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Title: Probing Internal Transport Barriers with Heat Pulses in JET

Abstract

The first electron temperature modulation experiments in plasmas characterized by strong and long-lasting electron and ion internal transport barriers (ITB) have been performed in JET using ion cyclotron resonance heating in mode conversion scheme. The ITB is shown to be a well localized narrow layer with low heat diffusivity, characterized by subcritical transport and loss of stiffness. In addition, results from cold pulse propagation experiments suggest a second order transition process for ITB formation.

Authors:
 [1];  [2]; ; ; ; ;  [3]; ; ;  [4];  [5]; ; ; ; ; ; ;  [6];  [7]
  1. Istituto di Fisica del Plasma 'P.Caldirola', Associazione Euratom-ENEA-CNR, Milan (Italy)
  2. LPP-ERM/KMS, Association Euratom-Belgian State, TEC, B-1000 Brussels (Belgium)
  3. CEA Cadarache, Association Euratom-CEA, St Paul-lez-Durance Cedex (France)
  4. Helsinki University of Technology, Association Euratom-Tekes, P.O.Box 2200 (Finland)
  5. Dipartimento di Ingegneria Nucleare, Politecnico di Milano, Milan (Italy)
  6. Culham Science Centre, EURATOM/UKAEA Fusion Association, Oxon. OX14 3DB (United Kingdom)
  7. Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Garching (Germany)
Publication Date:
OSTI Identifier:
20777078
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 96; Journal Issue: 9; Other Information: DOI: 10.1103/PhysRevLett.96.095002; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHARGED-PARTICLE TRANSPORT; ELECTRON TEMPERATURE; ELECTRONS; HEAT; ICR HEATING; ION TEMPERATURE; IONS; MODE CONVERSION; PLASMA; PLASMA CONFINEMENT; PLASMA DIAGNOSTICS; PULSES; THERMAL BARRIERS; TOKAMAK DEVICES

