||Visible light without spectral resolution, monitoring of plasma-surface interaction
||About 1 mm (full poloidal cross-section covered by 990x900 pixels)
1280x1024 px at 400 Hz, 32x1 px at about 100 kHz
Wigner Research Centre for Physics, Budapest, Hungary
“Event Detection Intelligent Camera” (EDICAM) is a fast video camera system developed for a diagnostic usage in plasma physical experiments. On COMPASS, the two identical EDICAM fast cameras have been installed to monitor plasma behaviour and plasma-surface interaction.
The camera system consists of the sensor module of EDICAM and the data acquisition computer (Fig. 1). A fully functional prototype of the camera mounted together with especially designed optics has been put in operation on the COMPASS tokamak in February 2009. Afterwards, the final version of the camera driven via fiber optics was successfully installed and tested in summer 2010. The EDICAM1 camera provides toroidal views on plasma discharges. The EDICAM2 camera has been used in a vertical direction for observations of the divertor region since 2012. In 2014, a new objective for toroidal observations provided a possibility to monitor the divertor region toroidally, and also to perform physical experiments using so called gas-puff imaging (method how to illuminate the edge plasma turbulence by a local puffing of the neutral gas).
Fig. 1: The EDICAM system - the camera mounted in the tangential port of COMPASS (left) and the driving PC together with power supply for the camera (right).
A typical camera frame resolution is 1280x1024 pixels at milliseconds time scales, however, the resolution can be decreased to reach extremely fast frame rates of 100 kHz, if required. After the discharge, camera pictures are automatically stored in both TIFF and JPG formats enabling later image post-processing.
The camera system observes the plasma column in a tangential direction and is routinely used to monitor plasma-wall interaction (Fig. 2). However, its speed also allows obtaining information on other plasma processes radiating in a visible light range (Fig. 3).
Fig. 2: Plasma-wall interaction seen by the fast camera during COMPASS tokamak discharges #310 (left) and #312 (right). Frames size is 800x600 pixels, exposition time is 0.6 ms.
Fig. 3: Formation of circular plasma at 6th ms in the discharge #323 and a dust particle tracking demonstrated on three consecutive camera frames of 800x600 pixels spaced in time by 1.475 ms.
Tokamak plasmas are optically thin for visible light radiation, and therefore radiation flux seen by individual pixels of the camera represents an integrated value along a corresponding chord (line-of-sight). Toroidally oriented field of view of the camera, i.e. along magnetic field lines, gains from the fact that most of visible radiation of high-temperature tokamak plasmas comes from relatively thin radiation shell located near the last closed flux surface, where a steep increase of both electron density and temperature causes recordable excitation of neutral and low-ionized working gas and impurities. Consequently, the camera can observe toroidally symmetric circular plasma as a ring-like structure close to the inner limiter (magnetic high field side), see Fig. 4 (left). Usually, camera chords (views) near outer limiter (magnetic low field side) are not parallel to the radiation shell there and only cross it not forming outer part of the ring shape. In diverted plasma, impurity inflow from material walls is significantly reduced resulting in image brightness drop except a region of divertor and its legs, see Fig. 4 (right).
Fig. 4: Circular (left) and diverted (right) plasma configurations in the shots #3203, and #3329 respectively.
The camera control software is based on the JAVA programming language providing both the user-friendly interface for manual data collection (Fig. 5), and the fully automatic storage interface integrated with the COMPASS database.
Fig. 5: User interface of the camera control system for manual data collection.
 V.Weinzettl, M.Imrisek, J.Havlicek, J.Mlynar, D.Naydenkova, P.Hacek, M.Hron, F.Janky, D.Sarychev, M.Berta, A.Bencze, T.Szabolics: "On Use of Semiconductor Detector Arrays on COMPASS Tokamak
", World Academy of Science, Engineering and Technology 71 (2012), 628-634; published also in conference proceedings of ICPP 2012: International Conference on Plasma Physics, Venice, Italy, 14th
 M.Odstrcil, J.Mlynar, V.Weinzettl, P.Hacek, M.Berta, T.Szabolics, A.Bencze: "Dust Observation in the COMPASS Tokamak Using Fast Camera", Proceedings of the 22nd Annual Conference of Doctoral Students – WDS 2013, pp. 73-79, Prague, 4th-7th June 2013, MATFYZPRESS, ISBN 978-80-7378-251-1
 A.Szappanos, M.Berta, M.Hron, R.Panek, J.Stockel, S.Tulipan, G.Veres, V.Weinzettl, S.Zoletnik: "EDICAM fast video Diagnostic installation on the COMPASS tokamak
", IAEA-TM2009/118, Fusion Engineering and Design 85 (2010) 370–373, doi:10.1016/j.fusengdes.2009.11.001