Speaker
Mr
Cristian Sommariva
(CEA-Cadaracher/IRFM)
Description
During a tokamak disruption, a large electric field is formed which can lead to the generation of a runaway electron (RE) beam. In large machines, runaway beams are sufficiently intense and energetic to represent a serious threat for operations. Therefore, the comprehension of the physics of RE and of their mitigation is of fundamental importance for future operations. Up to now, most RE modelling works have assumed axisymmetric MHD fields. This hypothesis is however clearly not valid during disruptions, which motivates our effort to investigate RE physics in 3D fields representative of disruptions.
For this purpose, a fast particle tracking module was developed within the non-linear MHD code JOREK [1]. The tracker computes relativistic particle trajectories using either a Full Orbit (FO) or a Guiding Center (GC) model in 3D time-varying MHD fields from JOREK. The module was successfully verified checking the conservation of the invariants of motion and the GC-FO agreement in a number of configurations.
In this work we investigate the possible primary RE generation mechanisms by simulating the behaviour of a test-particle population in JOREK - JET MGI-triggered disruption simulations [2][3] using the GC tracker. In order to become runaway, an electron has to remain confined throughout the Thermal Quench (TQ) and the electric field acceleration has to overcome the collisional drag. We quantify first the fraction of TQ survivors for a given electron energy, cutting acceleration terms in the equation of motion, making a link with local transport properties in the stochastic magnetic field. Secondly, we investigate the possibility of running away, restoring acceleration terms, in particular the parallel electric field and a drag force representative of collisional effects. Pointwise comparisons between the FO and the GC description are used to verify the GC model validity.
[1] C. Sommariva, to be submitted to NF, 2017
[2] A. Fil et al., Physics of Plasmas, vol. 22, pp. 062509, 2015
[3] E. Nardon et al., Plasma Phys. Control. Fusion, vol. 59, pp. 014006, 2016
Primary author
Mr
Cristian Sommariva
(CEA-Cadaracher/IRFM)
Co-authors
Mr
Daan van Vugt
(T.U. Eindhoven)
Dr
Eric Nardon
(CEA-Cadarache/IRFM)
Prof.
Guido Huijsmans
(CEA-Cadarache/IRFM and T.U. Eindhoven)
Dr
Matthias Hoelzl
(Max Planck institute for plasma physics Garching)
