From MHD regime to quiescent non-inductive discharges in Tore Supra: experimental observations and MHD modelling

Attempts to run non-inductive plasma discharges on Tore Supra sometimes fail due to the triggering of magneto-hydro-dynamic (MHD) instabilities that saturate at a large amplitude, producing degraded confinement and loss of wave driven fast electrons (the so-called MHD regime (Maget et al 2005 Nucl. Fusion 45 69–80)). In this paper we investigate the transition to this soft (in the sense of non-disruptive) MHD limit from experimental observations, and compare it with non-linear code predictions. Such a comparison suggests that different non-linear regimes, with periodic relaxations or saturation, are correctly understood. However, successful non-inductive discharges without detectable magnetic island at q = 2 cannot be reproduced if realistic transport coefficients are used in the computation. Additional physics seems mandatory for explaining these discharges, such as diamagnetic effects, that could also justify cases of abrupt transition to the MHD regime.

[1]  John L. Johnson,et al.  Resistive instabilities in general toroidal plasma configurations , 1975 .

[2]  Resistive instabilities in a tokamak , 1976 .

[3]  J. Drake,et al.  Kinetic theory of tearing instabilities , 1977 .

[4]  B. V. Waddell,et al.  Tearing-mode activity for hollow current profiles , 1979 .

[5]  R. Carrera,et al.  Island bootstrap current modification of the nonlinear dynamics of the tearing mode , 1986 .

[6]  Semicollisional drift‐tearing modes in toroidal plasmas , 1986 .

[7]  A. Hassam,et al.  Analytical theory of nonlinear drift‐tearing mode stability , 1987 .

[8]  J. Manickam,et al.  Ideal MHD stability properties of pressure driven modes in low shear tokamaks , 1987 .

[9]  McGuire,et al.  Observation of ballooning modes in high-temperature tokamak plasmas. , 1992, Physical review letters.

[10]  A. Bondeson,et al.  The CHEASE code for toroidal MHD equilibria , 1996 .

[11]  McGuire,et al.  Off-Axis Sawteeth and Double-Tearing Reconnectionin Reversed Magnetic Shear Plasmas in TFTR. , 1996, Physical review letters.

[12]  F. C. Schüller,et al.  Electron thermal transport barrier and magnetohydrodynamic activity observed in Tokamak plasmas with negative central shear , 1997 .

[13]  MHD activity in FTU plasmas with reversed magnetic shear , 1997 .

[14]  J. P. Goedbloed,et al.  CASTOR: Normal-Mode Analysis of Resistive MHD Plasmas☆ , 1998 .

[15]  Frederic Imbeaux,et al.  Tomography of the fast electron bremsstrahlung emission during lower hybrid current drive on TORE SUPRA , 1999 .

[16]  T. Fujita,et al.  Resistive instabilities in reversed shear discharges and wall stabilization on JT-60U , 2002 .

[17]  Xavier Garbet,et al.  Nonlinear three-dimensional MHD simulations of tearing modes in tokamak plasmas , 2001 .

[18]  F. Imbeaux,et al.  MHD stability of lower hybrid enhanced performance discharges on the Tore Supra tokamak , 2001 .

[19]  F. Imbeaux,et al.  Simulations of steady-state scenarios for Tore Supra using the CRONOS code , 2003 .

[20]  L. L. Lao,et al.  Integrated, advanced tokamak operation on DIII-D , 2003 .

[21]  F. Imbeaux,et al.  MHD activity in Tore Supra gigajoule scenario , 2004 .

[22]  A. Becoulet,et al.  Recent fully non-inductive operation results in Tore Supra with 6?min, 1?GJ plasma discharges , 2004 .

[23]  M. Ottaviani,et al.  Multiple states of nonlinear drift-tearing islands. , 2004, Physical review letters.

[24]  F. Imbeaux,et al.  MHD stability of fully non-inductive discharges in Tore Supra , 2004, physics/0410181.

[25]  L. Gargiulo,et al.  Management of a water leak on actively cooled fusion devices , 2005 .

[26]  X. Garbet,et al.  MHD stability of (2,1) tearing mode: an issue for the preforming phase of Tore Supra non-inductive discharges , 2007 .

[27]  X. Garbet,et al.  Nonlinear magnetohydrodynamic simulation of Tore Supra hollow current profile discharges , 2007 .

[28]  Hinrich Lütjens,et al.  The XTOR code for nonlinear 3D simulations of MHD instabilities in tokamak plasmas , 2008, J. Comput. Phys..