Toroidal effect on runaway vortex and avalanche growth rate
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 taking into account, have 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 sec while the collisional time is of ~ 0.01 sec in ITER-like plasmas, a bounce-averaged formulation can drastically reduce computational cost. Here the LAPS-RFP 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.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC). Fusion Energy Sciences (FES) (SC-24)
- Grant/Contract Number:
- 89233218CNA000001
- OSTI ID:
- 1558965
- Report Number(s):
- LA-UR--18-28552
- Journal Information:
- Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 8 Vol. 26; ISSN 1070-664X
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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