We present techniques for diagnosing magnetically confined electron-positron pair plasma [1]. Direct and positronium-mediated annihilation result in overlapping volumetric γ sources, and the 2-γ emission from these volumetric sources can be tomographically reconstructed from coincident counts in multiple detectors. Transport processes result in localized annihilation where field lines...
Positron annihilation lifetime spectroscopy (PALS) is a sensitive technique to analyze the type and concentration of lattice defects on an atomic level.
We applied ex-situ PALS to plastically deformed technical Al and Al alloys.
We measured the depth-dependent positron lifetime at the accelerator-based positron source MEPS at ELBE.
For each sample we recorded the tensile stress, and the...
The mission of the APEX-LD (A Positron-Electron eXperiment - Levitated Dipole) trap is to provide a compact (~10-liter) volume of closed dipole magnetic field lines, to be used for the confinement and study of low-temperature, long-lived e+e- pair plasmas. The requirements for this application posed a number of challenges for experiment design and engineering. (These included, e.g., the need...
In the field of continuous low energy particle beams, Faraday cup detectors have been traditionally considered a way of precisely assessing the particle flux, given a few minutes of integration time and assuming no spatial resolution is required. Two years ago we presented a novel Faraday cup design, pursuing the aim is of providing fast and position-sensitive measurements. We will present now...
Structurally complex materials provide many different possible trapping sites for positrons. Especially, positron lifetime spectra of samples with µm and sub-µm sized grains must be carefully analysed, as positron trapping and annihilation in grain boundaries plays an increasingly important role and cannot be neglected anymore, even when other defect types are in the primary focus. To properly...
$\beta^+$ emitters are essential for positron based defect spectroscopy experiments that require compact setups. In this thesis, weak $^{22}$Na positron sources have been produced by irradiating aluminum targets with a 68 MeV proton beam. This approach avoids wet chemical processes, which are used in commercial production of carrier-free $^{22}$Na positron sources. The design of the target...
The Coincidence Doppler Broadening Spectrometer (CDBS) at the NEutron induced POsitron source MUniCh (NEPOMUC) uses positrons as a microprobe to investigate material defects on an atomic level. The instrument can give insights into open volume defect concentrations in samples. However, additionally, by utilizing the coincidence feature and advanced evaluation software the chemical environment...
The Coincidence Doppler Broadening (CDB) spectrometer with its monoenergetic scanning positron beam allows the investigation of defect distributions in three dimensions (3D) and the elemental surrounding of open-volume defects. With thsi instrument we address the following scientific questions: Homogeneity of samples, i.e. depth and lateral distribution of lattice defects. Examples are (laser...
Antimony selenide (Sb$_2$Se$_3$) is photovoltaic material with an optimal bandgap and a high optical absorption coefficient comprising of earth abundant elements. Solar cell power conversion efficiencies initially increased markedly but more recently the rate of increase has slowed. There is a large open circuit voltage consistent with the presence of detrimental concentrations of point...
