Progress of development of Thomson scattering diagnostic system on COMPASS

Abstract

A new Thomson scattering diagnostic system has been designed and is being built now on the COMPASS tokamak at the Institute of Plasma Physics ASCR in Prague (IPP Prague) in the Czech Republic. This contribution focuses on design, development, and installation of the light collection and detection system. High spatial resolution of 3 mm will be achieved by a combination of design of collection optics and connected polychromators. Imaging characteristics of both core and edge plasma collection objectives are described and fiber backplane design is presented. Several calibration procedures are discussed. The operational deployment of the Thomson scattering diagnostic is planned by the end of 2010.

High-resolution Thomson scattering system on the COMPASS tokamak: Evaluation of plasma parameters and error analysis

“…The scattered light from both regions is collected by custom designed objectives and relayed by fibre bundles out of the tokamak area into 29 polychromators. 5 Each of these polychromators divide the light into five spectral channels (using a set of filters), and light from each of these channels is then imaged onto an avalanche photodiode, where it is converted to an electrical signal. From each polychromator four of the five spectral channels are digitized; channels are chosen according to expected electron temperature range at corresponding spatial point.…”

“…11 The error σ S of the integral is calculated as a composite of Poisson, plasma light, and amplifier noise error. 12 The Poisson contribution can be determined from Raman scattering calibration 5 and it is given by σ Poisson 2 = F Raman × S high_pass_filter . Plasma light contribution can be estimated in the similar way from the S low_pass_filter integral over time of the laser pulse (let us say ±2σ of the pulse width) or it can be determined together with amplifier noise as a signal oscillations variance σ noise outside of the scattered pulse region (when no scattered signal is present).…”

Edge Thomson scattering diagnostic on COMPASS tokamak: Installation, calibration, operation, improvements

“…The polychromators are identical in both core and edge TS, with the same set of the spectral filters. 6 An example of electron temperature and density profiles during a standard tokamak discharge, obtained with both core and edge TS, is shown in Fig. 2 was D-shaped, with toroidal field 1.15 T and plasma current 160 kA, without an additional heating.…”

“…The second method can be used for initial alignment (during Raman calibration) and as a continuous feedback during standard TS measurements. So called "split-fibres" 6 are used for the purpose. It is a standard fibre bundle, but divided into halves along the laser chord.…”

Thomson scattering on COMPASS — commissioning and first data

“…Collection optics has been designed in IPP AS CR, v.v.i. [4]. Optical fibres have been designed to match well with parameters of collection lenses as well as with parameters 2012 JINST 7 C01074 of the laser beam [2].…”