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G. Kowarik:
"Investigations on ion induced electron emission from fusion-relevant surfaces";
Betreuer/in(nen): F. Aumayr; Institut für Allgemeine Physik, 2007; Abschlussprüfung: 27.02.2007.

Aim of the present work was the development of a measurement system, capable of determining total ion-induced electron emission yields from conducting surfaces, which fits into an existing UHV recipient, and is, at the same time, capable of measuring energy distributions for the emitted electrons. A current method with collector was used to measure the currents on target and collector. A proper software had to be developed, in order to control the electronics, acquire data, and evaluate the obtained raw-data. Following a proof-of-principle-phase using gold, the goal was the measurement of electron emission parameters from fusion-relevant, technical surfaces, due to ion impact of fusion-relevant ions.
The measurements were performed under good HV conditions, using projectile ions from our ECRIS, which is capable of delivering reasonable currents of multiply charged ions.
As fusion-relevant material, tungsten was used as a target, which is a candidate for the divertor plates in a possible future fusion reactor.
Tungsten is investigated in the present work with respect to the total electron emission as well as the energy distributions of the emitted particles.
During the calibration phase of the system, time dependent yield variations were observed. A simple model is presented, in order to qualitatively explain the behaviour. The model hints ion implantation to be the driving process, which is compared to adsorption and production of defects.
Additionally, measurements with another system have been performed, which investigate the internal excitation of electrons in the bulk material, i.e. electrons with less energy than necessary to cause emission. Therefore, special tunnel junctions (MIM), built by a German group, have been transported to the ECRIS, and investigated here.