P2.141 in 31st EPS

TSC Simulation of ITB Crash and Following Disruption Dynamics on JT-60U High-beta Reversed Shear Plasmas

Steady-state operation of advanced tokamak reactors requires development of disruption mitigation by reducing speed of plasma current quench to attain high- , high-performance fusion plasmas. In JT-60U Reversed Shear (RS) plasmas with a high BootStrap (BS) current fraction, however, a fast current quench of major disruptions was recently observed [1]. Hence, an understanding of disruption characteristics of high- , RS plasmas is particularly important for designing high performance tokamak reactors, where the locality of the BS current generated by the Internal Transport Barrier (ITB) is closely linked with the magnetic shear profile. This paper presents a detailed process of the ITB crash and following disruption dynamics of RS plasmas through an axisymmetric MHD simulation using the Tokamak Simulation Code (TSC) [2].

By modeling an abrupt disappearance of the high- core region inside the ITB and a simultaneous destruction of magnetic surfaces or "magnetic braiding" [4, 5, 6], selfconsistent time-evolutions of profiles of the ITB-generated BS current, the induced ohmic current and the loop voltage were demonstrated for thermal quench triggered by the ITB crash [3] and following current quench. Particular features of disruption dynamics of high RS plasmas were clarified to be a dramatic change of the current profile to one with positive shear and an associated property of the fast current quench. These TSC results were directly compared with a typical disruption of JT-60U high- RS plasma, taking special notice of an impulsive current spike at thermal quench and quench speed of the plasma current. Detailed discussions about the governing mechanism for disruption behavior of strong ITB, RS plasmas will be given at the forthcoming EPS conference.

[1] Y. Kawano et al., 30th EPS, P-2.129, St Petersburg, 2003.
[2] S.C. Jardin, N. Pomphery and J. Delucia, J. Comput. Phys. 66, 481 (1986).
[3] N. Takei et al., 13th International Toki Conference, P2-27, Toki, 2003.
[4] A.H. Boozer, Plasma Physics 35, 133 (1986).
[5] P.L. Taylor, A.G. Kellman et al., Phys. Rev. Lett. 76, 916 (1996).
[6] N. Takei et al., 30th EPS, P-2.127, St Petersburg, 2003.