Internal transport barrier triggering by rational magnetic flux surfaces in tokamaks

The formation of internal transport barriers (ITBs) has been experimentally associated with the presence of rational q surfaces in both JET and ASDEX Upgrade. The triggering mechanisms are related to the occurrence of magneto-hydrodynamic (MHD) instabilities such as mode coupling and fishbone activity. These events could locally modify the poloidal velocity and increase transiently the shearing rate to values comparable with the linear growth rate of ion temperature gradient modes. For JET reversed magnetic shear scenarios, ITB emergence occurs preferentially when the minimum q reaches an integral value. In this case, transport effects localized in the vicinity of zero magnetic shear and close to rational q values may be at the origin of ITB formation. The role of rational q surfaces in ITB triggering stresses the importance of q profile control for an advanced tokamak scenario and could assist in substantially lowering the access power to these scenarios in next step facilities.

[1]  J. Weiland,et al.  Micro-stability and transport modelling of internal transport barriers on JET , 2003 .

[2]  A. Murari,et al.  LETTER TO THE EDITOR: Active control of the current density profile in JET , 2003 .

[3]  C. Giroud,et al.  Progress towards steady-state operation and real-time control of internal transport barriers in JET , 2003 .

[4]  W. Houlberg,et al.  Plasma and momentum transport processes in the vicinity of a magnetic island in a tokamak , 2003 .

[5]  E. Joffrin,et al.  Triggering of internal transport barrier in JET , 2002 .

[6]  The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport , 2002 .

[7]  X. Litaudon,et al.  A dimensionless criterion for characterizing internal transport barriers in JET , 2002 .

[8]  F. Imbeaux,et al.  Progress in internal transport barrier plasmas with lower hybrid current drive and heating in JET (Joint European Torus) , 2002 .

[9]  E. Joffrin,et al.  MHD internal transport barrier triggering in low positive magnetic shear scenarios in JET , 2002 .

[10]  T Tokuzawa,et al.  Observation of plasma flow at the magnetic island in the large helical device. , 2001, Physical review letters.

[11]  X. Litaudon,et al.  Electron heated internal transport barriers in JET , 2002 .

[12]  Alain Becoulet,et al.  JET progress towards an advanced mode of ITER operation with current profile control , 2001 .

[13]  Ambrogio Fasoli,et al.  MHD Spectroscopy through Detecting Toroidal Alfvén Eigenmodes and Alfvén Wave Cascades , 2001 .

[14]  C. D. Challis,et al.  Effect of q-profile modification by LHCD on internal transport barriers in JET*Effect of q-profile m , 2001 .

[15]  C. Bourdelle,et al.  Global simulations of ion turbulence with magnetic shear reversal , 2001 .

[16]  H. R. Wilson,et al.  The role of polarization current in magnetic island evolution , 2001 .

[17]  J. Hobirk,et al.  MHD Phenomena as Trigger for the Formation of Internal Transport Barriers on ASDEX Upgrade , 2001 .

[18]  A. Thyagaraja,et al.  Numerical simulations of tokamak plasma turbulence and internal transport barriers , 2000 .

[19]  B. Carreras,et al.  Generation of sheared poloidal flows via Reynolds stress and transport barrier physics , 2000 .

[20]  Bartlett,et al.  Suppression of plasma turbulence during optimized shear configurations in JET , 2000, Physical review letters.

[21]  C. Gormezano,et al.  High performance tokamak operation regimes , 1999 .

[22]  Core Transport Reduction in Tokamak Plasmas with Modified Magnetic Shear , 1999 .

[23]  N. J. Lopes Cardozo,et al.  A model for electron transport barriers in tokamaks, tested against experimental data from RTP , 1998 .

[24]  Herbert L Berk,et al.  The HAGIS self-consistent nonlinear wave-particle interaction model , 1998 .

[25]  R. Jaenicke,et al.  Confinement in W7-AS and the role of radial electric field and magnetic shear , 1997 .

[26]  J. Weiland,et al.  Analysis of eta i mode by reactive and dissipative descriptions and the effects of magnetic q and negative shear on the transport , 1997 .

[27]  K. H. Burrell,et al.  Effects of E×B velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices , 1997 .

[28]  X. Litaudon,et al.  Full steady-state operation in Tore Supra , 1996 .

[29]  C. Laviron,et al.  Stationary regimes of improved confinement in Tore Supra , 1996 .

[30]  M. Mauel,et al.  Demonstration of high‐performance negative central magnetic shear discharges in the DIII‐D tokamak , 1996 .

[31]  Manickam,et al.  Improved confinement with reversed magnetic shear in TFTR. , 1995, Physical review letters.

[32]  K. H. Burrell,et al.  Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma , 1995 .

[33]  Tsuji,et al.  Internal transport barrier on q=3 surface and poloidal plasma spin up in JT-60U high- beta p discharges. , 1994, Physical review letters.

[34]  F. Romanelli,et al.  The radial structure of the ion‐temperature‐gradient‐driven mode , 1993 .

[35]  D. Edery,et al.  Toroidal coupling and frequency spectrum of tearing modes , 1990 .

[36]  A. Samain.  Diamagnetic destabilization of magnetic islands in the non-linear regime , 1984 .