A multichannel visible spectroscopy system for the ITER-like W divertor on EAST

Abstract

To facilitate long-pulse high power operation, an ITER-like actively cooled tungsten (W) divertor was installed in Experimental Advanced Superconducting Tokamak (EAST) to replace the original upper graphite divertor in 2014. A dedicated multichannel visible spectroscopic diagnostic system has been accordingly developed for the characterization of the plasma and impurities in the W divertor. An array of 22 lines-of-sight (LOSs) provides a profile measurement of the light emitted from the plasma along upper outer divertor, and the other 17 vertical LOSs view the upper inner divertor, achieving a 13 mm poloidal resolution in both regions. The light emitted from the plasma is collected by a specially designed optical lens assembly and then transferred to a Czerny-Turner spectrometer via 40 m quartz fibers. At the end, the spectra dispersed by the spectrometer are recorded with an Electron-Multiplying Charge Coupled Device (EMCCD). The optical throughput and quantum efficiency of the system are optimized in the wavelength range 350-700 nm. The spectral resolution/coverage can be adjusted from 0.01 nm/3 nm to 0.41 nm/140 nm by switching the grating with suitable groove density. The frame rate depends on the setting of LOS number in EMCCD and can reach nearly 2 kHz for single LOS detection. The light collected by the front optical lens can also be divided and partly transferred to a photomultiplier tube array with specified bandpass filter, which can provide faster sampling rates by up to 200 kHz. The spectroscopic diagnostic is routinely operated in EAST discharges with absolute optical calibrations applied before and after each campaign, monitoring photon fluxes from impurities and H recycling in the upper divertor. This paper presents the technical details of the diagnostic and typical measurements during EAST discharges.

Effect of ∇B drift on the H-mode power threshold in upper single null plasmas with ITER-like tungsten divertor on EAST

“…The spectroscopic diagnostic for detecting the influx of impurity at the tungsten divertor region has been utilized. 24 The line emissions intensity of tungsten (W), oxygen (O), nitrogen (N), lithium (Li), and carbon (C), normalized to the D Balmer line (D d , 410.06 nm) measured by the divertor spectroscopy versus loss powers across the separatrix, P loss , are shown in Fig. 6, with respect to two field directions, which are averaged over a time interval of 10 ms in the Lmode phase just prior to the L-H transition.…”

Plasma–tungsten interactions in experimental advanced superconducting tokamak (EAST)

“…The measured radiances from excited neutral W atoms can, therefore, be converted into W atom fluxes from the targets. A multichannel spectroscopic system was built on EAST to dedicatedly measure the emission lines of impurities in the upper W divertor region [13]. This system has a vertical array of 22 LOSs directed at the outer target and 17 LOSs at the inner target, respectively, which provides profile measurements of W sources along both divertor targets with a 13 mm poloidal resolution ( Fig.…”

“…Two types of spectroscopic detecting systems are used for the Reproduced with permission from Ref. [13]. Copyright 2017 AIP Publishing analysis of the plasma emission light transmitted through fibers.…”

“…A large portion of EAST wall is covered with carbon (C) tiles, including the graphite lower divertor, neutral beam shinethrough region at the high field first wall and the guarder Reproduced with permission from Ref. [13]. Copyright 2017 AIP Publishing limiter for radio frequency heating antennas.…”

Electron density calculation based on Stark broadening of D Balmer line from detached plasma in EAST tungsten divertor

“…The collected light is transmitted via 40 m ultraviolet hard cladding silica optical fibers to a Czerny Turner spectrometer and then focused on an EM-CCD camera. A detailed description of this spectroscopic system is given in [12]. With vertical binning, a simultaneous measurement of 16 LOSs with temporal resolution of 5.3 ms can be achieved.…”