The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Orbit-Following Simulation of Fast Ions in ASDEX Upgrade Tokamak in the Presence of Magnetic Ripple and Radial Electric Field

Ville Hynönen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium K216 at Helsinki University of Technology (Espoo, Finland) on the 18th of August, 2008, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9459-6)   [1668 KB]
Dissertation is also available in print (ISBN 978-951-22-9458-9)

Abstract

Magnetic confinement of plasma inside a tokamak is presently the most promising form of controlled fusion. A key issue for future fusion devices such as ITER is the interaction between the hot plasma and the cold material surfaces. The density control and exhaust of impurities must be effected in a way not causing excessive heat and particle loads. Edge localized modes (ELMs), intermittent bursts of energy and particles, characterize the standard high confinement (H)-mode. In the recently discovered quiescent H-mode (QH-mode), they are replaced by so-called edge harmonic oscillations of a more continuous nature. The QH-mode is obtained only with counter-injected neutral beams, indicating that fast ions may affect the edge stability properties and thus ELMs.

In this thesis, the neutral-beam-originated fast ions in ASDEX Upgrade tokamak are modelled using the orbit-following Monte Carlo code ASCOT. The modelling results include the edge fast ion slowing-down distribution and the surface loads caused by fast ion losses for co- and counter-injected neutral beams, corresponding to H-mode and QH-mode, respectively. The effects of magnetic field ripple, arising from the finite number of toroidal field coils, and radial electric field Er are included in the analysis. In addition to neutral beam ions, also the relation of surface distribution of tritium and the flux of tritons created in deuterium-deuterium fusion reactions is addressed.

Due to the difference in the direction of the gradient drift, counter-injected beams are prone to higher losses than co-injected beams. This leads to substantial wall loads, but also to higher edge fast ion density. Also the distribution of the fast ions in velocity space is different. The ripple-induced stochastic diffusion increases the losses, thereby increasing the wall load and reducing the density. The orbit width effects, squeezing for counter-injected and widening for co-injected beams, and orbit transitions caused by Er further increase the losses and wall load. Nevertheless, they also lead to higher edge fast ion density and changes in the velocity distribution. The obtained 4D distribution functions could be used for gaining insight into the roots of the QH-mode by analyzing the stability properties of the edge for the two injection directions.

This thesis consists of an overview and of the following 7 publications:

  1. W. Suttrop, V. Hynönen, T. Kurki-Suonio, P. T. Lang, M. Maraschek, R. Neu, A. Stäbler, G. D. Conway, S. Hacquin, M. Kempenaars, P. J. Lomas, M. F. F. Nave, R. A. Pitts, K.-D. Zastrow, the ASDEX Upgrade team, and contributors to the JET-EFDA workprogramme. 2005. Studies of the 'Quiescent H-mode' regime in ASDEX Upgrade and JET. Nuclear Fusion 45 (7) 721-730. © 2005 International Atomic Energy Agency (IAEA). By permission.
  2. V. Hynönen, T. Kurki-Suonio, W. Suttrop, R. Dux, K. Sugiyama, and the ASDEX Upgrade Team. 2006. ASCOT simulations of fast particle effects on ASDEX Upgrade edge. In: F. De Marco and G. Vlad (editors). Proceedings of the 33rd European Physical Society Conference on Plasma Physics. Rome, Italy. 19-23 June 2006. Europhysics Conference Abstracts, volume 30I, P-2.151, 4 pages. © 2006 European Physical Society (EPS). By permission.
  3. V. Hynönen, T. Kurki-Suonio, W. Suttrop, R. Dux, K. Sugiyama, and the ASDEX Upgrade Team. 2007. Surface loads and edge fast ion distribution for co- and counter-injection in ASDEX Upgrade. Plasma Physics and Controlled Fusion 49 (2) 151-174. © 2007 Institute of Physics Publishing. By permission.
  4. T. Kurki-Suonio, V. Hynönen, T. Ahlgren, K. Nordlund, K. Sugiyama, R. Dux, and the ASDEX Upgrade Team. 2007. Fusion tritons and plasma-facing components in a fusion reactor. Europhysics Letters 78 (6) 65002, 6 pages. © 2007 Europhysics Letters Association (EPLA). By permission.
  5. V. Hynönen and T. Kurki-Suonio. 2007. Erratum on surface loads and edge fast ion distribution for co- and counter-injection in ASDEX Upgrade. Plasma Physics and Controlled Fusion 49 (8) 1345-1347. © 2007 Institute of Physics Publishing. By permission.
  6. V. Hynönen, T. Kurki-Suonio, K. Sugiyama, R. Dux, A. Stäbler, T. Ahlgren, K. Nordlund, and the ASDEX Upgrade Team. 2007. Fusion tritons and plasma-facing components in a fusion reactor. In: P. Gąsior and J. Wołowski (editors). Proceedings of the 34th European Physical Society Conference on Plasma Physics. Warsaw, Poland. 2-6 July 2007. Europhysics Conference Abstracts, volume 31F, P-4.034, 4 pages. © 2007 European Physical Society (EPS). By permission.
  7. V. Hynönen, T. Kurki-Suonio, W. Suttrop, A. Stäbler, and the ASDEX Upgrade Team. 2008. Effect of radial electric field and ripple on edge neutral beam ion distribution in ASDEX Upgrade. Plasma Physics and Controlled Fusion 50 (3) 035014, 15 pages. © 2008 Institute of Physics Publishing. By permission.

Keywords: fusion, tokamak, Monte Carlo methods, fast particle effects, ASCOT code

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© 2008 Helsinki University of Technology

Last update 2011-05-26