Section: New Results

Physics

Physical studies

Parallel Kelvin-Helmholtz instability

Participants : Hervé Guillard, Marco Bilanceri, Céline Colin [CEA] , Philippe Ghendrih [CEA] , Giorgio Giorgiani, Boniface Nkonga, Frédéric Schwander [M2P2, AMU] , Eric Serre [M2P2, AMU] , Patrick Tamain [CEA] .

In the scrape-off layer (SOL) of tokamaks, the flow acceleration due to the presence of limiter or divertor plates rises the plasma velocity in a sonic regime. These high velocities imply the presence of a strong shear between the SOL and the core of the plasma that can possibly trigger some parallel shear flow instability. The existence of these instabilities, denoted as parallel Kelvin-Helmholtz instability in some works have been investigated theoretically in [51] using a minimal model of electrostatic turbulence composed of a mass density and parallel velocity equations. This work showed that the edge plasma around limiters might indeed be unstable to this type of parallel shear flow instabilities. In this work, begun in 2013, we have performed large scale 3D simulations using the PlaTo platform of the same simple mathematical model to investigate this question. The numerical results confirm that in agreement with the theoretical expectations as well as with other numerical methods, the sheared flows in the SOL are subject to parallel Kelvin-Helmholtz instabilities. However, the growth rate of these instabilities is low and these computations require both a sufficient spatial resolution and a long simulation time. This makes the simulation of parallel Kelvin-Helmholtz instabilities a demanding benchmark but it also allows us to validate the parallel implementation of the PlaTo platform up to up to $𝒪\left(1000\right)$ CPU [14] .