Lower hybrid modeling and experiments on Alcator C-Mod

A highly flexible phase control system was developed in order to dynamically adjust the parallel wave number spectrum of driven LH waves on Alcator C-Mod. Wave coupling between the antenna and the plasma was studied using this system. A coupling code was modified to allow arbitrary phase and amplitude in each waveguide, which was required for agreement between the theory and experiment. Remarkable agreement was achieved when a small vacuum gap of 0.6 to 1.4 mm was included in the model, similar to results obtained on ASDEX. The location of the fast electron population is critical in diagnosing the performance of the lower hybrid system and can be inferred by measuring nonthermal bremsstrahlung emission. A state-of-the-art diagnostic for hard x-ray (HXR) emission was designed and used to make measurements of fast electrons bremsstrahlung during LHCD experiments on C-Mod. The HXR diagnostic consists of an array of 32 CdZnTe detectors to image energies in the 20-200 keV range. Detectors and pulse processing electronics were integrated into a compact and modular package. The system also makes use of fast digitization and software signal processing techniques allowing a maximum counting rate of 1 MHz. HXR experimental results indicate a spatially broad and centered fast electron population. HXR profiles predicted by a synthetic diagnostic in the Fokker-Planck code CQL3D are narrower than the observed profiles, suggesting the importance of spatial diffusion of fast electrons in the experiment. Lower hybrid experiments on C-Mod represent the first results obtained with density, magnetic field, plasma shape, and source frequency all near conditions expected on ITER. In initial experiments, about 400 kW of LH power was coupled for 400 ms into low density L-mode discharges.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Nuclear Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Liptac, John E

Advisor dc:contributor.advisor

• Ronald R. Parker.

• Nuclear Science and Engineering.

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/1721.1/41281

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/41281