The Small Thermalized Electron Source at Mainz (STEAM) is a dc photoemission source. It is designed to operate at up to 200 kV bias voltage with an accelerating field of up to 5MV m−1 at the cathode ...surface. In several experiments, the properties of GaAs operating under the conditions of spin-polarized photoemission were investigated. Its performance, quantum efficiency lifetime and surface charge limit observations for bulk-GaAs will be discussed.
Low-energy beam transport system for MESA Matejcek, C.; Aulenbacher, K.; Friederich, S.
Journal of physics. Conference series,
11/2019, Letnik:
1350, Številka:
1
Journal Article
Recenzirano
Odprti dostop
An important part of the new accelerator MESA (Mainz Energy-recovering Superconducting Accelerator) is the low-energy beam transport system connecting the 100 keV electron source with the injector. ...The present setup includes the chopper and bunching system. The devices are of highest importance in order to achieve sufficient bunch compression, particularly at higher bunch charges and currents. With the circularly deflecting cavity of the chopper system it is possible to measure the longitudinal profile of the bunches upstream of the buncher, whereas downstream the longitudinal size will be measured by Smith-Purcell radiation. Based on experimental results obtained from this setup, we will discuss the beam parameters and compare them with simulations of the beamline.
At least 15 settlement layers, deposited above each other from the early Neolithic (ca. 5300 cal BC) until Roman Imperial Times (ca. 400 cal AD), have been discovered at Niederröblingen, Germany. ...Constituting the longest duration of prehistoric settlement in central Europe so far known (ca. 4000 yrs), the site is thought to represent the first multi-layered settlement mound (tell?) north of the Alps. This implicates that the occurrence of settlement mound is not limited to the circum-Mediterranean area. The detailed chronology, based on archaeological, radiocarbon and OSL dating and supporting a Bayesian model, shows one clear occupational gap (early Neolithic) and a possible hiatus (Roman Times). Erosion phases of the settlement mound and the deposition of alluvial sediments (since Roman Imperial Times) in the surroundings resulted in an almost complete disappearance of the mound from the recent scenery. Being difficult to detect, similar sites might be present, undetected, in central Europe. Their discovery and study would enable the precise reconstruction of the settlement history as well as of the prehistoric man–environmental interactions at a high resolution.
► We discovered the first multilayered settlement mounds north of the Alps. ► Multilayered settlement hills are not restricted to the circum-Mediterranean region. ► The settlement mound at Niederröblingen comprises of at least 15 settlement layers. ► Settlement activity spanning from 5300 BC until 400 AD, interrupted for 2000 years. ► 2 OSL and 30
14C dates were modelled with Oxcal 4.1. (Bayesian).
A test set-up for electron collector efficiency measurements Bruker, M.W.; Friederich, S.; Aulenbacher, K.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2017, Letnik:
872
Journal Article
Recenzirano
A low-energy test set-up for the measurement and optimisation of secondary electron currents from the collector in electron coolers is presented. A variable-field Wien filter and current-measuring ...aperture plates grant insight into the trajectory and energy distribution of the secondary particles. While secondary electrons flowing back from the collector can be bent away and dumped, these electrons in turn create new secondaries (“tertiaries”), and the resulting cascade is what ultimately limits the performance of the whole collector assembly, i.e. collector, optics, and Wien filter as a complete unit. Our set-up aims at understanding the behaviour of secondary and tertiary electrons inside this assembly. Using the included diagnostic devices, the efficiency of the collector itself can be measured as a function of the beam parameters and optics; some measurements of a COSY-style collector are given as an example.
The later Wittgenstein's perspective on mathematical sentences as norms is motivated for sentences belonging to Hilbertian axiomatic systems where the axioms are treated as implicit definitions. It ...is shown that in this approach the axioms are employed as norms in that they function as standards of what counts as using the concepts involved. This normative dimension of their mode of use, it is argued, is inherited by the theorems derived from them. Having been motivated along these lines, Wittgenstein's perspective on mathematical language may appeal also to those who are not friends of or experts on Wittgenstein's later philosophy of mathematics. PUBLICATION ABSTRACT
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