Search

Langmuir probes are used on our faculty to measure current-voltage characteristics of low-temperature weakly ionized plasma. From these measurements an electron temperature and an electron number density are obtained. Classical method of doing that is based on the linear least squares fitting. In this thesis we use neural networks as an alternative method of determining the plasma parameters. We train a feedforward neural network with a help of a stochastic gradient descent and a backpropagation algorithms together with a training data based on an analytical model the characteristic. We study network's accuracy, robustness and computational resources demands, all compared with the classical methods. Powered by TCPDF (www.tcpdf.org)

In investigating the behaviour of the plasma, it is important to know its parameters. For this purpose, there are many diagnostic methods, one of which is a probe diagnostic. It is a local method in which there is contact of the plasma with embedded material. This work deals with this diagnostic method. It gives a comprehensive overview of the currently used probes in low-temperature and especially in high-temperature plasmas. It focuses on the development and use of the latest advances in the field of computational physics for creating two-dimensional model of low-temperature plasma with immersed solid. The task is prepare particle model of low-temperature plasma with immersed metal electrode, then run simulation of measurement and to interpret measured data.

During my master thesis I became familiar with ion imaging and velocity map imaging (VMI) techniques in experiments with molecular beam. My major contribution was writing a computer program for data acquisition and pre-analysis. The program features initial filtering of the data, improving significantly signal to noise ratio. Non-trivial effort was required to make the program compatible with three different CCD cameras implemented on different experiments in the laboratory. I have also simulated ion trajectories in VMI and wrote a program code to imulate VMI image distortions due to imperfections in apparatus geometry. These programs will be useful in aligning and tuning the apparatus. Finally, I wrote a program for data manipulation and conversion to formats compatible with various data analysis programs available in the laboratory. All the above programs I have tested by measurements of 243 nm photodissociation of HBr molecules.

1 Abstract: For understanding of the evolution of chemical composition in cold interstellar gas clouds, it is necessary to study the ion-molecule reactions at temperatures from 10 K to 300 K at low pressures. The Ion Trap equipment, which is available in the laboratory of the Department of Surface and Plasma Science, allows this type of experiment. The main element of the Ion Trap is a 22-pole radiofrequency trap that examined reactions take place. For capturing ions in the trap, they need to be well focused in space, time and energy. To meet these conditions, it is necessary to find a suitable parameters of the source, which is used in the laboratory. The aim of this bachelor thesis is the design of optimized ion source and then using the program in LabVIEW to optimize the ion source N+ .