V.N. Litunovsky, V.E. Kuznetsov, I.B. Ovchinnikov, V.A. Titov
D.V. Efremov Scientific Research Institute of Electrophysical Apparatus
189631, St. Petersburg, Russia
A key problem in the International Thermonuclear Experimental Reactor (ITER) design is to predict the plasma-facing component (PFC) lifetimes in off-normal events---plasma disruptions and Edge Localized Modes (ELMs). Clear knowledge is needed, not only of the absorbed energy values for various materials at any of the expected parameters of in-cident power, but also an understanding of the role of each type of melt layer dynamics (instabilities, volumetric boiling, etc.) in the total erosion of metals (Be, W).
Some new data on the material response of Al, Cu, W, and graphite in disruption simu-lation experiments on the "VIKA" facility [1] is presented. The VIKA long-pulse plasma accelerator---the source of a high heat flux plasma---is able to produce plasma streams with quasi-stationary specific energy levels during the pulse duration (up to w=30 MJ/m2). A pulse forming network (PFN) permits the formation of a rectangular current pulse in the gun at t=0.09-1.2 ms (t<0.36 ms in the experiments to be described).
The dynamics of material reactions was studied for fixed levels of irradiation power (~100 GW/m2) at various pulse durations. The coefficient of absorbed energy is shown to fall with both time and growth of plasma load. Melt layer splashing for the time period t>0.18 ms is the primary contributor to mass losses and the erosion depth of Al. For W, liquid layer instability results in the local thinning of the melt layer. Furthermore, the pre-liminary heating of W samples leads to increasing instability increments (up to 250 mm for T=1000 C). Preheating tungsten samples sufficiently controls the intensity of crack-ing and spalling. The suppression of plasma movement along the surface is shown to limit both the erosion depth and the circulation of erosion products.
Some experiments have been carried out in the presence of normal and inclined mag-netic fields (B<5T). The results of studies of the influence of a magnetic field on material responses is discussed.
REFERENCES
1. V.N. Litunovskly, I.B. Ovchinnikov, A.A. Drozdov et al., Study of material response on simulated ITER disruptive plasma heat load with variable duration, IEEE/NPSS 16th Symposium Fusion Engineering, eds. G.H. Miley and C.M. Elliott, IEEE, Pis-cataway, NJ, Vol. 1, pp. 435-438 (1996).