Design of a New Optical System for Alcator C-Mod Motional Stark Effect Diagnostic

[摘要] The motional Stark effect (MSE) diagnostic on Alcator C-Mod uses an in-vessel optical system (five lenses and three mirrors) to relay polarized light to an external polarimeter because port access limitations on Alcator C-Mod preclude a direct view of the diagnostic beam. The system experiences unacceptable, spurious drifts of order several degrees in measured pitch angle over the course of a run day. Recent experiments illuminated the MSE diagnostic with polarized light of fixed orientation as heat was applied to various optical elements. A large change in measured angle was observed as two particular lenses were heated, indicating that thermal-stress-induced birefringence is a likely cause of the spurious variability. Several new optical designs have been evaluated to eliminate the affected in-vessel lenses and to replace the focusing they provide with curved mirrors; however, ray tracing calculations imply that this method is not feasible. A new approach is under consideration that utilizes in situ calibrations with in-vessel reference polarized light sources. 2008 American Institute of Physics.

[发布日期] 2009-11-12

[学科分类] 原子、分子光学和等离子物理

[关键词] BIREFRINGENCE;DESIGN;FOCUSING;INCLINATION;LENSES;LIGHT SOURCES;MIRRORS;OPTICAL SYSTEMS;ORIENTATION;PHYSICS;POLARIMETERS;STARK EFFECT Diagnostic