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Beam Dynamics Optimization for a High-brightness Photo Injector with various Photocathode Laser Pulse Shapes
No full textPITZ at DESY Zeuthen focuses on the development and optimization of high-brightness electron sources for the European XFEL. At PITZ, a thorough study of factors influencing emittance growth is carried out. Emittance growth due to space charge can be managed through precise laser pulse shaping techniques. 4D and 6D Integral brightness that incorporates not only the emittance, but electron beam current profile and longitudinal phase space properties from laser pulse shapes are proposed as objectives for the optimization. Multiobjectve optimization studies with ASTRA are aimed at not only minimizing emittance but maximizing brightness for various laser temporal profiles and widths. A comparative analysis for Gaussian, flattop and ellipsoidal and inverted parabolic Laser profiles is presented to compare their efficiency not only in terms of emittance but 4D and 6D brightness
A proposal for the Lohengrin experiment to search for dark sector particles at the ELSA Accelerator
No full textWe present a proposal for a future light dark matter search experiment at the Electron Stretcher Accelerator ELSA in Bonn: Lohengrin. It employs the fixed-target missing momentum based technique for searching for dark-sector particles. The Lohengrin experiment uses a beam of electrons that is extracted from the ELSA accelerator and that is shot onto a thin target to produce mainly Standard Model bremsstrahlung and – in rare occasions – possibly new particles coupling feebly to the electron. A well motivated candidate for such a new particle is the dark photon, a new, possibly massive gauge boson arising from a new gauge interaction in a dark sector and mixing kinetically with the Standard Model photon. The Lohengrin experiment is estimated to reach sensitivity to couplings small enough to explain the relic abundance of dark matter in various models for dark photon masses between and
ALD‐Assisted VO for Memristor Application
No full textVanadium dioxide (VO) is a well-known candidate for memristor applications due to its insulator-to-metal transition (IMT) characteristics. The fabrication of memristor devices requires highly controlled synthesis processes concerning the material chemistry and geometry. Atomic layer deposition (ALD) offers unique advantages for the fabrication of hardware neural networks, such as miniaturization, conformality, and sub-nm thickness control. Herein, an ALD process for non-stoichiometric vanadium oxide (VO) using tetrakis(dimethylamino)vanadium (TDMAV) and water as precursors is presented. Subsequently, a tailor-made annealing process converts VO into VO, which exhibits an IMT of about three orders of magnitude at around 70 °C, rendering it a promising memristor material. VO thin film and Si–AlO/VO core/shell memristors are fabricated and analyzed, both of which exhibited I–V hysteresis loops, indicating their suitability for memristor applications in both 2D and 3D morphologies. Additionally, these memristors are sensitive to the operation temperature, with the hysteresis loops narrowing and shifting toward lower voltages as temperature increases, eventually disappearing beyond VO's intrinsic phase transition temperature. This study highlights the viability of ALD-assisted VO for memristor applications and demonstrates its potential for advancing the three-dimensionalization of neuromorphic chips
Balancing strength and ductility in MP159 superalloy (Co–Ni–Cr–Fe–Mo–Ti–Al–Nb) through severe plastic deformation and multistage heat treatments
No full textThis study investigated the enhancement of room-temperature mechanical properties in the Co-Ni-Cr-Fe-Mo-Ti-Nb-Al MP159 superalloy through severe plastic deformation via high-ratio differential speed rolling (HRDSR), followed by controlled annealing and aging treatments. Partial recrystallization during annealing produced a microstructure comprising recrystallized and unrecrystallized grains, enabling a favorable balance between strength and ductility. Optimal annealing at 1123 K for 48 h produced a partially recrystallized microstructure, consisting of fine recrystallized grains (∼2.2 μm) embedded in unrecrystallized regions. This microstructural configuration yielded a high yield strength of 0.83 GPa and a uniform elongation of 18.3 %. Subsequent aging promoted the formation of nanoscale L12-type γ′ precipitates, further increasing the yield strength to 1.1 GPa while maintaining good uniform ductility (∼12 %). The mechanical response was analyzed considering grain refinement, dislocation density, recrystallization behavior, and precipitation strengthening. This integrated thermo-mechanical approach provides a practical and effective means of enhancing the strength–ductility synergy in MP159 superalloys for advanced structural applications
Tracking in Dense Environments with Transformers
No full textThis work presents a novel application of machine learning to the pattern-recognition stage of charged-particle reconstruction, enabling learned hit-to-track association within dense environments, such as the cores of high-pTjets. Our Transformer-based architecture is based on a MaskFormer model that jointly optimises hit assignments and the estimation of the charged particles' properties. Trained and evaluated in dense environments the model delivers up to a 30% improvement in track-reconstruction efficiency over the standard ATLAS reconstruction when local particle density makes conventional reconstruction most challenging.Scientific contact person Juste Rozas, Aurelio, ([email protected]
Experimental study and modeling of the microstructural effects on the mechanical behavior of Ti-6Al-4V titanium alloy
