Speaker
Description
Positron annihilation lifetime spectroscopy (PALS) is a powerful tool for investigating defects in various materials. In order to study inhomogeneous defect distributions, e.g., close to fatigue cracks or dispersive alloy using PALS, a monochromatic pulsed positron beam of variable energy with a diameter in the range of 1 µm and a pulse width of 150 ps FWHM required.
To this aim, the Scanning Positron Microscope (SPM) [1-2] was developed and built at the Universität der Bundeswehr München. To overcome the limit of low count-rates the SPM has been completely transferred to the intense positron source NEPOMUC at the MLZ in Garching (FRM II).
A sophisticated beam preparation, including multiple remoderation steps, is needed to reach a lateral resolution in the micro-meter range. An essential SPM interface component is the positron elevator [3] which compensates for the energy loss caused by the remoderation processes without altering other important beam properties like time structure or brightness. To ensure proper operation of the SPM at NEPOMUC, a stable amplitude, frequency, and phase of the RF-signal are crucial [4].
This contribution will give an overview of the SPM's current status, which has undergone a complete makeover during the reactor shutdown. In addition, we will report on the latest developments of the positron elevator and the newly developed frequency stabilization system and discuss future applications of the SPM.
References
[1] W. Triftshäuser et al., NIM-B, Volume 130, Pages 264-269, (1997).
[2] G. Kögel et al., Appl. Surf. Sci., Volume 116, Pages 108-113, (1997).
[3] M. Dickmann et al., NIM-A, Volume 821, Pages 40-43, (2016).
[4] J. Mitteneder et al., AIP Conf. Proc. 2182 (1): 040002 (2019).