Citation Formats

Mantica, P., Van Eester, D., Garbet, X., Laborde, L., Mazon, D., Moreau, D., Joffrin, E., Imbeaux, F., Mantsinen, M., Salmi, A., Marinoni, A., Hawkes, N., Kiptily, V., Sharapov, S., Thyagaraja, A., Voitsekhovitch, I., Vries, P. de, Zastrow, K.-D., and Pinches, S. Probing Internal Transport Barriers with Heat Pulses in JET. United States: N. p., 2006. Web. doi:10.1103/PhysRevLett.96.095002.
Mantica, P., Van Eester, D., Garbet, X., Laborde, L., Mazon, D., Moreau, D., Joffrin, E., Imbeaux, F., Mantsinen, M., Salmi, A., Marinoni, A., Hawkes, N., Kiptily, V., Sharapov, S., Thyagaraja, A., Voitsekhovitch, I., Vries, P. de, Zastrow, K.-D., & Pinches, S. Probing Internal Transport Barriers with Heat Pulses in JET. United States. doi:10.1103/PhysRevLett.96.095002.
Mantica, P., Van Eester, D., Garbet, X., Laborde, L., Mazon, D., Moreau, D., Joffrin, E., Imbeaux, F., Mantsinen, M., Salmi, A., Marinoni, A., Hawkes, N., Kiptily, V., Sharapov, S., Thyagaraja, A., Voitsekhovitch, I., Vries, P. de, Zastrow, K.-D., and Pinches, S. Fri . "Probing Internal Transport Barriers with Heat Pulses in JET". United States. doi:10.1103/PhysRevLett.96.095002.
@article{osti_20777078,
title = {Probing Internal Transport Barriers with Heat Pulses in JET},
author = {Mantica, P. and Van Eester, D. and Garbet, X. and Laborde, L. and Mazon, D. and Moreau, D. and Joffrin, E. and Imbeaux, F. and Mantsinen, M. and Salmi, A. and Marinoni, A. and Hawkes, N. and Kiptily, V. and Sharapov, S. and Thyagaraja, A. and Voitsekhovitch, I. and Vries, P. de and Zastrow, K.-D. and Pinches, S.},
abstractNote = {The first electron temperature modulation experiments in plasmas characterized by strong and long-lasting electron and ion internal transport barriers (ITB) have been performed in JET using ion cyclotron resonance heating in mode conversion scheme. The ITB is shown to be a well localized narrow layer with low heat diffusivity, characterized by subcritical transport and loss of stiffness. In addition, results from cold pulse propagation experiments suggest a second order transition process for ITB formation.},
doi = {10.1103/PhysRevLett.96.095002},
journal = {Physical Review Letters},
number = 9,
volume = 96,
place = {United States},
year = {Fri Mar 10 00:00:00 EST 2006},
month = {Fri Mar 10 00:00:00 EST 2006}
}
  • New results on electron heat wave propagation using ion cyclotron resonance heating power modulation in the Joint European Torus (JET) [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] plasmas characterized by internal transport barriers (ITBs) are presented. The heat wave generated outside the ITB, and traveling across it, always experiences a strong damping in the ITB layer, demonstrating a low level of transport and loss of stiffness. In some cases, however, the heat wave is strongly inflated in the region just outside the ITB, showing features of convective-like behavior. In other cases, a second maximum in the perturbationmore » amplitude is generated close to the ITB foot. Such peculiar types of behavior can be explained on the basis of the existence of a critical temperature gradient length for the onset of turbulent transport. Convective-like features appear close to the threshold (i.e., just outside the ITB foot) when the value of the threshold is sufficiently high, with a good match with the theoretical predictions for the trapped electron mode threshold. The appearance of a second maximum is due to the oscillation of the temperature profile across the threshold in the case of a weak ITB. Simulations with an empirical critical gradient length model and with the theory based GLF23 [R. E. Waltz et al., Phys. Plasmas, 4, 2482 (1997)] model are presented. The difference with respect to previous results of cold pulse propagation across JET ITBs is also discussed.« less
  • The formation of internal transport barriers observed in both Joint European Torus (JET) [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)] and Doublet III-D Tokamak (DIII-D) [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] are reproduced in predictive transport simulations. These simulations are carried out for two JET-optimized shear discharges and two DIII-D negative central shear discharges using the Multi-Mode model in the time-dependent 1-1/2-D BALDUR transport code [C. E. Singer et al., Comput. Phys. Commun. 49, 275 (1988)]. The Weiland model is used for drift modes in themore » Multi-Mode model in combination with either Hahm-Burrell or Hamaguchi-Horton flow shear stabilization mechanisms, where the radial electric field is inferred from the measured toroidal velocity profile and the poloidal velocity profile computed using neoclassical theory. The transport barriers are apparent in both the ion temperature and thermal diffusivity profiles of the simulations. The timing and location of the internal transport barriers in the simulations and experimental data for the DIII-D cases are in good agreement, though some differences remain for the JET discharges. The formations of internal transport barriers are interpreted as resulting from a combination of ExB flow shear and weak magnetic shear mechanisms. (c) 2000 American Institute of Physics.« less
  • Previous results from the analysis of fully non inductively sustained electron internal transport barriers (eITBs) in TCV show that a strong coupling exists between electron temperature and density profiles inside the barrier. A phenomenology that is completely different from the standard L-mode is observed . New experimental results assess transient phases to calculate particle convection and diffusion coefficients, allowing also to discuss the role of neoclassical transport. Gyrokinetic and gyrofluid analysis of steady-state eITBs provide tools to understand the mechanism that drive the observed density peaking in advanced scenarios with internal transport barriers and dominant electron heating.
  • Models with critical gradients are widely used to describe energy balance in L-mode discharges. The so-called first critical gradient can be found from the canonical temperature profile. Here, it is suggested that discharge regimes with transport barriers can be described based on the idea of the second critical gradient. If, in a certain plasma region, the pressure gradient exceeds the second critical gradient, then the plasma bifurcates into a new state and a transport barrier forms in this region. This idea was implemented in a modified canonical profile transport model that makes it possible to describe the energy and particlemore » balance in tokamak plasmas with arbitrary cross sections and aspect ratios. The magnitude of the second critical gradient was chosen by comparing the results calculated for several tokamak discharges with the experimental data. It is found that the second critical gradient is related to the magnetic shear s. The criterion of the transport barrier formation has the form (a{sup 2}/r)d/drln(p/p{sub c}) > z{sub 0}(r), where r is the radial coordinate, a is the plasma minor radius, p is the plasma pressure, p{sub c} is the canonical pressure profile, and the dimensionless function z{sub O}(r) = C{sub O} + C{sub 1}s (with C{sub 0i} {approx}1, C{sub 0e} {approx}3, and C{sub 1i,e} {approx}2) describes the difference between the first and second critical gradients. Simulations show that this criterion is close to that obtained experimentally in JET. The model constructed here is used to simulate internal transport barriers in the JET, TFTR, DIII-D, and MAST tokamaks. The possible dependence of the second critical gradient on the plasma parameters is discussed.« less
  • We study the interplay between intrinsic rotation and internal transport barrier (ITB) dynamics through the dynamic change of the parallel Reynolds stress. Global flux-driven gyrofluid simulations are used for this study. In particular, we investigate the role of parallel velocity gradient instability (PVGI) in the ITB formation and the back transition. It is found that the excitation of PVGI is followed by a change in the Reynolds stress which drives a momentum redistribution. This significantly influences E Multiplication-Sign B shear evolution and subsequent ITB dynamics. Nonlocal interactions among fluctuations are also observed during the PVGI excitation, resulting in turbulence suppressionmore » at the ITB.« less