Speaker
Sergey Pestchanyi
(INR)
Description
Transient heat fluxes onto the tungsten divertor targets during disruptions in ITER may cause severe melting, leading to intolerable damage. However, for sufficiently energetic transients, tungsten vaporized from the target in the initial stage of the heat pulse will generate a protective plasma shield in front of the target, greatly reducing the incoming heat flux. This vapour shielding is a complex process, combining MHD convection and diffusion of the plasma shield with conversion of the transient heat flux into radiation. It can only really be modelled by numerical simulations, which have been performed for ITER disruptions using the TOKES fluid plasma code, demonstrating significant heat flux mitigation[1].
Given the potential benefits of vapour shielding with regard to the damage which may be caused by unmitigated disruptions on ITER, these TOKES simulations require experimental verification. Although plasma conditions pertinent to high energy ITER disruptions (peak heat fluxes of tens of GWm-2-2 on ms timescales) cannot be created easily in the laboratory, some experimental data does exist from the 2MK-200 magnetic cusp facility, where tungsten vapour shielding has been observed under relevant heat fluxes (~100GW/m22), but on much faster timescales (tens of ms)[1]. This device provides plasma flow over 20 ms onto a tungsten target with measured plasma density ne=(1.5-2)×102222 m–3–3 and temperatures of Te=250eV and Ti=800eV.
This paper will describe the first ever simulation of this 2MK-200 transient vapour shield, using the TOKES code configured to match the magnetic configuration to the 2MK-200 cusp and the plasma parameters. The results are in reasonable agreement with the measured maximum density, the plasma shield width and the Te profiles.
[1]S. Pestchanyi et al, accepted for publication in Fusion Engineering and Design
[2]Arkhipov, et al, Plasma Phys. Rep. 20 (1994) 782
Co-authors
Richard Pitts
(Science Division, ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance, France)
Sergey Pestchanyi
(INR, KIT, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen, Germany)
Valery Safronov
(First Wall Section, Russian Federation ITER Domestic Agency, Kurchatov sq.1, 123182, Moscow, Russian Federation)
