Berlin 2008 – wissenschaftliches Programm

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VA: Fachverband Vakuumphysik und Vakuumtechnik

VA 4: NEPOMUC positron source and experiments

VA 4.3: Vortrag

Montag, 25. Februar 2008, 16:00–16:20, H 0106

A new device for a pulsed positron beam at the NEPOMUC positron facility — •Christian Piochacz^1,2, Gottfried Kögel², Werner Egger², Christoph Hugenschmidt¹, Peter Sperr², and Günther Dollinger² — ¹ZWE FRM II, TU München, Lichtenbergstraße 1, 85747 Garching — ²LRT 2, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, 85577 Neubiberg

Positron annihilation is a highly sensitive method to study defects of atomic size. Both, the types and the concentrations of defects can be determined by positron lifetime measurements. To perform such measurements with micrometer spatial resolution, a pulsed positron beam is focused down to micrometer spot size in the Munich Scanning Positron Microscope (SPM). For a much higher event rate it is intended to operate this SPM at the high intense positron source NEPOMUC at the FRM II. Since April 2007 a remoderated positron beam of sufficient brilliance is available at NEPOMUC.

The new pulsing device must transform this dc-beam into a train of sharp pulses without losing much intensity. Therefore, a two stage pulsing concept is applied, where a pre-buncher concentrates the intensity into the nanosecond time windows of the resonant sine wave main buncher. The new device has been completed and installed at the open beam port of NEPOMUC. We present the design concepts and results from both, particle tracing simulations and first measurements.