Current profile measurements using MSE on Alcator C-Mod

A Motional Stark Effect (MSE) diagnostic system has been installed on the Alcator C-Mod tokamak to measure the plasma internal magnetic pitch angle profile. The diagnostic utilizes polarization patterns from Doppler-shifted Balmer-alpha decay emission from an energetic neutral beam injected into a magnetically confined plasma. This dissertation consists of three parts: (1) the current status of the C-Mod MSE diagnostic which includes major upgrades in the hardware and calibration techniques; (2) the elimination of the spurious drift in the polarization measurements due to thermal-stress induced birefringence; and (3) the measurement of current density profiles in Lower Hybrid Current Drive (LHCD) experiments. The major hardware upgrades include replacement of photomultiplier tubes (PMT's) with avalanche photodiodes (APD's) which enhanced the quantum efficiency; installation of a wire-grid polarizer to verify small Faraday rotation in the diagnostic; installation of steep edge filters to minimize pollution by the thermal Balmer-alpha signals; rotation of the Diagnostic Neutral Beam (DNB) which significantly reduced the anomalous effect from the secondary beam neutrals during the beam-into-gas calibrations. The new calibration techniques include two plasma calibrations: plasma current sweeping and the plasma size sweeping whose feasibility was experimentally proven; and an absolute intensity calibration which measured the real optical throughput of the system. A large database study indicates the signal-to-background ratio larger than 100 is required to have the measurement uncertainty under 0.1 degrees.

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

2009

Author dc:creator

• Ko, Jin-Seok

Advisor dc:contributor.advisor

• Steven D. Scott and Ian H. Hutchinson.

• 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/1721.1/53273

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/53273