Národní úložiště šedé literatury Nalezeno 5 záznamů.  Hledání trvalo 0.01 vteřin. 
Study of instabilities in tokamak plasmas using radiation diagnostics
Imríšek, Martin ; Tichý, Milan (vedoucí práce) ; Igochine, Valentin (oponent) ; Jardin, Axel (oponent)
Název: Study of instabilities in tokamak plasmas using radiation diagnostics Autor: Martin Imríšek Katedra: Katedra fyziky povrchů a plazmatu Vedoucí: Prof. RNDr. Milan Tichý, DrSc. Konzultanti: Mgr. Vladimír Weinzettl, PhD. RNDr. Jan Mlynář, PhD. Abstract: Práce se zaměřuje na charakteriyaci pilovou nestabilitz a jejího vlivu na vybrané plasmové procesy na tokamaku COMPASS. Pád pilové nestability na tokamaku COMPASS předchází dominantní většíně L-H přechodů, sníženému výskutu nestability ELM a přechodům do H-modu v režimu bez nestabilitz ELM. Pilová nestabilita má také vliv na H-L přechod, který nastváv se yvýšenou pravděpodobností zhruba uprostřed jejího cyklu. Práce se také věnuje tomo- grafické rekonstrukci elektromagnetického zaření na tokamaku COMPASS a JET včetně aplikace optimalizovaných algoritmů ke studiu nestabilit v tokamakovém plasmatu a testování rychlých tomografických metod s možným využitím k řízení plasmatu. Práce také obsahuje simulace magnetických polí, které hrají důležitou roli ve stabilitě plasmatu a ve výpočtu tomografických rekonstrukcí. Tyto simu- lace byly také využity pro optimalizaci designu cívek tokamaku COMPASS-U. Klíčová slova: tokamak, tomografie, pilová nestabilita, electromagnetické...
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.
Global Power Balance in Non-Stationary Discharge Phases in the COMPASS Tokamak
Havlíček, Josef ; Imríšek, Martin ; Kovařík, Karel ; Weinzettl, Vladimír
The global power balance between different input power and sink/loss channels is important for understanding of tokamak physics, particularly for various scaling laws. The power balance is measured easily during stationary discharge phases because the terms for both magnetic field energy and plasma thermal energy build-up can be neglected. However, many important events in tokamak plasmas occur during non-stationary phases of the discharge. This article describes, quantifies and discusses the terms of the global power balance, including time dependent parts, and exemplifies them on the typical ohmic discharge of the COMPASS tokamak.
Absolute Sensitivity Calibration of Visible Spectroscopic Diagnostic and Temporal Evolution of First Window Transmittance at the COMPASS Tokamak
Naydenkova, Diana ; Weinzettl, Vladimír ; Stöckel, Jan ; Háček, Pavel ; Imríšek, Martin
An absolute calibration of spectroscopic systems is required to measure many important plasma parameters in tokamak discharges like impurity inflow, recycling and the effective ion charge. The procedure of the absolute calibration is described and technical issues and experimental limitations connected with the tokamak operation are discussed here. Namely, an influence of the first window transmittance and its evolution over experimental campaigns on the validity of the absolute calibration is investigated
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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