DIAGNOSTICS OF NEAR-SURFACE PLASMA LAYERS PRODUCED BY HIGH-POWER PLASMA-FLOW INTERACTION WITH A SOLID MATERIAL BARRIER UNDER CONDITIONS CLOSE TO THE CURRENT DISRUPTION THERMAL STAGE IN AN ITER-TYPE TOKAMAK

Using optospectral and calorimetry techniques, the study of the transi tional layer dynamics due to plasma flux interaction with a target sur face was performed. Plasma flow was produced by the quasi-stationary p lasma accelerator QSPA Kh-50. Time-space dependences were obtained for density distribution of electrons n(e) and hydrogen atoms in both the ground n0 and excited n(alpha) states. The temporal variation of the density gradient was studied. The velocity and power density of the in cident plasma flow were estimated. It was shown that the incident flow with approximately 10(16) cm-3 density and 2 - 4 x 10(7) cm/s maximum velocity (corresponding power density flux is 1 kJ for less-than-or-s imilar-to 100 mus pulse duration) produced a near-surface layer with t he density of 10(-17) cm-3 (where n(alpha) and no are about 10(14) cm- 3. This layer existed during the whole time of the flow interaction. T he thickness of the layer changed from 2 - 3 mm to 10 - 15 mm during t he time of interaction. The lines of the elements of the target materi al and plasma flow were observed in the spectrum of the near-surface l ayer. It was found that the absorbed energy amounted to 90% of the tot al energy of the flow.