Karpov D., Liu Z., Rolo T.D.S., Harder R., Balachandran P.V., Xue D., Lookman T., Fohtung E.
in Nature Communications, 8 (2017), 280. DOI:10.1038/s41467-017-00318-9
© 2017 The Author(s). Topological defects of spontaneous polarization are extensively studied as templates for unique physical phenomena and in the design of reconfigurable electronic devices. Experimental investigations of the complex topologies of polarization have been limited to surface phenomena, which has restricted the probing of the dynamic volumetric domain morphology in operando. Here, we utilize Bragg coherent diffractive imaging of a single BaTiO3 nanoparticle in a composite polymer/ferroelectric capacitor to study the behavior of a three-dimensional vortex formed due to competing interactions involving ferroelectric domains. Our investigation of the structural phase transitions under the influence of an external electric field shows a mobile vortex core exhibiting a reversible hysteretic transformation path. We also study the toroidal moment of the vortex under the action of the field. Our results open avenues for the study of the structure and evolution of polar vortices and other topological structures in operando in functional materials under cross field configurations.
PhD thesis, Faculty of Electrical Engineering and Information Technology, Karlsruhe Institute of Technology, 2017.
In modern particle accelerators, a precise control of the particle beam is essential for the correct operation of the facility. The experimental observation of the beam behavior relies on dedicated techniques, which are often described by the term “beam diagnostics”. Cutting-edge beam diagnostics systems, in particular several experimental setups currently installed at KIT’s synchrotron light source ANKA, employ line scan detectors to characterize and monitor the beam parameters precisely. Up to now, the experimental resolution of these setups has been limited by the line rate of existing detectors, which is limited to a few hundreds of kHz.
This thesis addresses this limitation with the development a novel line scan detector system named KALYPSO – KArlsruhe Linear arraY detector for MHz rePetition-rate SpectrOscopy. The goal is to provide scientists at ANKA with a complete detector system which will enable real-time measurements at MHz repetition rates. The design of both front-end and back-end electronics suitable for beam diagnostic experiments is a challenging task, because the detector must achieve low-noise performance at high repetition rates and with a large number of channels. Moreover, the detector system must sustain continuous data taking and introduce low-latency. To meet these stringent requirements, several novel components have been developed by the author of this thesis, such as a novel readout ASIC and a high-performance DAQ system.
The front-end ASIC has been designed to readout different types of microstrip sensors for the detection of visible and near-infrared light. The ASIC is composed of 128 analog channels which are operated in parallel, plus additional mixed-signal stages which interface external devices. Each channel consists of a Charge Sensitive Amplifier (CSA), a Correlated Double Sampling (CDS) stage and a channel buffer. Moreover, a high-speed output driver has been implemented to interface directly an off-chip ADC. The first version of the ASIC with a reduced number of channels has been produced in a 110 nm CMOS technology. The chip is fully functional and achieves a line rate of 12 MHz with an equivalent noise charge of 417 electrons when connected to a detector capacitance of 1.3 pF.
Moreover, a dedicated DAQ system has been developed to connect directly FPGA readout cards and GPU computing nodes. The data transfer is handled by a novel DMA engine implemented on FPGA. The performance of the DMA engine compares favorably with the current state-of-the-art, achieving a throughput of more than 7 GB/s and latencies as low as 2 us. The high-throughput and low-latency performance of the DAQ system enables real-time data processing on GPUs, as it has been demonstrated with extensive measurements. The DAQ system is currently integrated with KALYPSO and with other detector systems developed at the Institute for Data Processing and Electronics (IPE).
In parallel with the development of the ASIC, a first version of the KALYPSO detector system has been produced. This version is based on a Si or InGaAs microstrip sensor with 256 channels and on the GOTTHARD chip. A line rate of 2.7 MHz has been achieved, and experimental measurements have established KALYPSO as a powerful line scan detector operating at high line rates. The final version of the KALYPSO detector system, which will achieve a line rate of 10 MHz, is anticipated for early 2018.
Finally, KALYPSO has been installed at two different experimental setups at ANKA during several commissioning campaigns. The KALYPSO detector system allowed scientists to observe the beam behavior with unprecedented experimental resolution. First exciting and widely recognized scientific results were obtained at ANKA and at the European XFEL, demonstrating the benefits brought by the KALYPSO detector system in modern beam diagnostics.
