|
|
Multi-band Whistler-mode Chorus Emissions Observed by the Cluster Spacecraft
Macúšová, Eva ; Santolík, Ondřej
Whistler-mode chorus emissions are one of the most significant mechanisms causing the acceleration of electrons in the outer Van Allen radiation belt to relativistic energies. They consist of individual wave packets divided into two frequency bands separated close to the source region by a gap at 1/2 of the electron cyclotron frequency (fce). This configuration is called banded chorus and it is correlated with magnetic activity. Landau damping is one of the possible explanations describing the existence of the gap. On the other hand, the role of ducts in its formation was also discussed. We present several events of chorus combined with noisy or shapeless chorus-like emissions that are arranged in three or more frequency bands with two or more gaps and are observed mostly in a magnetic latitude range from 3 to 10 degrees on the both sides of the equator. We investigate possible influences of the magnetic local time (MLT), the Kp index, the McIlwain parameter and the plasma density on the formation of these multi-band emissions.
|
|
| |
|
|
Dynamics of cavitation induced by focused tandem shock waves in water
Hoffer, Petr ; Šunka, Pavel ; Lukeš, Petr
Cavitation associated with the generation of shock waves in water was examined. To study these processes, a tandem shock wave generator, which generates two cylindrical pressure waves focused by a metallic parabolic reflector to a common focal region, was developed. The temporal evolution of cavitation generated by shock waves at the focal region was determined experimentally using high-temporal-resolution microphotography for a certain time delay between the first and second shock waves. Observation of the focal area also showed jetting cavitation bubbles with diameters of 100 m without presence of any rigid boundary. A theoretical model that provides analytical expressions for the temporal evolution of the pressure inside the cavitation bubbles and parameters of the pressure waveform of the second shock wave at the focal area was used to improve the same measurement by PVDF sensor gauges. On the basis of this model, the amplitudes of the compression and rarefaction parts
|
|
|
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.
|
|
|
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.
|
|
|
Electrostatic assembly of alumina nanoparticles on nanocrystalline diamond films
Verveniotis, Elisseos ; Kromka, Alexander ; Rezek, Bohuslav
We apply atomic force microscope for local electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon, to induce electrostatically driven self-assembly of colloidal alumina nanoparticles into micro-patterns. The NCD films have sub-100 nm thickness and 60% relative sp2 phase content. We characterize charge contrast and stability in air, fluorocarbon oil and water by Kelvin force microscopy. We discuss factors influencing the charging process and demonstrate that the contrast of more than ± 1 V is needed to induce selfassembly of the nanoparticles via coulombic and polarization forces.
|
|
| |
|
|
Scaling Analysis Applied to Ionospheric, Solar and Geomagnetic Data
Mošna, Zbyšek ; Koucká Knížová, Petra
Scaling analysis based on structure function zeta(q) computed using wavelet analysis and spectrum D(h) is used to study possible connection of ionospheric system with the solar and geomagnetic activity. Data from six ionospheric stations (critical frequency foF2), solar flux F10.7 and geomagnetic indices AE, Kp and Dst are used. Data of foF2 show scale invariance in the period range 2–32 day. Scaling properties of ionospheric data show strong dependence on geomagnetic latitude of the station. Similar distribution of values of scaling exponents h for ionospheric and geomagnetic activity AE and Kp suggests connection between these systems. Values of h for foF2 and F10.7 have different distribution which suggests weak connection between these systems at chosen periods.
|
|
|
Influence of Non-vertical Echoes to Ionogram Scaling
Kouba, Daniel ; Koucká Knížová, Petra
Digisonde DPS 4 replaced the older ionosonde IPS 42 KEL Aerospace in the Observatory Pruhonice in January 2004. Additional information about the wave polarization enables us to determine and to distinguish exactly between ordinary and extraordinary wave traces on the ionogram records. This new ability basically changes scaling of the ionograms comparing to the ionograms obtained by classical ionosondes. Digisonde measurements show that in some cases the interpretation of ionograms based on classical ionospheric soundings may lead to the systematic errors, which affect classical ionograms interpretation. We demonstrate possible significant misinterpretations of the ionograms obtained using the classical equipment that is not able to distinguish between ordinary and extraordinary modes and records only time of flight of the electromagnetic sounding pulse. We show the necessity to be careful in using an old ionosonde measurements and scaled data for further analysis.
|
|
|
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.
|
guest ::
