Design and operation of the multipulse Thomson scattering diagnostic on DIII-D (invited)

Abstract

This paper describes the design and operation of a 40 spatial channel Thomson scattering system that uses multiple 20-Hz Nd:YAG lasers to measure the electron temperature and density profiles periodically throughout an entire plasma discharge. As many as eight lasers may be fired alternately for an average measurement frequency of 160 Hz, or they may be fired in rapid succession (<10 kHz), producing a burst of pulses for measuring transient events. The high spatial resolution (1.3 cm) and wide dynamic range (10 eV–20 keV) enable this system to resolve large electron density and temperature gradients formed at the plasma edge and in the scrape-off layer during H-mode operation. These features provide a formidable tool for studying L–H transitions, edge localized modes (ELMs), beta limits, transport, and disruptions in an efficient manner suitable for large tokamak operation where shot-to-shot scans are impractical. The scattered light is dispersed by interference filter polychromators and detected by silicon avalanche photodiodes. Laser control and data acquisition are performed in real time by a VME-based microcomputer. Data analysis is performed by a MicroVAX 3400. Additional features of this system include real-time analysis capability, full statistical treatment of error bars based on the measured background light, and laser beam quality and alignment monitoring during plasma operation. Results of component testing, calibration, plasma operation, and error analysis are presented.

Transport by intermittent convection in the boundary of the DIII-D tokamak

“…27,28 The Thomson scattering diagnostic at DIII-D 29 probes the plasma for 25 ns every 12 ms, clearly insufficient to properly sample the intermittency but sufficient to provide a rough comparison to the probe data. Thomson scattering density and temperature data accumulated for 500 ms in an L-mode discharge ͑to avoid the complication of ELMS͒ and superimposed over the average are shown in Figs.…”

Central flattening of the fast-ion profile in reversed-shear DIII-D discharges

“…At the magnetic axis, the peak of the fast-ion distribution function occurs at a pitch of v /v = 0.68, so an appreciable fraction of the fastion distribution can resonate with a TAE at v = v A /3 [9,10]. Figure 3 shows representative electron temperature profiles from Thomson scattering [11] and electron cyclotron emission (ECE) [12] diagnostics, electron density from Thomson scattering and CO 2 interferometry [13], and ion temperature, toroidal rotation, and carbon density profiles from chargeexchange recombination spectroscopy [14]. The dominant impurity is carbon in these discharges and Z eff 1.3.…”

Scrape-off layer transport and deposition studies in DIII-D

“…Plasma parameters and emission profiles were measured in the main chamber and divertor SOL with several diagnostics: electron densities and temperatures with Thomson scattering [Carlstrom_RSI92,Carlstrom_RSI97] and Langmuir probes [Watkins_RSI92,Watkins_JNM97], target heat flux with a vertical viewing infra-red camera [Lasnier_NF98], and line emission in the visible wavelength range with a multi-chord line-filtered spectral monitor system [Colchin_RSI03], and a multi-chord spectrometer [Brooks_RSI92]. Plasma imaging using toroidally viewing cameras [Fenstermacher_RSI97,Groth_RSI03] yielded 2-D emission profiles of hydrogen and low charge state carbon in the divertor and inner midplane.…”