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