title: CO2 laser polarimeter for Faraday rotation measurements in the DIII-D tokamak.
abstract: A tangential viewing, 10.59 microm CO(2) laser polarimeter for electron density measurements based on plasma induced Faraday rotation has been installed on DIII-D. The system uses colinear right- and left-hand circularly polarized beams with a difference frequency of 40 MHz to generate the necessary signal for heterodyne phase detection. The high-resolution phase information required to adequately resolve degree level polarization rotation is obtained using an all-digital "real-time" phase demodulation scheme based on modern digital signal processing techniques. Initial application of the system to DIII-D disruption mitigation experiments utilizing "massive gas jet" injection exhibits reliable operation and excellent agreement with CO(2) interferometer measurements; interestingly, the obtained Faraday rotation angles are in the range of those expected in ITER plasmas.
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Van Zeeland
authors.forename: R L
authors.initials: RL
authors.lastname: Boivin
authors.forename: T N
authors.initials: TN
authors.lastname: Carlstrom
authors.forename: T M
authors.initials: TM
authors.lastname: Deterly