Electron thermal transport analysis in Tokamak a Configuration Variable
- Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas Association Euratom-Confederation Suisse, CH-1015 Lausanne (Switzerland)
- Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)
A Tokamak a Configuration Variable (TCV) [G. Tonetti, A. Heym, F. Hofmann et al., in Proceedings of the 16th Symposium on Fusion Technology, London, U.K., edited by R. Hemsworth (North-Holland, Amsterdam, 1991), p. 587] plasma with high power density (up to 8 MW/m{sup 3}) core deposited electron cyclotron resonance heating at significant plasma densities ({<=}7x10{sup 19} m{sup -3}) is analyzed for the electron thermal transport. The discharge distinguishes itself as it has four distinct high confinement mode (H-mode) phases. An Ohmic H-mode with type III edge localized modes (ELMs), which turns into a type I ELMy H-mode when the ECRH is switched on. The ELMs then vanish, which gives rise to a quasistationary ELM-free H-mode. This ELM-free phase can be divided into two, one without magnetohydrodynamics (MHD) and one with. The MHD mode in the latter case causes the confinement to drop by {approx}15%. For all four phases both large-scale trapped electron (TEM) and ion temperature gradient (ITG) modes and small-scale electron temperature gradient (ETG) modes are analyzed. The analytical TEM formulas have difficulty in explaining both the magnitude and the radial profile of the electron thermal flux. Collisionality governs the drive of the TEM, which for the discharge in question implies it can be driven by either the temperature or density gradient. The TEM response function is derived and it is shown to be relatively small and to have sharp resonances in its energy dependence. The ETG turbulence, predicted by the Institute for Fusion Studies electron gyrofluid code, is on the other hand driven solely by the electron temperature gradient. Both trapped and passing electrons add to the ETG instability and turbulent thermal flux. For easy comparison of the results of the above approaches and also with the Weiland model, a dimensionless error measure, the so-called average relative variance is introduced. According to this method the ETG model explains 70% of the variation in the electron heat diffusivity whereas the predictive capabilities of the TEM-ITG models are poor. These results for TCV support the conclusion that the ETG model is able to explain a wide range of anomalous electron transport data, in addition to existing evidence from ASDEX [F. Ryter, F. Leuterer, G. Pereverzev, H.-U. Fahrbach, J. Stober, W. Suttrop, and the ASDEX Upgrade Team, Phys. Rev. Lett. 86, 2325 (2001)], Tore Supra [G. T. Hoang, W. Horton, C. Bourdelle, B. Hu, X. Garbet, and M. Ottaviani, Phys. Plasmas 10, 405 (2003)] and the Frascati Tokamak Upgrade [A. Jacchia, F. D. Luca, S. Cirant, C. Sozzi, G. Bracco, A. Brushi, P. Buratti, S. Podda, and O. Tudisco, Nucl. Fusion 42, 1116 (2002)].
- OSTI ID:
- 21120514
- Journal Information:
- Physics of Plasmas, Vol. 15, Issue 8; Other Information: DOI: 10.1063/1.2965828; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA). TCV TEAM; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ASDEX TOKAMAK
ECR HEATING
EDGE LOCALIZED MODES
ELECTRON TEMPERATURE
FT TOKAMAK
H-MODE PLASMA CONFINEMENT
ION TEMPERATURE
MAGNETOHYDRODYNAMICS
PLASMA
PLASMA DENSITY
RESPONSE FUNCTIONS
RF SYSTEMS
TCV TOKAMAK
TEMPERATURE GRADIENTS
TORE SUPRA TOKAMAK
TRANSMISSION ELECTRON MICROSCOPY
TRAPPED ELECTRONS