Speaker
José Ángel Mier
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1054.pdf
A RELATIVISTIC LANGEVIN APPROACH FOR
RUNAWAY ELECTRONS IN TOKAMAK PLASMAS*
J. A. Mier1 , J. R. Martı́n-Solı́s2 and R. Sánchez2
1
Universidad de Cantabria, Avda. de los Castros s/n, Santander, 39005-Cantabria, Spain
2
Universidad Carlos III de Madrid, Avda. de la Universidad 30, Leganés, 28911-Madrid, Spain
ABSTRACT
The Langevin approach to the kinetics of a collisional plasma is developed for relativistic
electrons such as runaway electrons (RE) in tokamak plasmas. In this work, we consider
Coulomb collisions between very fast, relativistic electrons and a relatively cool, thermal
background plasma. The model is developed using the stochastic equivalence of the
Fokker-Planck and Langevin equations [1].
The resulting Langevin model equation for relativistic electrons is an stochastic differen-
tial equation (SDE), amenable to numerical simulations by means of Monte-Carlo type
codes. The approach will be used to analyze the two-dimensional runaway electron dy-
namics in momentum space (runaway probability and conditions for runaway, runaway
distribution function and generation rate) and the results of the simulations will be com-
pared with those from the non-relativistic Langevin equation for runaway electrons used
in the past [2].
Synchrotron radiation losses will be also included which: (1) increase the critical (mini-
mum) electric field for runaway generation; (2) set a limit on the maximum energy that
the runaways can reach. The resulting critical field and runaway limiting energy are
found to be in agreement with the values provided by a test particle description of the
runaway dynamics [3].
[1] V. I. Tikhonov and M. A. Mironov, Markovian Processes (1977). Soviet Radio,
Moscow.
[2] I. Fernández-Gómez, J. R. Martı́n-Solı́s and R. Sánchez, Phys. Plasmas 19 (2012)
102504.
[3] J. R. Martı́n-Solı́s, J. D. Álvarez, R. Sánchez and B. Esposito, Phys. Plasmas 5, 2370
(1998).
* This work was carried out with financial support from Dirección General de Investigación,
Cientı́fica y Técnica, Project No. ENE2015-65444-R (MINECO-FEDER, UE).
