Intense Positron Sources driven by a Superconducting Electron LINAC

The Helmholtz-Center Dresden-Rossendorf operates several user beamlines for materials research using positron annihilation energy and lifetime spectroscopy. The superconducting electron LINAC ELBE [1] drives a hard X-ray source which is used to generate positrons through pair production. The unique setup Gamma-induced Positron Source GiPS generates electron-positron pairs inside the sample under investigation directly [2] making it well suited for annihilation lifetime studies of materials which are not qualified for vacuum conditions or because they impose hazards or intrinsic radioactivity.
The high-intensity Mono-energetic Positron Source MePS utilizes moderated positrons with adjustable kinetic energies ranging from 500 eV to 18 keV [3] for depth profiling in thin films. A magnetic beam transport system consisting of a beam chopper, a beam buncher, and a post-accelerator guides the positron beam towards the sample under investigation. Full-digital data processing of positron annihilation lifetime events generates spectra nearly free from background and free from distortions with timing resolutions down to about 210 ps and count rates in excess of 120 kcps.
The MePS facility is currently complemented by an additional beamline named Apparatus for In-situ Defect Analysis, AIDA-II, where in-situ defect studies are to be performed in a wide temperature range during thin film growth and under ion irradiation. A complimentary but functionally similar setup, AIDA-I [4], is operated at a 22Na-based mono-energetic continuous positron beam [5] used for in-situ (coincidence) Doppler-broadening positron annihilation spectroscopy experiments.
All facilities serve as user facilities to the international scientific community. Recent developments at all beam lines and some exemplary experiments will be presented [6-8].

The MePS facility has partly been funded by the Federal Ministry of Education and Research (BMBF) with the grant PosiAnalyse (05K2013). The initial AIDA system was funded by the Impulse- und Networking fund of the Helmholtz-Association (FKZ VH-VI-442 Memriox). The AIDA facility was funded through the Helmholtz Energy Materials Characterization Platform.

References
[1] F. Gabriel, et al., Nucl. Instr. Meth. B 161 (2000) 1143.
[2] M. Butterling, et al., Nucl. Instr. Meth. B 269 (2011) 2623.
[3] A. Wagner, et al., AIP Conference Proceedings 1970 (2018) 040003.
[4] M. O. Liedke, et al., Journal of Applied Physics 117 (2015) 163908.
[5] W. Anwand, et al., Defect and Diffusion Forum Vl. 331 (2012) 25.
[6] M. Reiner, et al., Scientific Reports 6 (2016) 29109.
[7] A. Quintana, et al., ACS Nano 12 (2018) 10291.
[8] J. Ji, et al., Scientific Reports 6 (2016) 31238.