First assessor: Prof. Dr. M. Weber
Second assessor: Prof. Dr.-Ing. Dr. h.c. J. Becker
Gentsos C., Fedi G., Magazzu G., Magalotti D., Modak A., Storchi L., Palla F., Bilei G.M., Biesuz N., Chowdhury S.R., Crescioli F., Checcucci B., Tcherniakhovski D., Galbit G.C., Baulieu G., Balzer M.N., Sander O., Viret S., Servoli L., Nikolaidis S.
in 2017 6th International Conference on Modern Circuits and Systems Technologies, MOCAST 2017 (2017), 7937676. DOI:10.1109/MOCAST.2017.7937676
© 2017 IEEE. The increase of the luminosity in the High Luminosity upgrade of the CERN Large Hadron Collider (HL-LHC) will require the use of Tracker information in the evaluation of the Level-1 trigger in order to keep the trigger rate acceptable (i.e.: <1MHz). In order to extract the track information within the latency constraints (<5μs), a custom real-time system is necessary. We developed a prototype of the main building block of this system, the Pattern Recognition Mezzanine (PRM) that combines custom Associative Memory ASICs with modern FPGA devices. The architecture, functionality and test results of the PRM are described in the present work.
Onelli O.D., Kamp T.V.D., Skepper J.N., Powell J., Rolo T.D.S., Baumbach T., Vignolini S.
in Scientific Reports, 7 (2017), 1373. DOI:10.1038/s41598-017-01496-8
© 2017 The Author(s). Structural colours in living organisms have been observed and analysed in a large number of species, however the study of how the micro- A nd nano-scopic natural structures responsible of such colourations develop has been largely ignored. Understanding the interplay between chemical composition, structural morphology on multiple length scales, and mechanical constraints requires a range of investigation tools able to capture the different aspects of natural hierarchical architectures. Here, we report a developmental study of the most widespread strategy for structural colouration in nature: The cuticular multilayer. In particular, we focus on the exoskeletal growth of the dock leaf beetle Gastrophysa viridula, capturing all aspects of its formation: The macroscopic growth is tracked via synchrotron microtomography, while the submicron features are revealed by electron microscopy and light spectroscopy combined with numerical modelling. In particular, we observe that the two main factors driving the formation of the colour-producing multilayers are the polymerization of melanin during the ecdysis and the change in the layer spacing during the sclerotisation of the cuticle. Our understanding of the exoskeleton formation provides a unique insight into the different processes involved during metamorphosis.
Mohr H., Dritschler T., Ardila L.E., Balzer M., Caselle M., Chilingaryan S., Kopmann A., Rota L., Schuh T., Vogelgesang M., Weber M.
in Journal of Instrumentation, 12 (2017), C04019. DOI:10.1088/1748-0221/12/04/C04019
© 2017 IOP Publishing Ltd and Sissa Medialab srl. In this work, we investigate the use of GPUs as a way of realizing a low-latency, high-throughput track trigger, using CMS as a showcase example. The CMS detector at the Large Hadron Collider (LHC) will undergo a major upgrade after the long shutdown from 2024 to 2026 when it will enter the high luminosity era. During this upgrade, the silicon tracker will have to be completely replaced. In the High Luminosity operation mode, luminosities of 5-7 × 1034 cm-2s-1 and pileups averaging at 140 events, with a maximum of up to 200 events, will be reached. These changes will require a major update of the triggering system. The demonstrated systems rely on dedicated hardware such as associative memory ASICs and FPGAs. We investigate the use of GPUs as an alternative way of realizing the requirements of the L1 track trigger. To this end we implemeted a Hough transformation track finding step on GPUs and established a low-latency RDMA connection using the PCIe bus. To showcase the benefits of floating point operations, made possible by the use of GPUs, we present a modified algorithm. It uses hexagonal bins for the parameter space and leads to a more truthful representation of the possible track parameters of the individual hits in Hough space. This leads to fewer duplicate candidates and reduces fake track candidates compared to the regular approach. With data-transfer latencies of 2 μs and processing times for the Hough transformation as low as 3.6 μs, we can show that latencies are not as critical as expected. However, computing throughput proves to be challenging due to hardware limitations.
Kaever P., Balzer M., Kopmann A., Zimmer M., Rongen H.
in Journal of Instrumentation, 12 (2017), C04004. DOI:10.1088/1748-0221/12/04/C04004
© 2017 IOP Publishing Ltd and Sissa Medialab srl. Various centres of the German Helmholtz Association (HGF) started in 2012 to develop a modular data acquisition (DAQ) platform, covering the entire range from detector readout to data transfer into parallel computing environments. This platform integrates generic hardware components like the multi-purpose HGF-Advanced Mezzanine Card or a smart scientific camera framework, adding user value with Linux drivers and board support packages. Technically the scope comprises the DAQ-chain from FPGA-modules to computing servers, notably frontend-electronics-interfaces, microcontrollers and GPUs with their software plus high-performance data transmission links. The core idea is a generic and component-based approach, enabling the implementation of specific experiment requirements with low effort. This so called DTS-platform will support standards like MTCA.4 in hard- and software to ensure compatibility with commercial components. Its capability to deploy on other crate standards or FPGA-boards with PCI express or Ethernet interfaces remains an essential feature. Competences of the participating centres are coordinated in order to provide a solid technological basis for both research topics in the Helmholtz Programme “Matter and Technology”: “Detector Technology and Systems” and “Accelerator Research and Development”. The DTS-platform aims at reducing costs and development time and will ensure access to latest technologies for the collaboration. Due to its flexible approach, it has the potential to be applied in other scientific programs.
