Theory of Plasma Instabilities: Transport, Stability, and Their Interactions

Papers from the Second IAEA Technical Meeting on the
Theory of Plasma Instabilities: Transport, Stability, and Their Interactions
Miramare, Trieste, Italy, 2-4 March 2005
Sponsoring Institutions
International Atomic Energy Agency
The Abdus Salam International Centre for Theoretical Physics
Director
Artur Malaquias
International Atomic Energy Agnecy, Vienna, Austria
Local Organizer
Brian Stewart
The Abdus Salam International Centre for Theoretical Physics,
Trieste, Italy
Editor
Ronald C. Davidson
Princeton Plasma Physics Laboratory, Princeton, NJ
Physics of Plasmas
Volume 12, Issue 9, September 2005
Preface: Theory of plasma instabilities: Transport, stability,
and their interactions
T. S. Hahm
Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543
Received 5 August 2005; accepted 5 August 2005; published online 21 September 2005.
 2005 American Institute of Physics. 'DOI: 10.1063/1.2043007'

Magnetic confinement theory has become more sophisticated and realistic in recent years as more useful guidance became available from simulations and experiments. The conventional approach based on local theory is being modified by recognition of the importance of nonlocal phenomena such as turbulence spreading and relaxation at large scales. More self-consistent analytical models of turbulence regulation by zonal flows began to emerge, superceding the previous kinematic passive scalar models of shear suppression of turbulence. As H-mode transition models become more mature, some experimentally testable novel properties of the predator-prey model are being studied and the role of poloidal asymmetry is being explored, addressing the twodimensional structure of turbulence. Basic experiments are now performed to understand the detailed structures of plasmas turbulence. Useful codes are being developed to study the mesoscale phenomena beyond typical microturbulence scales. Finally, the kinetic effects of an anisotropic energetic particle distribution function on magnetohydrodynamic @MHD. instabilities are taken into account.

The following seven papers, which were presented at the Second International Atomic Energy Agency Technical Meeting on the Theory of Plasma Instabilities: Transport, Stability, and their Interaction, exemplify well the aforementioned forefronts of research in this area. The meeting was held in the Abdus Salam International Center for Theoretical Physics, Miramare, Trieste, Italy, from March 2nd to March 4th, 2005.

Kim's paper presents detailed analytical calculations of the zonal flow-induced shearing of turbulence using the interchange turbulence model. Due to the spatiotemporal variations of zonal flows, there exist several asymptotic regimes. The most robust feature of Kim's findings is that most of the reduction in the radial flux is due to the strong reduction in the radial velocity of turbulence. On the other hand, the change in the cross phase between density fluctuations and the radial velocity due to zonal flows was weak. A simple dynamical model of the inward spreading of edge turbulence towards the core is studied in Hahm's paper. The related gyrokinetic particle simulations of toroidal ion temperature gradient @ITG. turbulence spreading has been also performed using the gyrokinetic toroidal code @GTC. for the case of radially increasing ion temperature gradient. Due to turbulence spreading from the edge, the turbulence intensity in the core region is significantly enhanced over the value obtained from simulations of the core region only. The scaling of the turbulence front propagation speed is closer to the prediction from a nonlinear diffusion model than one based on linear toroidal coupling.

Ball's paper contains the results from the three-field version of the predator-prey model of the L-H transition. Bifurcation from an L-mode-like solution to an H-mode-like solution has been found, as predicted before. A novel feature of Ball's results is the existence of a solution, which has the unexpected favorable property that, as the input power is reduced, the poloidal velocity increases.

A two-dimensional model for shock formation in the pedestal that occurs in H-mode plasmas with poloidal Mach numbers above unity is presented in Kasuya's paper. It is predicted that the density and electric field will be nonuniform in the poloidal direction, leading to a nonvanishing particle pinch velocity which could be responsible for fast pedestal buildup.

Muller's paper reports the spatiotemporal evolution of turbulent fluctuations from the TORodial Plasma EXperiment @TORPEX. experiment as measured by the new HEXagonal Turbulence Imaging Probe @HEXTIP. diagnostic. The addition of a small vertical magnetic field to the toroidal magnetic field changes the turbulence and transport properties significantly.

The CUTIE code has been developed for studying interactions between microscale fluctuations and mesoscale MHD structures using a relatively simple plasma model. Thyagaraja's paper contains recent simulation results that are similar to a number of phenomena observed in tokamaks. For instance, a successful simulation of on- and off-axis sawteeth is presented.

Grave's paper describes calculations of the effect of auxiliary heating on sawteeth instabilities. The results are that, while rotation could influence the internal kink mode, the effect on ITER would be negligible. ITER-relevant stabilizing effects arise from unbalanced tangential neutral beam injection and anisotropy in the pressure due to the heating.

PHYSICS OF PLASMAS 12, 090901 @2005. 1070-664X/2005/12@9./090901/1/$22.50 12, 090901-1 2005 American Institute of Physics

more at http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PHPAEN@stand/phptitle1.pdf&idtype=standpdf

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