A heterodyne dispersion interferometer for wide bandwidth density measurements on DIII-D

T Akiyama; M A Van Zeeland; R L Boivin; T N Carlstrom; J A Chavez; C M Muscatello; R O'Neill; J Vasquez; M Watkins; W Martin; A Colio; D K Finkenthal; D L Brower; J Chen; W X Ding; M Perry

doi:10.1063/1.5037997

A heterodyne dispersion interferometer for wide bandwidth density measurements on DIII-D

Rev Sci Instrum. 2018 Oct;89(10):10B105. doi: 10.1063/1.5037997.

Authors

T Akiyama¹, M A Van Zeeland², R L Boivin², T N Carlstrom², J A Chavez², C M Muscatello², R O'Neill², J Vasquez², M Watkins², W Martin², A Colio³, D K Finkenthal³, D L Brower⁴, J Chen⁴, W X Ding⁴, M Perry⁵

Affiliations

¹ National Institute for Fusion Science, 322-6 Oroshi-cho, Toki-shi, Gifu 509-5292, Japan.
² General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
³ Palomar College, San Marcos, California 92069, USA.
⁴ University of California, Los Angeles, Los Angeles, California 90095, USA.
⁵ California State University San Marcos, San Marcos, California 92096, USA.

PMID: 30399752
DOI: 10.1063/1.5037997

Abstract

In order to improve both the density and particularly the temporal resolution beyond previous dispersion interferometers (DIs), a heterodyne technique based on an acousto-optic (AO) cell has been added to the DI. A 40 MHz drive frequency for the AO cell allows density fluctuation measurements into the MHz range. A CO₂ laser-based heterodyne DI (HDI) installed on DIII-D has demonstrated that the HDI is capable of tracking the density evolution throughout DIII-D discharges, including disruption events and other rapid transient phenomena. The data also show good agreement with independent density measurements obtained with the existing DIII-D two-color interferometer. The HDI line-integrated density resolution sampled over a 1 s interval is ∼9 × 10¹⁷ m^-2. Density fluctuations induced by MHD instabilities are also successfully measured by the HDI.