Report/Dissertation / PhD Thesis

PUBDB-2015-05411

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Development and characterization of electron sources for diffraction applications

Casandruc, A. (Corresponding author)>Extern*

2015
Verlag Deutsches Elektronen-Synchrotron Hamburg

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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2015-051

Report No.: DESY-THESIS-2015-051

Abstract: The dream to control chemical reactions that are essential to life is now closer than ever to gratify. Recent scientific progress has made it possible to investigate phenomena and processes which deploy at the angstroms scale and at rates on the order femtoseconds. Techniques such as Ultrafast Electron Diffraction (UED) are currently able to reveal the spatial atomic configuration of systems with unit cell sizes on the order of a few nanometers with about 100 femtosecond temporal resolution. Still, major advances are needed for structural interrogation of biological systems like protein crystals, which have unit cell sizes of 10 nanometers or larger, and sample sizes of less than one micrometer. For such samples, the performance of these electron-based techniques is now limited by the quality, in particular the brightness, of the electron source. The current Ph.D. work represents a contribution towards the development and the characterization of electron sources which are essential to static and time-resolved electron diffraction techniques. The focus was on electron source fabrication and electron beam characterization measurements, using the solenoid and the aperture scan techniques, but also on the development and maintenance of the relevant experimental setups. As a result, new experimental facilities are now available in the group and, at the same time, novel concepts for generating electron beams for electron diffraction applications have been developed. In terms of existing electron sources, the capability to trigger and detect field emission from single double-gated field emitter Mo tips was successfully proven. These sharp emitter tips promise high brightness electron beams, but for investigating individual such structures, new engineering was needed. Secondly, the influence of thesurface electric field on electron beam properties has been systematically performed for flat Mo photocathodes. This study is very valuable especially for state-of-the-art electron guns where acceleration electric fields as high as 100 MV/m are possible. Regarding the developmentof novel electron sources, the fabrication of patterned photocathode structures, consisting of micrometric emitters was analyzed. These could bring major advantages in terms of electron beam quality, due to the possibility of controlling the size and the shape of the emitting area. On the other hand, first beam characterization measurements of a new type of electron source, based on optical fibers, were performed. While these structures hold all the advantages of the patterned electron sources discussed above, they proved to be much easier to fabricate and their use require no alignment of optical elements inside vacuum, which is usually subject of setup constraints.The experimental output of the current Ph.D. work is very promising and pave the way to a new generation of diffraction experiments with capabilities exceeding the limitations faced before.

Note: Universität Hamburg, Diss., 2015

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Contributing Institute(s):

1. Forschungsgruppe für strukturelle Dynamik (MPSD)

Research Program(s):

1. 631 - Accelerator R & D (POF3-631) (POF3-631)

Experiment(s):

1. Relativistic Electron Gun for Atomic Exploration

Appears in the scientific report 2015

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Database coverage:

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