Toroidal effect on runaway vortex and avalanche growth rate
Abstract
The momentum-space dynamics of runaway electrons in a slab geometry, in terms of both the geometry and topological transition of the runaway vortex when synchrotron radiative damping is taken into account, has recently been shown to play a crucial role in runaway mitigation and avoidance. In a tokamak geometry, magnetic trapping arises from parallel motion along the magnetic field that scales as 1/R in strength with R the major radius. Since the transit time for a runaway electron moving along the field is of order 10−8 s while the collisional time is of ∼0.01 s in ITER-like plasmas, a bounce-averaged formulation can drastically reduce computational cost. Here, the Los Alamos Plasma Simulation – Relativistic Fokker-Planck Solver code's implementation of a bounce-averaged relativistic Fokker-Planck model, along with the essential physics of synchrotron radiation damping and knock-on collisions, is described. It is found that the magnetic trapping can reduce the volume of the runaway vortex as the momentum-space fluxes are strongly modified inside the trapped-region. As a result, the avalanche growth rate is reduced at off-axis locations. In addition to benchmarking with previous calculations that did not take into account radiation damping, we also clarify how synchrotron radiation damping modifies the avalanche growth ratemore »
- Publication Date:
- Research Org.:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC). Fusion Energy Sciences (FES) (SC-24); USDOE
- OSTI Identifier:
- 1558965
- Alternate Identifier(s):
- OSTI ID: 1549543
- Report Number(s):
- LA-UR-18-28552
Journal ID: ISSN 1070-664X; TRN: US2000264
- Grant/Contract Number:
- 89233218CNA000001
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Physics of Plasmas
- Additional Journal Information:
- Journal Volume: 26; Journal Issue: 8; Journal ID: ISSN 1070-664X
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Magnetic Fusion Energy
Citation Formats
Guo, Zehua, Mcdevitt, Chris, and Tang, Xianzhu. Toroidal effect on runaway vortex and avalanche growth rate. United States: N. p., 2019.
Web. doi:10.1063/1.5055874.
Guo, Zehua, Mcdevitt, Chris, & Tang, Xianzhu. Toroidal effect on runaway vortex and avalanche growth rate. United States. https://doi.org/10.1063/1.5055874
Guo, Zehua, Mcdevitt, Chris, and Tang, Xianzhu. Fri .
"Toroidal effect on runaway vortex and avalanche growth rate". United States. https://doi.org/10.1063/1.5055874. https://www.osti.gov/servlets/purl/1558965.
@article{osti_1558965,
title = {Toroidal effect on runaway vortex and avalanche growth rate},
author = {Guo, Zehua and Mcdevitt, Chris and Tang, Xianzhu},
abstractNote = {The momentum-space dynamics of runaway electrons in a slab geometry, in terms of both the geometry and topological transition of the runaway vortex when synchrotron radiative damping is taken into account, has recently been shown to play a crucial role in runaway mitigation and avoidance. In a tokamak geometry, magnetic trapping arises from parallel motion along the magnetic field that scales as 1/R in strength with R the major radius. Since the transit time for a runaway electron moving along the field is of order 10−8 s while the collisional time is of ∼0.01 s in ITER-like plasmas, a bounce-averaged formulation can drastically reduce computational cost. Here, the Los Alamos Plasma Simulation – Relativistic Fokker-Planck Solver code's implementation of a bounce-averaged relativistic Fokker-Planck model, along with the essential physics of synchrotron radiation damping and knock-on collisions, is described. It is found that the magnetic trapping can reduce the volume of the runaway vortex as the momentum-space fluxes are strongly modified inside the trapped-region. As a result, the avalanche growth rate is reduced at off-axis locations. In addition to benchmarking with previous calculations that did not take into account radiation damping, we also clarify how synchrotron radiation damping modifies the avalanche growth rate in a tokamak.},
doi = {10.1063/1.5055874},
journal = {Physics of Plasmas},
number = 8,
volume = 26,
place = {United States},
year = {Fri Aug 09 00:00:00 EDT 2019},
month = {Fri Aug 09 00:00:00 EDT 2019}
}
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FIG. 1: The formation of a runaway vortex in momentum space for primary runaways depends on a threshold parallel electric field EOX. In all these diagrams, the horizontal axis is the kinetic energy of the relativistic electrons (normalized against mec 2) with γ the Lorentz factor, and the vertical axismore »
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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.