A motional stark effect instrument to measure q(R) on the C-mod tokamak
A motional Stark effect (MSE) instrument to measure q(r) using the Torus Experiment for Technology (TEXT) neutral beam on the Alcator C-Mod tokamak has been designed and installed. The neutral beam is on the midplane, aimed radially, and designed to operate in hydrogen at 50 keV. The MSE optics view the outer half of the plasma -0.3<(R-R{sub 0})/a<1.05. This geometry results in a spatial resolution of 1 (edge)--3 (center) cm from a beam apertured horizontally to 2 cm. Estimates of the signal levels indicate for H{alpha} that photoelectron statistical errors in the measurement of B{sub {theta}}/B{sub {phi}} can be less than 0.2% for n{sub e0}<2.0x10{sup 14} cm{sup -3} similar to other MSE instruments. The collection optics reside within the vacuum chamber reflecting and imaging the neutral beam through a vacuum window in the neutral beam port. The optics are designed so that beam emission spectroscopy can be carried out simultaneously with MSE measurements. Optical signals are transmitted to remote detectors by fiber optics. Low Verdet glass and dielectric mirrors are used to minimize polarization changes caused by the ambient fields. Polarization is measured by conventional techniques using photoelastic modulators, optical filters, and photomultipliers.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40204771
- Journal Information:
- Review of Scientific Instruments, Vol. 72, Issue 1; Other Information: Othernumber: RSINAK000072000001001012000001; 616101CON; PBD: Jan 2001; ISSN 0034-6748
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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Design of a new optical system for Alcator C-Mod motional Stark effect diagnostic
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