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Observation of Sawtooth Oscillations in the COMPASS Tokamak
Imríšek, Martin ; Havlíček, Josef ; Weinzettl, Vladimír ; Mlynář, Jan
The sawtooth instability in tokamak plasmas results in periodic relaxations of the core plasma density and temperature. The physics of sawtooth is still not fully understood. It is predicted that fusion-born alpha particles will lead to long sawteeth. However, longer sawteeth can seed other instabilities which cause further degradation of plasma confinement. This paper provides brief introduction into sawtooth physics and observations of sawtooth instability in COMPASS. Furthermore, evidence of triggering transition to high confinement regime by sawtooth crash is presented
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Diagnostic Lithium Beam System for COMPASS Tokamak
Háček, P. ; Weinzettl, Vladimír ; Stöckel, Jan ; Anda, G. ; Veres, G. ; Zoletnik, S. ; Berta, M.
The COMPASS tokamak has been re-installed in IPP Prague after its transport from Culham in UK. A Diagnostic Lithium Beam system is being developed for COMPASS tokamak. Its main goal is to provide edge density (Beam Emission Spectroscopy) and edge plasma current (Atomic Beam Probe) measurements to address the scientific programme focused on H-mode and pedestal physics. It features several newly designed and developed parts, including improved emitter and neutralizer. Atomic Beam Probe is an innovatory diagnostic for measurement of poloidal magnetic field and plasma current fluctuations in the plasma edge. Currently, the system is connected to tokamak (August 2011) and first experiments with plasma were performed. The system still undergoes vacuum, neutralization and high voltage testing. This article reviews the concept and current state of the Lithium Beam diagnostic for COMPASS and provides its first test results.
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Data Acquisition System and Data Processing for the New Thomson Scattering System on the COMPASS Tokamak
Aftanas, Milan ; Bílková, Petra ; Böhm, Petr ; Weinzettl, Vladimír ; Stöckel, Jan ; Hron, Martin ; Pánek, Radomír ; Scannell, R. ; Walsh, M.
The Thomson scattering (TS) will be one of crucial plasma diagnostics of the COMPASS tokamak. This newly build-up multi-point system consists of two Nd:YAG lasers (1.6J at 1064nm, 30Hz each) and cascade filter polychromators with avalanche photodiodes. It will enable measurements of both the electron temperature Te (20eV − 5000eV ) and density ne (1019 − 1020m−3) profiles with spatial resolution up to 3mm in the vertical direction in 56 spatial points. The uniquely designed complex data acquisition system based on fast analog digital convertors (1GS/s) reflects the need to retrieve/digitize the signal originated from scattering process of the laser pulse lasting less than 10ns. This paper presents a detailed review of the architecture of the control and the data acquisition (DAQ) system and its features. LabViewr will be used as a main layer for the TS data acquisition. Routines specifically written for controlling the DAQ of TS on COMPASS are presented.
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Atomic Beam Probe Diagnostic for COMPASS Tokamak
Háček, Pavel ; Weinzettl, Vladimír ; Stöckel, Jan ; Anda, G. ; Veres, G. ; Zoletnik, S. ; Berta, M.
The COMPASS tokamak has been re-installed in IPP Prague after its transport from Culham in UK. New diagnostic tools are under development to address the scientific program focused on H-mode and pedestal physics. Atomic Beam Probe (ABP) is an innovatory diagnostic for measurement of poloidal magnetic field and plasma current fluctuations in the plasma edge. It is planned to be an extension of the beam emission spectroscopy system by collecting the lithium ions stemming from beam ionization. In the first approximation, ionization is proportional to the local plasma density. The poloidal magnetic field moves the ions toroidally. Therefore, the two-dimensional poloidal-toroidal measurement of the ion current in the exit port reveals information on both the density and magnetic field profiles, thereby also on the edge current profile. This article reviews the concept of the ABP diagnostic and the status of its installation on the COMPASS tokamak.
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Measurement of the Laser Beam Position and Width for the Thomson Scattering Diagnostics on Tokamak COMPASS
Aftanas, Milan ; Bílková, Petra ; Böhm, Petr ; Weinzettl, Vladimír ; Stöckel, Jan ; Hron, Martin ; Pánek, Radomír
COMPASS tokamak is equipped with new key diagnostic—Thomson scattering system. This unique multi-point system has been designed with the main aim to investigate electron density and temperature profiles on the COMPASS tokamak (R = 0.56 m, a = 0.18 m, BT max = 2.1 T). The spatial resolution is optimized namely for the pedestal studies (radial spatial resolution a/100). This contribution describes particular steps of optical alignment of the important part of the Thomson scattering system, Nd:YAG lasers (1.6 J at 1064 nm, 30 Hz). Laser beam width has to be precisely measured and laser beam position has to be precisely set before the measurement and checked for all laser shots to be able of decrypting the information about the plasma density and also to improve precision of the measurement. New tool for automatic measurement of the laser beam misalignment is introduced.
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Measurements of Ion Temperature in the Edge Plasma of the COMPASS Tokamak
Naydenkova, Diana ; Janky, Filip ; Weinzettl, Vladimír ; Stöckel, Jan ; Šesták, David ; Odstrčil, T. ; Ghosh, J. ; Gomes, R. ; Pereira, T.
The two-grating spectrometer, which has been developed for the ISTTOK tokamak, allows an estimation of the temporal evolution of both ion temperature and poloidal velocity of the edge plasma by analysis of Doppler-shifted and broadened CIII spectral lines at ~465nm. At the current phase of the COMPASS tokamak operation, the first measurements of ion temperature using the optical system based on the spectrometer were performed and first results are presented.
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Navrh filtru pro detekci Thomsonovym rozptylem na tokamaku COMPASS
Aftanas, Milan ; Scannell, R. ; Bílková, Petra ; Böhm, Petr ; Weinzettl, Vladimír ; Walsh, M.
Reinstalled tokamak COMPASS, originally from Culham Science Centre, is now operating at the Institute of Plasma Physics, Prague and many new optical diagnostics are being developed [Sestak et al, 2009]. For measurement of electron temperature and density profiles, high resolution incoherent Thomson scattering spectroscopy based on Nd:YAG laser and avalanche photodiodes is under development now. The paper outlines part of the design of this diagnostic - proper choice of spectral filters. The design of filters is shown and its evaluation taking into account different angle of scattered light is introduced. Error bars of the electron temperature, density and pressure are determined with respect to assumed electron temperature and density profiles and to required high spatial resolution at the pedestal region.
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