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Experimentální studium centrální a okrajové oblasti prstence plazmatu na tokamaku Compass
Štefániková, Estera ; Tichý, Milan (vedoucí práce) ; Hron, Martin (oponent)
Diagnostika Thomsonova rozptylu s vysokým rozlišením na tokamaku COMPASS měří radiální profily elektronové teploty a hustoty v centrální a okrajové části plazmatu. Prostorové rozlišení v okrajové části je optimalizováno na studium okrajové transportní bariéry, která se formuje během módu s vyšším udržením (tzv. H-mod). Jsou pozorovány charakteristické krajové profily s tzv. pedestalem, o který se středový profil teploty a hustoty zvýší. Tvar pedestalu lze popsat funkcí modifikový hyperbolický tangens, což je pětiparametrový model, kterým se získají důležité parametry pedestalu jako např. výška a šírka. Nově je v této práci ukázáno fitování celých radiálních profilů elektronové teploty, hustoty a tlaku s pedestalem. Fitování se dál využije ve statistickém zpracování hodnot teploty a hustoty na vrcholu pedestalu, kdy chceme najít hranici tlaku oddělující režim H-modu.
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Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Seidl, Jakub ; Jiráková, Kateřina ; Adámek, Jiří ; Grover, Ondřej ; Horáček, Jan ; Hron, Martin ; Vondráček, Petr
We have identified two distinct types of turbulent fluctuations in COMPASS plasmas, the high-frequency edge oscillations and low-frequency SOL blobs. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of isat fluctuations is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL. This supports, together with turbulence spreading rate being positive in the near SOL but negative in the edge, the picture presented in [3] that most of the fluctuations that form a positive skewness in the edge region disappear around LCFS and new blobs are formed in the near SOL. Further, we cannot confirm the assumption that the blobs are generated randomly according to a Poisson process. Oscillations of all measured quantities, incl. radial particle flux, in the near SOL are peaked around ∼13 kHz. This seems to correspond to a poloidally rotating structure with a rather large poloidal wave-length ∼ 15 − 20 cm, that at least partly modulates blob generation. Nevertheless, we note that time separation of blobs becomes more random further in the SOL, possibly due to differences in their individual propagation. These observations hold for diverted plasmas, but the situation may be different in limited low-elongation plasmas where the radius of zero skewness was observed to be shifted significantly (several cm) inwards, compared to diverted configuration, and Gamma-like PDF is detected even inside the LCFS. Study of these plasmas is ongoing.
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Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Seidl, Jakub ; Jiráková, Kateřina ; Adámek, Jiří ; Grover, Ondřej ; Horáček, Jan ; Hron, Martin ; Vondráček, Petr
In this work we study properties of turbulent structures in the scrape-off layer (SOL) and edge plasma of the COMPASS tokamak. Two distinct types of coherent oscillations are observed: a) broadband high frequency branch rotating in the electron diamagnetic direction, appearing mainly in the confined region but protruding also to the SOL b) low-frequency blobs rotating in an opposite poloidal direction, formed in the vicinity of the radius of zero electric field. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of fluctuations of the ion saturation current is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL and most of the fluctuations that form a positive skewness in the edge region disappear around LCFS.
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RE beam generation in MGI disruptions on COMPASS.
Ficker, Ondřej ; Mlynář, Jan ; Macúšová, Eva ; Vlainić, M. ; Weinzettl, Vladimír ; Urban, Jakub ; Čeřovský, Jaroslav ; Farník, Michal ; Markovič, Tomáš ; Papřok, Richard ; Vondráček, Petr ; Imríšek, Martin ; Tomeš, Matěj ; Havlíček, Josef ; Varju, Jozef ; Varavin, Mykyta ; Bogár, Ondrej ; Havránek, Aleš ; Gospodarczyk, M. ; Rabinski, M. ; Jakubowski, M. ; Malinovski, K. ; Zebrowski, J. ; Plyusnin, V. ; Papp, G. ; Pánek, Radomír ; Hron, Martin
In the experiments with the massive gas injection (MGI) triggered disruptions in the COMPASS tokamak, post-disruptive runaway electron (RE) beams are generated occasionally. In this contribution, a relatively large set of discharges from the recent years is analysed in order to improve our understanding of the processes behind the beam generation. It seems that despite the low toroidal field applied in the discharges (typically 1.15 T) the magnetic perturbations may be small enough to allow the acceleration and confinement of the electrons. The influence of the different components and different sections of the frequency spectrum of the magnetic perturbations on the beam generation and RE beam current is examined. Fast visible camera images are also analysed. The relevance of COMPASS runaway electron experiments for large machines is discussed. Moreover, the potential of less common diagnostic tools (Cherenkov detector, vertical ECE, ...) to clarify the role of the pre-disruption fast electron population and the influence of prompt runaway electron losses in the current quench is discussed using the recent test measurements.
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Experimentální studium centrální a okrajové oblasti prstence plazmatu na tokamaku Compass
Štefániková, Estera ; Tichý, Milan (vedoucí práce) ; Hron, Martin (oponent)
Diagnostika Thomsonova rozptylu s vysokým rozlišením na tokamaku COMPASS měří radiální profily elektronové teploty a hustoty v centrální a okrajové části plazmatu. Prostorové rozlišení v okrajové části je optimalizováno na studium okrajové transportní bariéry, která se formuje během módu s vyšším udržením (tzv. H-mod). Jsou pozorovány charakteristické krajové profily s tzv. pedestalem, o který se středový profil teploty a hustoty zvýší. Tvar pedestalu lze popsat funkcí modifikový hyperbolický tangens, což je pětiparametrový model, kterým se získají důležité parametry pedestalu jako např. výška a šírka. Nově je v této práci ukázáno fitování celých radiálních profilů elektronové teploty, hustoty a tlaku s pedestalem. Fitování se dál využije ve statistickém zpracování hodnot teploty a hustoty na vrcholu pedestalu, kdy chceme najít hranici tlaku oddělující režim H-modu.
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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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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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Status of Magnetic Diagnostics on COMPASS
Havlíček, J. ; Kudláček, O. ; Janky, F. ; Horáček, Jan ; Beňo, R. ; Valcárcel, D.F. ; Fixa, J. ; Brotánková, Jana ; Zajac, Jaromír ; Hron, Martin ; Pánek, Radomír ; Cahyna, Pavel
The COMPASS tokamak is in a test operation after its reinstallation in Institute of Plasma Physics AS CR in Prague (IPP Prague) in the year 2008. This operation consists of commissioning of various diagnostics and tokamak auxiliary systems. This paper presents current status of magnetic diagnostics after its refurbishment, used method of the calibration and shows examples of magnetic diagnostics utilization for plasma position reconstruction as well as for vertical hydraulic preload interlock system.
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Kontrola vakua a plynového systému pro tokamak COMPASS
Janky, F. ; Pereira, T.V. ; Santos, B.A. ; Hron, Martin
Tato práce je zaměřená na vytvoření nové kontroly a ovládaní vakua a napouštěcího systému pro tokamak COMPASS po jeho reinstalaci. Je nevyhnutelné vybudovat systém tak, že bude neustále v provozu. Firmvér naprogramovaný v programovacím jazyku C, kontroluje zařízení zapojené na vakuum a napouštěcí systém. Firmvér je naprogramovaný na mikrokontroler dsPIC, který byl osazený na desce v IST Lisabon. Vakuum a napouštěcí systém jsou připojené optickými kabely na server a můžou být vzdáleně ovládané z pracovní stanice umístěné v ovládací místnosti.
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