93 research outputs found
Fast Ion Dynamics in ASDEX Upgrade and TEXTOR Measured by Collective Thomson Scattering
No full textFast ions are an essential ingredient in burning nuclear fusion plasmas: they are responsible for heating the bulk plasma, carry a significant amount of plasma current and moreover interact with various magnetohydrodynamic (MHD) instabilities. The collective Thomson scattering (CTS) diagnostic is sensitive to the projection of fast ion velocity distribution function. This thesis is mainly devoted to investigations of fast ion physics in tokamak plasmas by means of CTS
Bi-Maxwellian, slowing-down, and ring velocity distributions of fast ions in magnetized plasmas
No full textWe discuss analytical fast-ion velocity distribution functions which are useful for basic plasma modelling as illustrated for the tokamak ITER. The Maxwellian is by far the most widespread model for ions and electrons in tokamaks and stellarators. The bi-Maxwellian and the drifting (bi-)Maxwellian are extensions allowing for anisotropy and bulk plasma flow, respectively. For example, fast ions generated by wave heating in the ion cyclotron range of frequencies are often described by bi-Maxwellians or so-called tail temperatures. The ring distribution can serve as a basic building block for arbitrary distributions or as a bump-on-tail in stability studies. The isotropic slowing-down distribution is a good model for fusion α-particles. The anisotropic slowing-down distribution occurs for anisotropic particle sources as is typical for neutral beam injection. We physically motivate these distribution functions and present analytical models in various coordinate systems commonly used by theorists and experimentalists. We further calculate 1D projections of the distribution functions onto a diagnostic line-of-sight to gain insight into measurements relying on the Doppler shift
Development of the collective Thomson scattering diagnostic on Wendelstein 7-X: theory and application
No full textHow to improve plasma diagnostics on Wendelstein 7-X with Collective Thomson Scatterin
Investigation of fast-ion dynamics on ASDEX-Upgrade and TEXTOR using collective Thomson scattering
No full text3D particle tracking velocimetry using dynamic discrete tomography for plasma physics applications
No full text3D particle tracking velocimetry (PTV) is a diagnostic technique which is widely used for studying flows, combustion, and plasmas. Current tomographic particle tracking methods are based on the multiplicative algebraic reconstruction technique and used for reconstructing the distribution of multi-pixel sized particles as greylevel images. Reconstructions obtained by these methods do not necessarily match the experimental data. We propose a new algorithm which can be used for tracking dust particles in tokamaks and stellarators, as well as in low-temperature and complex plasmas. The dynamic discrete tomography algorithm is efficient for data from two projection directions and exact. The non-uniqueness can be detected and tracked individually. The algorithm performance is proportional to N3 on average where N is the number of particles in the reconstruction. There is a room for further improvement of the computational cost scaling. Information from previously reconstructed frames is incorporated in the reconstruction procedure that is formulated as a discrete optimization problem, which has not been applied in PTV previously
Invasive species Dreissena polymorpha in the Northern Dvina River estuary
No full textThe features of distribution of Dreissena polymorpha (Pallas, 1771) in the northeastern part of the range and in the estuary part of the Northern Dvina River are described. Based on the earlier studies of different authors, it was suggested that the population of this mollusk is independent and self-replicating. To prove that, our study provides some population characteristics of D. polymorpha settlements. Mollusk samples were taken in the summer in 2018-2021. The research was conducted in the upper delta and in the lower part of the estuary section in order to evaluate the agglomeration. In total, 1538 individuals were selected from three sites of collection. A set of morphometric measurements was performed. Intra-population diversity was studied, weight and length of D. polymorpha individuals were evaluated. Statistically significant differences were found between the individuals living in the upstream estuary and those living in the Northern Dvina River delta, which is explained by the differences caused by of abiotic factors such as current velocities, availability of suitable substrates, amount of nutrients. There were no significant differences in the presented parameters between the second and third sampling site, due to the relative proximity of the sampling stations. The importance of further study of the biology and ecology of this mollusk in the North Dvina River basin is shown
3D particle tracking velocimetry using dynamic discrete tomography
No full textParticle tracking velocimetry in 3D is becoming an increasingly important imaging tool in the study of fluid dynamics and combustion as well as plasmas. We introduce a dynamic discrete tomography algorithm for reconstructing particle trajectories from projections. The algorithm is efficient for data from two projection directions and exact in the sense that it finds a solution consistent with the experimental data. Non-uniqueness of solutions can be detected and solutions can be tracked individually
Recent progress in fast-ion diagnostics for magnetically confined plasmas
No full textOn the road to a fusion reactor, a thorough control of the fast-ion distribution plays a crucial role. Fusion-born α-particles are, indeed, a necessary ingredient of self-sustained burning plasmas. Recent developments in the diagnostic of fast-ion distributions have significantly improved our predictive capabilities towards future devices. Here, we review key diagnostic techniques for confined and lost fast ions in tokamak and stellarator plasmas. We discuss neutron and gamma-ray spectroscopy, fast-ion D-α spectroscopy, collective Thomson scattering, neutral particle analyzers, and fast-ion loss detectors. The review covers physical principles of each diagnostic, sensitivities, basic setups, and operational parameters. The review is largely (but not exclusively) based on the contributions from ASDEX Upgrade and JET. Finally, we discuss integrated data analysis of fast-ion diagnostics by velocity-space tomography which allows measurements of 2D velocity distribution functions of confined fast ions
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