Dust remobilization from rough planar surfaces in tokamak steady-state plasmas

A Autricque,S Peillon,F Gensdarmes,M Sow,N Fedorczak,H Roche,O Pluchery,C Grisolia

doi:10.1016/j.nme.2018.11.013

Abstract

The ability of tungsten (W) dust to be remobilized from rough tokamak plasma-facing surfaces is investigated in this study. Atomic Force Microscopy is used to evaluate the adhesion force distribution between W spheroids of ∼1−10 µm radius and a rough W substrate. Our results confirm that the Rabinovich model describes reasonably well the mean adhesion force in tokamak-relevant surface roughness regimes. The external (electric and ion drag) forces are estimated as well using a simplified sheath model. The results reveal that micron-size dust can be resuspended by attainable electric fields in tokamak conditions.

Highlights

Dust sources could play an important role in the impurity balance of fusion plasmas [1]
The mean is fitted using the Rabinovich model [33], which is based on the van der Waals force and incorporates the contribution of two surface roughness scales, characterized by their root mean square roughness rms1 and rms2 as well as the peak-to-peak distances λ1 and λ2
Electric fields applied on dust grains deposited onto planar surfaces can lead to remobilization under particular tokamak conditions

Summary

Introduction

Dust sources could play an important role in the impurity balance of fusion plasmas [1]. Works mentioned above do not account for the fact that adhesion forces are log-normally distributed [10] This means that dust remobilization is not a threshold process, but must be assessed in terms of resuspension probability. In accordance with the low surface roughness used in these measurements, the adhesion forces obtained were close to that of a spherical particle on a perfectly planar surface, given by the classical van der Waals expression [30], i.e., in the μN range for the particle sizes considered These values of surface roughness might not be representative of tokamak plasma-facing surfaces.

Objectives

Methods

Results

Conclusion