Design of new Thomson scattering diagnostic system on COMPASS tokamak

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

“…Light collected in 30 spatial points is transferred through fibre bundles into 16 polychromators. 4 Number of spatial points is higher than number of polychromators thanks to duplexing technique-two adjacent fibre bundles are coupled into one polychromator, they are distinguished by different time of arrival of scattered light, because of fibre bundle length difference (20 m vs. 33 m). Two of the spatial points are used as split-fibre for alignment (see below).…”

“…3 The high resolution multi-point Thomson scattering (TS) diagnostic has been designed to provide the electron temperature and density profiles on the COMPASS tokamak. 4 The diagnostic consists of two sub-systems, observing core and edge plasma region. Commissioning of the core system was described earlier, including its relative (i.e., spectral) and absolute (i.e., Raman) calibration.…”

Overview of the COMPASS diagnostics

“…Light from particular spectral channels is detected by means of avalanche photodiodes with enhanced sensitivity in the infrared region. The design of fibre bundles ensures both optimal use of polychromator etendue (and thus good light collection) and sufficient insensitivity of the whole TS system to a possible laser misalignment [11]. Signals from all avalanche photodiodes (120 spectral channels) are processed by slow and fast analog-digital converters (ADCs) with very precise synchronization (inter-channel skew < 300 ps).…”

Progress of development of Thomson scattering diagnostic system on COMPASS

“…3 At the collection cell end, the cross-section of fiber bundle is a rectangle while at the polychromator end fibers form a circle of 3 mm diameter. The fibers are hexagonally close packed in bundles.…”