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Observation and Prediction of Runaway Electrons in the COMPASS Tokamak
Papřok, R. ; Krlín, Ladislav ; Stöckel, Jan
In this paper we present new measurements of HXR radiation from the COMPASS tokamak by the use of scintillation detector, 21-pinhole CdTe semiconductor detector. This radiation is caused by the presence of highly energetic runaway electrons and in the case of Neutral Beam Injection by fusion products. We also present direct runaway electrons measurements by Cherenkov detector. We present a theoretical prediction of runaway production based on theoretical formula and experimental data from Thomson scattering and compare it with a simpler experimental method based on peak counting.
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Simulations of Runaway Electrons
Papřok, R. ; Krlín, Ladislav ; Cahyna, Pavel
In this paper we discuss current knowledge of phenomena of runaway electrons in tokamaks. We summarize experimental facts and investigate theoretical understanding of runaway electrons. We also present result of our recent work concerning influence of JET’s Error Filed Correction Coils on runaway electrons dynamics. At the end of our paper we describe our plan to study runaway electrons dynamic in time and space varying magnetic field during plasma disruption as obtained from global MHD code JOREK.
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Impurity Dynamics in Turbulent Plasma in Tokamak Scrape-off Layer
Seidl, J. ; Krlín, Ladislav
We simulate behavior of plasma impurities in turbulent potential in tokamak scrape-off layer. Assuming low density of impurities we use test particle approach to investigate movement of individual particles in time evolving potential of isolated structure generated by interchange instability. Behavior of the plasma is modeled using reduced fluid model. We compare behavior of test particles under guiding center drift approximation with full-orbit 2D Hamiltonian equations of motion. While we find flow of particles governed purely by ExB drift to be incompressible, including also polarization drift results in compressibility of the flow. Particles traced along their full orbits exhibit the compressibility as well, however, larger in space and different in its amplitude. We therefore conclude that neglecting finite Larmor radius and assuming dynamics based on drift approximation may introduce significant error into simulations of impurity behavior in tokamak SOL.
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Bellanova nestabilita u nečistot zachycených v turbulentních strukturách v okrajové vrstvě tokamaku
Seidl, J. ; Krlín, Ladislav
We present description of an electrostatic turbulent model ESEL and explain interchange mechanism leading to turbulence generation in tokamak scrape-off layer. After introducing theory of Bellan instability, threshold for particle detrapping from turbulent structures (blobs) due to their finite Larmor orbits is discussed for the case of turbulence simulated by the ESEL model. Since plasma potential as well as floating potential are available from the simulation, it is possible to evaluate error made by using experimentally obtained floating potential in simulations of particle diffusion. It is shown that due to bipolar nature of blobs the outflow of particles from the blob caused by Bellan instability can be, in certain conditions, asymmetric and localized mainly into its upper and inner boundary.
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Pohyb nabitých částic v perturbovaných magnetických polích tokamaku
Papřok, R. ; Krlín, Ladislav ; Cahyna, Pavel ; Riccardo, V.
In this paper we present two Hamiltonian approaches–full and drift–for description of charged particles (e.g. electrons, D+) in magnetic field of a tokamak. We use a basic magnetic toroidal field configuration with shear plus overlapping island chains creating magnetic ergodic layer. We would like to use this apparatus for solving two physical problems. Firstly for an estimate of generation of electric field in edge plasma caused by addition of “ergodic coils”, which could serve as a mechanism for mitigation of ELMs and is will be studied on the COMPASS tokamak. Secondly we want to use the apparatus for tracing the influence on runaway electrons (energy 10 MeV) in the presence of magnetic field generated by Error Field Correction Coils (EFCCs) as are installed on JET Tokamak.
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