Filter Polychromators

Eight-Channel Polychromator

For over 25 years, General Atomics has been making Thomson scattering measurements of high temperature plasmas. With the development of repetitively pulsing Nd:YAG lasers and avalanche photodiode detectors (APDs), Thomson scattering measurements have evolved from single point, single time measurements to multipoint, high repetition (over 100 Hz) measurements.

A contributor to the success of these measurements is the development of a high performance, compact polychromator that is easy to align and maintain. These polychromators have excellent stray light rejection and independent channel response; required features for precise light measurements in noisy environments. Forty-four polychromators are used on the Thomson scattering diagnostic for the DIII-D tokamak producing spatial profiles of the plasma electron density (0.05 < n_e(10²⁰/m³) < 5) and temperature (0.02 < T_e(keV) < 20) at rates as high as 160 Hz. Although these polychromators have been optimized for Thomson scattering measurements with Nd:YAG lasers, General Atomics has the design tools and experience to optimize for other lasers and/or other applications using alternative interference filters and detectors.

APPLICATIONS

Thomson Scattering
Spectroscopy

FEATURES

High Transmission
Compact
Up To 8 Wavelength Channels
Silicon Avalanche Photodiode Detectors
Advanced Detector Electronics
Temperature Stabilized
Fiber Optically Coupled
High Stray Light Rejection
Easy and Stable Alignment
Flexible Filter Arrangement

PROVEN PERFORMANCE

44 units built, installed, operated on DIII-D at General Atomics
32 fabricated for University of Wisconsin for MST , Pegasus and HSX .
10 fabricated for SSPX at LLNL
8 fabricated for Alcator C-Mod at MIT

Contact: Dr. Tom Carlstrom, 858 455-3552