Sawtooth control experiments on ASDEX Upgrade

In a fusion device, the so-called sawtooth instability can lead to the triggering of confinement limiting neoclassical tearing modes. On the other hand, the existence of sawteeth is desirable for the removal of one fusion product, i.e. helium ash from the plasma core. This has led to great interest in the control of sawteeth. The sawtooth period can be changed drastically by local modification of the q-profile. In this paper, the influence of the beam line geometry of the neutral beam injection in the ASDEX Upgrade tokamak will be presented as well as the effect of local electron cyclotron current drive. Systematic scans in the electron cyclotron current deposition from the high-field side to the low-field side resolve areas with sawtooth stabilization and destabilization. These observations will be discussed, including modelling of the main results, with the ASTRA transport code constrained by experimental data.

[1]  R J Buttery,et al.  Destabilization of fast-ion-induced long sawteeth by localized current drive in the JET tokamak. , 2004, Physical review letters.

[2]  Olivier Sauter,et al.  Analysis of ion cyclotron heating and current drive at ω≈2ωcH for sawtooth control in JET plasmas* , 2002 .

[3]  M. Rosenbluth,et al.  Model for the sawtooth period and amplitude , 1996 .

[4]  R. Budny,et al.  Neutral beam stabilization of sawtooth oscillations in JET , 2002 .

[5]  Bhatnagar,et al.  Stabilization of sawteeth with additional heating in the JET tokamak. , 1988, Physical review letters.

[6]  R. J. Hawryluk,et al.  Neoclassical conductivity of a tokamak plasma , 1977 .

[7]  Sibylle Günter,et al.  Seed island of neoclassical tearing modes at ASDEX Upgrade , 1999 .

[8]  K. F. Mast,et al.  Overview of ASDEX Upgrade results—development of integrated operating scenarios for ITER , 2005 .

[9]  J. L. Soule,et al.  Internal kink modes in toroidal plasmas with circular cross sections , 1975 .

[10]  Olivier Sauter,et al.  Effects of localized electron heating and current drive on the sawtooth period , 2003 .

[11]  Olivier Sauter,et al.  Effect of triangular and elongated plasma shape on the sawtooth stability , 2000 .

[12]  O. Sauter,et al.  Control of neoclassical tearing modes by sawtooth control. , 2002, Physical review letters.

[13]  G. V. Pereverzev,et al.  TORBEAM, a beam tracing code for electron-cyclotron waves in tokamak plasmas , 2001 .

[14]  G. Fogaccia,et al.  On the stability of the internal kink mode in the banana regime , 1995 .

[15]  G. V. Pereverzew,et al.  ASTRA. An Automatic System for Transport Analysis in a Tokamak. , 1991 .