On the Challenges for Time-of-Flight Electron Spectroscopy at Storage Rings
Sammanfattning: Time-of-flight (TOF) techniques for energy analysis have been common in electron spectroscopy for many decades. TOF-based electron spectrometers benefit from higher transmission and information rate compared to their main competitor: the hemispherical analyser; the drawback being their lower energy resolution. However, the advent of angle-resolved TOF spectrometers for electron energy analysis challenges this perception. State-of-the-art TOF analysers, such as the Scienta ARTOF, offer energy resolution comparable to the hemispherical analyser resolution, while keeping the high transmission. Electron TOF should therefore be valuable complementary instrumentation at any future high-brilliance storage rings such as MAX IV. TOF instruments demand pulsed light with comparably low repetition rates. At storage rings they often rely on the availability of single bunch modes with lower pulse repetition rates. However, time-sharing limits the beamtime available both for timing based instrumentation and experiments, and for those demanding high intensity. Solutions to allow simultaneous operation are therefore critical for the user community. This thesis explores four classes of solutions: Accelerator adaptations, choppers, instrument gating and coincidence techniques. A review of accelerator adaptations, choppers and coincidence techniques is presented which in particular highlights future opportunities for timing based experiments at MAX IV. With regard to gating, this thesis reports the development of an electronic gate for the ARTOF analyser. It is showed how a pulsed electric potential and a system of transmission meshes can be used to simulate single bunch operation and discard electrons which would be unresolvable in the analyser. One paper shows how a detector gate has been implemented to allow use of the instrument in hybrid mode at BESSY storage ring in Berlin. We show that detection efficiency can be increased more than ten times. A second paper discusses the necessary requirements to build a similar gate for the operation mode of the future MAX~IV rings and outlines some initial experimental results.
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