Applying the new gamma ray imager diagnostic to measurements of runaway electron Bremsstrahlung radiation in the DIII-D Tokamak (invited)

C. M. Cooper, D. C. Pace, C. Paz-Soldan, N. Commaux, N. W. Eidietis, E. M. Hollmann, D. Shiraki

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

A new gamma ray imager (GRI) is developed to probe the electron distribution function with 2D spatial resolution during runaway electron (RE) experiments at the DIII-D tokamak. The diagnostic is sensitive to 0.5-100 MeV gamma rays, allowing characterization of the RE distribution function evolution during RE growth and dissipation. The GRI consists of a lead "pinhole camera" mounted on the DIII-D midplane with 123 honeycombed tangential chords 20 cm wide that span the vessel interior. Up to 30 bismuth germanate (BGO) scintillation detectors capture RE bremsstrahlung radiation for Pulse Height Analysis (PHA) capable of discriminating up to 20 000 pulses per second. Digital signal processing routines combining shaping filters are performed during PHA to reject noise and record gamma ray energy. The GRI setup and PHA algorithms will be described and initial data from experiments will be presented. A synthetic diagnostic is developed to generate the gamma ray spectrum of a GRI channel given the plasma information and a prescribed distribution function. Magnetic reconstructions of the plasma are used to calculate the angle between every GRI sightline and orient and discriminate gamma rays emitted by a field-aligned RE distribution function.

Original languageEnglish
Article number11E602
JournalReview of Scientific Instruments
Volume87
Issue number11
DOIs
StatePublished - Nov 1 2016

Funding

The authors would like to thank Vasily Kiptily, Rita Costa Pereira, and Ana Fernandes for valuable discussions and assistance in implementing the pulse height analysis methods; and Paul Schotanus and his colleagues at SCIONIX for their rapid support throughout the commissioning of the GRI. The GRI was designed and fabricated under General Atomics Internal Research and Development support. Testing of the camera on DIII-D was supported in part by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award Nos. DE-FC02-04ER54698, DE-AC05-06OR23100, and DE-FG02-07ER54912.

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