An advection-diffusion model for cross-field runaway electron transport in perturbed magnetic fields

TL;DR

This paper introduces an advection-diffusion model to better simulate runaway electron transport across magnetic fields in disrupted plasmas, addressing limitations of previous orbit-averaged models by incorporating stochastic magnetic effects.

Contribution

The paper develops a novel advection-diffusion model that couples orbit-following and orbit-averaged codes, accurately capturing cross-field transport influenced by magnetic stochasticity.

Findings

Diffusion coefficient significantly differs from Rechester-Rosenbluth result

Including advection models transport barriers and enhances loss predictions

Transport coefficients evaluated via Monte Carlo methods

Abstract

Disruption-generated runaway electrons (RE) present an outstanding issue for ITER. The predictive computational studies of RE generation rely on orbit-averaged computations and, as such, they lack the effects from the magnetic field stochasticity. Since stochasiticity is naturally present in post-disruption plasma, and externally induced stochastization offers a prominent mechanism to mitigate RE avalanche, we present an advection-diffusion model that can be used to couple an orbit-following code to an orbit-averaged tool in order to capture the cross-field transport and to overcome the latter's limitation. The transport coefficients are evaluated via a Monte Carlo method. We show that the diffusion coefficient differs significantly from the well-known Rechester-Rosenbluth result. We also demonstrate the importance of including the advection: it has a two-fold role both in modelling transport barriers created by magnetic islands and in amplifying losses in regions where the islands are not present.