Turbulence and transport studies with phase contrast imaging in the Alcator C-Mod tokamak and comparisons with gyrokinetic simulations

An upgraded phase contrast imaging (PCI) diagnostic is used to study turbulence and transport in Alcator C-Mod. The upgraded PCI system is capable of measuring density fluctuations with high temporal (2 kHz-5 MHz) and wavenumber (0.5-55 cm-1) resolution. An upgrade of the system has enabled PCI to localize the short wavelength turbulence in the electron temperature gradient (ETG) range and resolve the direction of propagation (i.e., electron vs. ion diamagnetic direction) of the longer wavelength turbulence in the ion temperature gradient (ITG) and trapped electron mode (TEM) range. Nonlinear GYRO simulations have also been performed and the predicted fluctuation is compared against experimental measurements through a synthetic PCI diagnostic method. Both L-Mode and H-Mode plasmas are examined through these numerical and experimental methods. The L-Mode experiments were carried out over the range of densities covering the "neo-Alcator" (linear confinement time scaling with density, electron transport dominates) to the "saturated ohmic" regime. The key role played by the ITG turbulence has been verified. In the saturated ohmic regime, the simulated ion and electron thermal diffusivities also agree with experiments after varying the ion temperature gradient within experimental uncertainty. However, in the linear ohmic regime, GYRO does not agree well with experiments, showing significantly larger ion thermal transport and smaller electron thermal transport.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Lin, Liang, Ph. D. Massachusetts Institute of Technology

Advisor dc:contributor.advisor

• Miklos Porkolab.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/53230

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/53230