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Anomalous Diffusion of Electrons in Tokamak by Their Interaction With Lower Hybrid Wave
Seidl, Jakub ; Krlín, Ladislav (advisor) ; Rohlena, Karel (referee)
Interaction of electrons with a lower-hybrid wave (LHW) is usually described using a quasilinear theory. It was shown formerly that in some cases the quasilinear approach is not proper. This work deals with an eect of spatial geometry of LHW spectra on a particle velocity diusion. Diusion coecient for various cases was computed and put to use to predict a long term evolution of an electron velocity distribution function. The computation was (on the contrary of previous papers) based on fully relativistic equations of motion. The results conrm that region of high electron acceleration is broadest just after the wave enters plasma and becomes narrower along its progress deeper into it. In the range of wave intensities over 105 V/m we found that the diusion becomes Lévy-walk. In the second part predictions of electron acceleration in front of LH grill of two dierent approaches were compared. We showed that the approach based on usage of Fourier expansion of potential gives only a rough estimate of the acceleration.
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Study of Alfven Eigenmodes in Tokamak COMPASS
Markovič, Tomáš ; Stöckel, Jan ; Seidl, Jakub ; Melnikov, A. ; Medvedev, S.
Having both MHD and kinetic character plasma Alfven eigenmodes are signicant not only on the eld basic plasma research, but also on the eld of magnetic connement fusion. An introduction to basic physical principles of Alfven eigenmodes under MHD approximation is provided. Presented results of recent experiments on COMPASS suggest occurrence of toroidal Alfven eigenmodes in this tokamak, which is further supported by preliminary linear MHD code simulations, althought more studies will have to be conducted in the future to further investigate presented modes therein.
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First measurements with U-probe on the COMPASS tokamak
Kovařík, Karel ; Ďuran, Ivan ; Stöckel, Jan ; Seidl, Jakub ; Šesták, David ; Brotánková, J. ; Spolaore, M. ; Martines, E. ; Vianello, N.
A complex electrostatic-magnetic probe diagnostics, baptized as ‘U-probe’, has been installed on COMPASS tokamak recently. Probe composes of two identical towers. Each tower houses 3 radially spaced sets of 3D coils, triple probe and rake probe – array of six Langmuir probes. The U-probe measures electric and magnetic properties of the filamentary structures in the edge plasma, particularly the floating potential profile and local magnetic field within the plasma filaments. Contribution presents first tests and results obtained.
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U-probe for the COMPASS Tokamak
Kovařík, Karel ; Ďuran, Ivan ; Stöckel, Jan ; Seidl, Jakub ; Šesták, David ; Brotánková, J. ; Spolaore, M. ; Martines, E. ; Vianello, N. ; Hidalgo, C. ; Pedrosa, M. A.
A complex electrostatic-magnetic probe diagnostics, baptized as 'U-probe', is being prepared for measurement of properties of the filamentary structures in the edge plasmas of COMPASS tokamak. Probe will be composed of two identical towers. Each tower will house 3 sets of 3D coils, balanced triple probe and six single Langmuir probes each. The design of the probe is based on that of U-probe used on reversed field pinch RFX-mod and our combined electromagnetic probe at TJ-II stellarator. This new COMPASS diagnostic will measure vorticity and longitudial electric current of the plasma filaments. Analysis of the properties and, particularly, the correlation between filament vorticity and its current is expected to shed light into physics of filamentary structures in the tokamak plasma edge. The simulation of the probe surface temperature evolution as a function of expected incident heat loads within the COMPASS edge plasmas is presented.
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