No full textThis work is devoted to studying the coupled effect of grain size and crystallographic texture on the mechanicalbehavior at room temperature of Ti–6Al–4V alloy with an equiaxed microstructure. To this end, experimentaldata was collected on a broad range of mechanical solicitation conditions through monotonic and cyclic tests,followed by macroscopic elasto-viscoplastic modeling.The experimental results show that the mechanical behavior of Ti–6Al–4V is mainly influenced by boththe grain size and the crystallographic texture. The microstructure with the finest grain size exhibits thehighest flow stress. The weakly textured alloy presents the highest ductility. Moreover, all the Ti–6Al–4Vmicrostructures present cyclic softening behavior. In addition, at room temperature, no microstructure wasfound to exhibit significant strain rate sensitivity. The results also show that the grain size affects the yieldstrength of the Ti–6Al–4V alloy, as well as its ductility and its kinematic hardening.The proposed model formulation accurately predicts the effect of the microstructural features of theTi–6Al–4V alloy. Isotropic and kinematic hardening laws are modified by introducing the grain size effectsvia the Hall-Petch relationship
A search for dark matter produced in association with a dark Higgs boson decaying into a Higgs boson pair in 3 or 4 final states using collisions at TeV with the ATLAS detector
No full textA search is performed for dark matter particles produced in association with a resonant pair of Higgs bosons using 140 fb of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. This signature is expected in some extensions of the Standard Model predicting the production of dark matter particles, and is interpreted in terms of a dark Higgs model containing a Z′ mediator in which the dark Higgs boson s decays into a pair of Higgs bosons. The dark Higgs boson is reconstructed through final states with at least three b-tagged jets, produced by the pair of Higgs boson decays, in events with significant missing transverse momentum consistent with the presence of dark matter. The observed data are found to be in good agreement with Standard Model predictions, constraining scenarios with dark Higgs boson masses within the range of 250 to 400 GeV and Z′ mediators up to 2.3 TeV.[graphic not available: see fulltext
Impact of hot and warm deformation on the bainite morphology and kinetics during continuous cooling of low- and medium-C carbide-free bainitic steels
No full textThis work aims to describe the microstructural evolution of bainite during continuous cooling from austenite with varying grain size, morphology and defect density in two carbide-free bainitic steels with low and medium C contents. To achieve these conditions, hot and warm deformations were applied, and compared to an undeformed condition. Thermomechanical treatments were performed with a dilatometer and monitored in-situ via high-energy X-Ray diffraction. EBSD was employed for identifying the variant pairing behaviour and misorientation distributions. In comparison to the undeformed condition, a delay in the transformation kinetics was observed for the deformed conditions of both steels. The delay was correlated to the dislocation density of austenite before the onset of the bainitic transformation. Due to the delay, the bainite transformation temperature was lower in the deformed conditions. In spite of this, there was an increase in the frequency of low-angle misorientation boundaries as given by the misorientation distributions. This effect is unexpected in view of established thermodynamic models for prediction of the bainite morphology. This discrepancy was attributed to the substructure introduced by the deformation, which was inherited by bainite. A microstructure evolution history was proposed based on the concurring metallurgical phenomena during the deformation and subsequent continuous cooling
Novel silicon and GaAs sensors for compact sampling calorimeters
No full textTwo samples of silicon pad sensors and two samples of GaAs sensors are studied in an electron beam with 5 GeV energy from the DESY-II test-beam facility. The sizes of the silicon and GaAs sensors are about 9 9 and 5 8 , respectively. The thickness is 500 µm for both the silicon and GaAs sensors. The pad size is about 5 5 . The sensors are foreseen to be used in a compact electromagnetic sampling calorimeter. The readout of the pads is done via traces connected to the pads and the front-end ASICs at the edges of the sensors. For the silicon sensors, copper traces on a Kapton foil are connected to the sensor pads with conducting glue. The pads of the GaAs sensors are connected to bond-pads via aluminium traces on the sensor substrate. The readout is based on a dedicated front-end ASIC, called FLAME. Pre-processing of the raw data and deconvolution is performed with FPGAs. The whole system is orchestrated by a Trigger Logic Unit. Results are shown for the signal-to-noise ratio, the homogeneity of the response, edge effects on pads, cross talk and wrongly assigned signals due to the readout traces
Multimodal structural humidity-response of cellulose nanofibril foams derived from wood and upcycled cotton textiles
No full textWe have produced foams from cellulose nanofibrils from upcycled cotton (upCNF) and wood (wCNF) through unidirectional (UIT) and multidirectional ice-templating (MIT) and investigated the structural humidity response through in-situ WAXS, SAXS, and micro tomography (μCT) between 10 and 95 % relative humidity (RH). The upCNF and wCNF WAXS patterns displayed a shape- and position shift as the RH was increased, with a compression in the (200) direction and an elongation in the (004) direction. The average separation distance extracted from the 1D SAXS patterns revealed no significant change for the upCNF foams regardless of RH and processing route, while a significant increase was observed for the wCNF foams. The μCT measurements of the upCNF foams showed a slight shift in macropore distribution towards larger pores between 50 and 80 % RH which can be attributed to the weakening and partial disintegration of the pore wall as more moisture is introduced. The humidity-induced structural alterations of the upCNF foam were significantly lower compared to the wCNF foams, confirming our claim of upCNF being more moisture resistant than wCNF foams