Simulations of thermionic suppression during tungsten transient melting experiments

0482343 - ÚFP 2018 RIV SE eng J - Journal Article
Komm, Michael - Tolias, P. - Ratynskaia, S. - Dejarnac, Renaud - Gunn, J. P. - Krieger, K. - Podolník, Aleš - Pitts, R.A. - Pánek, Radomír
Simulations of thermionic suppression during tungsten transient melting experiments.
Physica Scripta. T170, December (2017), č. článku 014069. ISSN 0031-8949. E-ISSN 1402-4896.
[PFMC 2017: 16th International Conference on Plasma-Facing Materials and Components for Fusion Applications. Düsseldorf, 16.05.2017-19.05.2017]
R&D Projects: GA ČR(CZ) GA16-14228S; GA MŠMT(CZ) 8D15001
EU Projects: European Commission(XE) 633053 - EUROfusion
Institutional support: RVO:61389021
Keywords : tokamak * thermionic emission * tungsten * melt * plasma-facing component
OECD category: 1.3 Physical sciences
Impact factor: 1.902, year: 2017
http://iopscience.iop.org/article/10.1088/1402-4896/aa9209

Plasma-facing components receive enormous heat fluxes under steady state and especially during transient conditions that can even lead to tungsten (W) melting. Under these conditions, the unimpeded thermionic current density emitted from the W surfaces can exceed the incident plasma current densities by several orders of magnitude triggering a replacement current which drives melt layer motion via the J x B force. However, in tokamaks, the thermionic current is suppressed by space-charge effects and prompt re-deposition due to gyro-rotation. We present comprehensive results of particle-in-cell modelling using the 2D3V code SPICE2 for the thermionic emissive sheath of tungsten. Simulations have been performed for various surface temperatures and selected inclinations of the magnetic field corresponding to the leading edge and sloped exposures. The surface temperature dependence of the escaping thermionic current and its limiting value are determined for various plasma parameters, for the leading edge geometry, the results agree remarkably well with the Takamura analytical model. For the sloped geometry, the limiting value is observed to be proportional to the thermal electron current and a simple analytical expression is proposed that accurately reproduces the numerical results.
Permanent Link: http://hdl.handle.net/11104/0277837