Title: A combined phase contrast imaging and heterodyne interferometer system for multiscale fluctuation measurements (invited)

Abstract

In this work, a novel combined diagnostic capable of measuring multiscale density fluctuations that extend from magnetohydrodynamic (MHD) to the lower range of electron temperature gradient turbulence has been designed, installed, and operated at DIII-D. The combined diagnostic was constructed by adding a heterodyne interferometer to the pre-existing phase contrast imaging (PCI) system, both of which measure line-integrated electron density fluctuations. The port-space footprint is minimized via use of a single 10.6 μm probe beam. With temporal bandwidths in excess of 1 MHz, the PCI measures high-k (1.5 cm^-1 < |k_R| ≤ 25 cm^-1) fluctuations with sensitivity 3×10¹³ m^-2/$$\sqrt{kHz}$$, while the interferometer simultaneously measures low-k (|k_R| < 5 cm^-1) fluctuations with sensitivity 3×10¹⁴ m^-2/$$\sqrt{kHz}$$. The intentional mid-k overlap has been empirically verified with sound-wave calibrations and allows quantitative investigation of multiscale effects that are predicted to be significant in the reactor-relevant T_e ~ T_i regime. Lastly, via correlation with the primary DIII-D interferometer, the toroidal mode numbers of core-localized MHD can be measured.

Authors:

Davis, E. M.  ^[1];

• Search DOE PAGES for author "Davis, E. M."
• Search DOE PAGES for ORCID "0000-0003-1039-6902"

Rost, J. C.  ^[1];

• Search DOE PAGES for author "Rost, J. C."
• Search DOE PAGES for ORCID "0000-0003-4501-8995"

Porkolab, M. ^[1]; Marinoni, A. ^[1]; Van Zeeland, M. A. ^[2]

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+ Show Author Affiliations

1. MIT Plasma Science and Fusion Center, Cambridge, MA (United States)
2. General Atomics, San Diego, CA (United States)

Publication Date:

Thu Jul 26 00:00:00 EDT 2018

Research Org.:

General Atomics, San Diego, CA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1609192

Alternate Identifier(s):

OSTI ID: 1461728

Grant/Contract Number:  

FC02-04ER54698; FC02-99ER54512; FG02-94ER54235; NA002135

Resource Type:

Accepted Manuscript

Journal Name:

Review of Scientific Instruments

Additional Journal Information:

Journal Volume: 89; Journal Issue: 10; Journal ID: ISSN 0034-6748

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; instruments & instrumentation; physics; interferometry; signal processing; plasma confinement; noise floor; multiscale methods; lasers; electron density; magnetohydrodynamics; turbulence measurement