(EX/P3-14) Interaction of T-10 Plasma with Impurity Pellets and Supersonic Gas Jet

V.Yu. Sergeev1), V.M. Timokhin1), V.G. Skokov1), B.V. Kuteev2), S.V. Krylov2), L.N. Khimchenko2), T-10 Team2)
1) State Polytechnical University, St. Petersburg, Russian Federation
2) Nuclear Fusion Institute, Russian Research Center “Kurchatov Institute”, Moscow, Russian Federation

Abstract.  Discharge control and diagnostics of high temperature plasma are important tasks of the controlled fusion program [ITER Physics Basis. Chapter 1 Nucl. Fusion 39 (1999) 2137]. Pellet and supersonic gas jet injection are tools for fuelling, diagnostics, wall conditioning and mitigation of major disruption [Kuteev B.V. Journal of Technical Physics 69 (1999) 63]. Recent results of T-10 experiment with impurity pellet injection and supersonic gas jet for studying and developing these applications are presented. Study of the effects during the pellet ablation phase (1 millisecond) with main objective to clarify the potential role of both MHD events in plasma initiated by pellet injection and pellet ablation bursts by supra-thermal electrons. It was observed that local bursts of pellet ablation appeared with increasing the pellet size while the plasma parameters were fixed. In the Li pellet experiments, fairly large cylindrical pellets were accelerated into T-10 ECRH heated plasmas. Effects of T-10 plasma response on Li pellet injection such as modifications of density and temperature profiles, snake formation are presented and described. Only weak effects of Li-wall conditioning were detected using impurity NIII, OII monitors and neutron rate signal. Reasons of this observation are discussed. The supersonic gas jet injection was arranged through a fast valve with a Laval nozzle. A forming of compact helium jets with supersonic 1.5 km/s velocity was expected. Injections were carried out in Ohmically heated plasma with ⟨ne⟩ = 3×1013 cm-3, I = 270 kA and the different 1.3×1019 (case I) and 3×1019 (case II) numbers of injected helium atoms. It was observed that for case I the jet penetrated up to 18 cm of the 30 cm plasma minor radius and the injected atom content was completely absorbed by plasma. Total electron content was doubled without deterioration of plasma conditions. It implies that the supersonic jet can be used for plasma fuelling. For case II, the jet injection caused the major disruption occurring at the density limit scenario. Experimental observation of jet penetration and absorption are compared with results of modeling.

Full paper available (PDF)