Sub-millisecond electron density profile measurement at the JET tokamak with the fast lithium beam emission spectroscopy system

D. I. Réfy, M. Brix, R. Gomes, B. Tál, S. Zoletnik, D. Dunai, G. Kocsis, S. Kálvin, T. Szabolics

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Diagnostic alkali atom (e.g., lithium) beams are routinely used to diagnose magnetically confined plasmas, namely, to measure the plasma electron density profile in the edge and the scrape off layer region. A light splitting optics system was installed into the observation system of the lithium beam emission spectroscopy diagnostic at the Joint European Torus (JET) tokamak, which allows simultaneous measurement of the beam light emission with a spectrometer and a fast avalanche photodiode (APD) camera. The spectrometer measurement allows density profile reconstruction with ∼10 ms time resolution, absolute position calculation from the Doppler shift, spectral background subtraction as well as relative intensity calibration of the channels for each discharge. The APD system is capable of measuring light intensities on the microsecond time scale. However ∼100 μs integration is needed to have an acceptable signal to noise ratio due to moderate light levels. Fast modulation of the beam up to 30 kHz is implemented which allows background subtraction on the 100 μs time scale. The measurement covers the 0.9 < ρpol < 1.1 range with 6-10 mm optical resolution at the measurement location which translates to 3-5 mm radial resolution at the midplane due to flux expansion. An automated routine has been developed which performs the background subtraction, the relative calibration, and the comprehensive error calculation, runs a Bayesian density reconstruction code, and loads results to the JET database. The paper demonstrates the capability of the APD system by analyzing fast phenomena like pellet injection and edge localized modes.

Original languageEnglish
Article number043509
JournalReview of Scientific Instruments
Volume89
Issue number4
DOIs
Publication statusPublished - Apr 1 2018

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Electron density measurement
Joint European Torus
electron density profiles
Emission spectroscopy
Lithium
lithium
Avalanche photodiodes
subtraction
avalanches
photodiodes
spectroscopy
spectrometers
Spectrometers
Calibration
Plasmas
pellets
luminous intensity
Doppler effect
Light emission
light emission

ASJC Scopus subject areas

  • Instrumentation

Cite this

Sub-millisecond electron density profile measurement at the JET tokamak with the fast lithium beam emission spectroscopy system. / Réfy, D. I.; Brix, M.; Gomes, R.; Tál, B.; Zoletnik, S.; Dunai, D.; Kocsis, G.; Kálvin, S.; Szabolics, T.

In: Review of Scientific Instruments, Vol. 89, No. 4, 043509, 01.04.2018.

Research output: Contribution to journalArticle

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