Density dependence of trace tritium transport in H-mode Joint European Torus plasma

Abstract

Tritium transport in edge localized mode (ELM) high confinement (H-mode) plasmas is analyzed here as a function of density for discharges from the recent trace tritium experimental campaign performed on Joint European Torus. In this campaign small amounts of tritium have been puffed or injected (with neutral beam injectors) into deuterium plasmas [K.-D. Zastrow, J. M. Adams, Yu. Baranov et al., Plasma Phys. Controlled Fusion 46, B255 (2004)]. Information about the tritium has been obtained from the evolution of the profiles of neutron emission simulated via the TRANSP [R. J. Goldston, D. C. McCune, H. H. Towner, S. L. Davis, R. J. Hawryluk, and G. L. Schmidt, J. Comput. Phys. 43, 61 (1981)] and SANCO (L. Lauro-Taroni, B. Alper, R. Giannella, K. Lawson, F. Marcus, M. Mattioli, P. Smeulders, and M. Von Hellermann, Proceedings of the 21st European Conference on Controlled Fusion and Plasma Physics, Montpelier, France, 1994) codes. A strong inverse correlation of tritium transport with plasma density is found in this analysis. The low tritium transport at high density is close to neoclassical values while the transport becomes strongly anomalous in low density plasmas. The thermal transport does not exhibit such a strong density dependence, leading to a varying ratio of thermal to tritium transport in these discharges. An interpretation of the density effects on the trace tritium transport, partially based on the test particle simulations in plasmas with stochastic magnetic field, is proposed. A simple model for the tritium diffusion coefficient and convective velocity, which includes the modification of the neoclassical particle diffusion in presence of electromagnetic turbulence [A. I. Smolyakov and P. N. Yushmanov, Nucl. Fusion 35, 383 (1993)] completed with an empirical density dependence, is developed. This model has positive β dependence in agreement with the results of the similarity experiments performed for trace tritium transport.