Electro-Magneto-Hydrodynamic Model for Electron Microscopy

Táto dizertačná práca sa zaoberá popisom a tvorbou elektro-magnetohydrodynamického modelu určeného pre elektrónovú mikroskopiu. Základom práce je popis charakteristických javov prebiehajúcich v elektrónových mikroskopoch so zameraním na environmentálnu elektrónovú mikroskopiu. Práca sa zaoberala popisom elektromagnetického poľa, nadzvukového prúdenia zriedeného plynu a pohybu relativistických nabitých častíc v plynnom prostredí. Bol predstavený elektromagnetický model založený na definícii elektrického a magnetického vektorového potenciálu, ktorý bol využitý na simuláciu elektromagnetickej cievky. Nadzvukové prúdenie zriedeného plynu bolo sledované s využitím Navier- Stokesových rovníc. Pre rozšírenie ich aplikácie do nízkeho tlaku boli upravené okrajové podmienky pre rýchlosť a teplotu. Následne bola predstavená úprava viskozity a tepelnej vodivosti v závislosti na tlaku plynu. Tieto zmeny boli schopné popísať vplyv zníženej frekvencie zrážok častíc plynu. Predstavený model bol využitý na analýzu prúdenia cez samostatnú clonku a diferenciálne čerpanú komoru. Ďalej bol predstavený model a potrebné úpravy pre popis relativisticky pohybujúcich sa častíc. Tento model bol využitý na simulácie elektrónovej optiky. Samostatná pozornosť bola venovaná interakcii nabitých častíc s plynným prostredím. Tieto interakcie mali stochastický charakter a predstavený model popisoval ako elastické tak aj neelastické kolízie. Predstavený multi-fyzikálny model umožňuje súčasné sledovanie rôznych fyzikálnych oblastí a interakcií medzi nimi, čo vedie k možnosti detailnejšieho popisu procesov a ku zlepšeniu návrhu environmentálnych elektrónových mikroskopov.This dissertation thesis deals with the description and development of an electromagneto-hydrodynamic model intended for electron microscopy. The basis of the work lies in the description of characteristic phenomena taking place in electron microscopes with a focus on environmental electron microscopy. The work dealt with a description of the electromagnetic field, supersonic flow of rarefied gas and a motion of relativistic charged particles in a gaseous environment. An electromagnetic model based on the definition of electric and magnetic vector potential was presented and was used for a simulation of an electromagnetic coil. The supersonic flow of a rarefied gas was defined by Navier-Stokes equations. In order to extend their application to low pressures, the boundary conditions for velocity and temperature were modified. Viscosity and thermal conductivity were subsequently introduced as functions of gas pressure. These adjustments were able to describe the effects of lower collision frequency of gas particles. The presented model was used for the analysis of a flow through a separate aperture and a differentially pumped chamber. Furthermore, the model and necessary adjustments for the description of relativistically moving particles were presented. The model was used for the simulation of electron optics. Separate attention was paid to the interaction of charged particles with a gaseous environment. These interactions had a stochastic character and the presented model described both elastic and inelastic collisions. The presented multiphysics model enables the simultaneous simulation of different physical areas and the interactions between them, which leads to a possibility of a more detailed description of processes and to the improvement of environmental electron microscope design.

Implementation of density-based solver for all speeds in the framework of OpenFOAM

This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018) Abstract In the framework of open source CFD code OpenFOAM, a density-based solver for all speeds flow field is developed. In this solver the preconditioned all speeds AUSM+(P) scheme is adopted and the dual time scheme is implemented to complete the unsteady process. Parallel computation could be implemented to accelerate the solving process. Different interface reconstruction algorithms are implemented, and their accuracy with respect to convection is compared. Three benchmark tests of lid-driven ca... Title of program: allSpeedUnsteadFoam/ allSpeedUnsteadFoam_dualtime Catalogue Id: AETK_v1_0 Nature of problem This software provides a library of models for the simulation of steady and unsteady all speeds flow field (all Mach number flow field including incompressible and compressible flow). Combining this library with other libraries within OpenFOAM, such as turbulence, radiation, solid conduction, etc., the more complex multi-physics model including all speeds flow field could be established conveniently. Versions of this program held in the CPC repository in Mendeley Data AETK_v1_0; allSpeedUnsteadFoam/ allSpeedUnsteadFoam_dualtime; 10.1016/j.cpc.2014.06.00