Analysis and modelling of power modulation experiments in JET plasmas with internal transport barriers

Understanding the physics of internal transport barriers (ITBs) is a crucial issue in developing ITER relevant advanced tokamak scenarios. To gain new information on ITBs, RF power modulation experiments, mainly devoted to the study of electron heat transport through ITBs, have been performed on the JET tokamak. The main physics results have been reported in [1]. The present paper describes in detail the data analysis and numerical modelling work carried out for the interpretation of the experiments. ITBs located in the negative shear region behave as localized insulating layers able to stop the heat wave propagation, thus implying that the ITB is a region of low diffusivity characterized by a loss of stiffness. Various sources of spurious effects affecting the interpretation of the results are analysed and discussed. First principle based models have so far failed to predict the temperature profile in the first place, which prevented their application to modulation results, while empirical transport models have been set up and reproduce the major part of the data.

[1]  P. Hennequin,et al.  ICRF power deposition profile and determination of the electron thermal diffusivity by modulation experiments in JET , 1990 .

[2]  L. L. Lao,et al.  Equilibrium analysis of current profiles in tokamaks , 1990 .

[3]  P. Mantica,et al.  Determination of diffusive and nondiffusive transport in modulation experiments in plasmas , 1991 .

[4]  P. Diamond,et al.  Neoclassical poloidal and toroidal rotation in tokamaks , 1991 .

[5]  T. Hellsten,et al.  Comparison of time dependent simulations with experiments in ion cyclotron heated plasmas , 1993 .

[6]  R. Waltz,et al.  A gyro-Landau-fluid transport model , 1997 .

[7]  N. C. Hawkes,et al.  DESIGN OF THE JOINT EUROPEAN TORUS MOTIONAL STARK EFFECT DIAGNOSTIC , 1999 .

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

[9]  Experimental studies of electron transport , 2001 .

[10]  C. Giroud,et al.  ERRATUM: Influence of the q-profile shape on plasma performance in JET , 2002 .

[11]  D. Van Eester,et al.  Re-evaluation of ITER ion cyclotron operating scenarios , 2002 .

[12]  Taina Kurki-Suonio,et al.  Formation and detection of internal transport barriers in low-current tokamaks , 2002 .

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

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

[15]  C. D. Challis,et al.  Internal transport barrier triggering by rational magnetic flux surfaces in tokamaks , 2003 .

[16]  P. C. de Vries,et al.  Recent 3He Radio Frequency Heating Experiments On JET , 2003 .

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

[18]  F. Leuterer,et al.  Modulated ECRH power deposition in ASDEX Upgrade , 2003 .

[19]  E D'Azevedo,et al.  Sheared poloidal flow driven by mode conversion in tokamak plasmas. , 2003, Physical review letters.

[20]  E. Joffrin,et al.  Localized bulk electron heating with ICRF mode conversion in the JET tokamak , 2004 .

[21]  Jeff M. Candy,et al.  Smoothness of turbulent transport across a minimum-q surface , 2004 .

[22]  J. Weiland,et al.  Fully predictive time-dependent transport simulations of ITB plasmas in JET, JT-60U and DIII-D , 2006 .

[23]  Probing internal transport barriers with heat pulses in JET. , 2006, Physical review letters.