Caselle M., Perez L.E.A., Balzer M., Dritschler T., Kopmann A., Mohr H., Rota L., Vogelgesang M., Weber M.
in Journal of Instrumentation, 12 (2017), C03015. DOI:10.1088/1748-0221/12/03/C03015
© 2017 IOP Publishing Ltd and Sissa Medialab srl. Modern data acquisition and trigger systems require a throughput of several GB/s and latencies of the order of microseconds. To satisfy such requirements, a heterogeneous readout system based on FPGA readout cards and GPU-based computing nodes coupled by InfiniBand has been developed. The incoming data from the back-end electronics is delivered directly into the internal memory of GPUs through a dedicated peer-to-peer PCIe communication. High performance DMA engines have been developed for direct communication between FPGAs and GPUs using “DirectGMA (AMD)” and “GPUDirect (NVIDIA)” technologies. The proposed infrastructure is a candidate for future generations of event building clusters, high-level trigger filter farms and low-level trigger system. In this paper the heterogeneous FPGA-GPU architecture will be presented and its performance be discussed.
Reich S., Schonfeld P., Wagener P., Letzel A., Ibrahimkutty S., Gokce B., Barcikowski S., Menzel A., dos Santos Rolo T., Plech A.
in Journal of Colloid and Interface Science, 489 (2017) 106-113. DOI:10.1016/j.jcis.2016.08.030
© 2016 Elsevier Inc. Pulsed laser ablation in liquids (PLAL) is a multiscale process, involving multiple mutually interacting phenomena. In order to synthesize nanoparticles with well-defined properties it is important to understand the dynamics of the underlying structure evolution. We use visible-light stroboscopic imaging and X-ray radiography to investigate the dynamics occurring during PLAL of silver and gold on a macroscopic scale, whilst X-ray small angle scattering is utilized to deepen the understanding on particle genesis. By comparing our results with earlier reports we can elucidate the role of the cavitation bubble. We find that symmetry breaking at the liquid-solid interface is a critical factor for bubble motion and that the bubble motion acts on the particle distribution as confinement and retraction force to create secondary agglomerates.
Wulff N.C., Van De Kamp T., Dos Santos Rolo T., Baumbach T., Lehmann G.U.C.
in Scientific Reports, 7 (2017), 42345. DOI:10.1038/srep42345
© The Author(s) 2017. Male genital organs are among the fastest evolving morphological structures. However, large parts of the male’s genitalia are often hidden inside the female during mating. In several bushcricket species, males bear a pair of sclerotized genital appendices called titillators. By employing synchrotron-based in vivo X-ray cineradiography on mating couples, we were able to visualize titillator movement and spermatophore attachment inside the female. Titillators are inserted and retracted rhythmically. During insertion the titillator processes tap the soft and sensillae-covered dorsal side of the female’s flap-like genital fold, which covers the opening of the female’s genitalia, without tissue penetration. Titillators thus appear to be initially used for stimulation; later they may apply pressure that forces the female’s genital fold to stay open, thereby aiding mechanically in spermatophore transfer.
Cecilia A., Baecker A., Hamann E., Rack A., van de Kamp T., Gruhl F.J., Hofmann R., Moosmann J., Hahn S., Kashef J., Bauer S., Farago T., Helfen L., Baumbach T.
in Materials Science and Engineering C, 71 (2017) 465-472. DOI:10.1016/j.msec.2016.10.038
© 2016 Prostate cancer (PCa) currently is the second most diagnosed cancer in men and the second most cause of cancer death after lung cancer in Western societies. This sets the necessity of modelling prostatic disorders to optimize a therapy against them. The conventional approach to investigating prostatic diseases is based on two-dimensional (2D) cell culturing. This method, however, does not provide a three-dimensional (3D) environment, therefore impeding a satisfying simulation of the prostate gland in which the PCa cells proliferate. Cryogel scaffolds represent a valid alternative to 2D culturing systems for studying the normal and pathological behavior of the prostate cells thanks to their 3D pore architecture that reflects more closely the physiological environment in which PCa cells develop. In this work the 3D morphology of three potential scaffolds for PCa cell culturing was investigated by means of synchrotron X-ray computed micro tomography (SXCμT) fitting the according requirements of high spatial resolution, 3D imaging capability and low dose requirements very well. In combination with mechanical tests, the results allowed identifying an optimal cryogel architecture, meeting the needs for a well-suited scaffold to be used for 3D PCa cell culture applications. The selected cryogel was then used for culturing prostatic lymph node metastasis (LNCaP) cells and subsequently, the presence of multi-cellular tumor spheroids inside the matrix was demonstrated again by using SXCμT.