Development, Characterization, and Analysis of Silicon Microstrip Detector Modules for the CBM Silicon Tracking System

The future Facility for Antiproton and Ion Research (FAIR) at GSI, Germany, will enable scientists to create tiny droplets of cosmic matter in the laboratory—matter subject to extreme conditions usually found in the interior of stars or during stellar collisions. The Compressed Baryonic Matter (CBM) experiment at FAIR aims to explore the quantum chromodynamics (QCD) phase diagram at high densities and moderate temperatures. By colliding heavy ions at relativistic beam energies, the conditions inside these supermassive objects can be recreated for an exceptionally short amount of time. The CBM detector is a fixed-target multi-purpose detector designed for measuring hadrons, electrons and muons in elementary nucleon and heavy-ion collisions over the full FAIR beam energy range delivered by the SIS100 synchrotron. One of the core detectors of CBM is the Silicon Tracking System (STS), responsible for measuring the momentum and tracks of up to 700 charged particles produced in a central nucleus-nucleus collisions. Due to the required momentum resolution, the material budget of the STS must be minimized. Therefore, the readout electronics and the cooling and mechanical infrastructure are placed out of the detector acceptance. The double-sided silicon microstrip sensors are connected to the self-triggering frontend electronics using low-mass flexible microcables with a length of up to 50 cm. The main goal of this thesis was to develop a high-density interconnection technology based on copper microcables. We developed a low-mass double-layered copper microcable at the edge of modern fabrication technology. Based on the copper microcable, we developed a novel high-density interconnection technology, comprising fine-grain solder paste printing on the microcable and gold stud bumping on the die. The gold stud--solder technology combines a high automation capability with good mechanical and electrical properties, making it an interesting technology also for future detector systems. Building on the gold stud--solder technology, a fully customized bonder machine was developed and constructed in hardware and software. Its main purpose is the realization of the challenging interconnection between the microcable and the sensor. Key components of the machine are four step motors with a sub-micron step resolution, a dual-camera pattern recognition system, a heatable, temperature-controlled bond head and sensor plate, as well as tailor-made mechanical supports for the STS detector modules. With the help of this bonder machine, a full-scale STS detector module in the copper technology was built. The noise performance of the copper module was evaluated in a bias voltage scan. Very low noise levels were observed. Measurements of the absolute value of the signal with a radioactive source allowed us to estimate the signal-to-noise ratio of the module. The results of these measurements give us confidence that STS modules based on the copper technology can achieve a satisfying performance comparable to the modules built in the aluminium technology. Another essential component of the STS detector module is the frontend electronics chip. During this work, the version 2.1 of the STS-XYTER readout ASIC was extensively characterized. Noise discrepancies between odd and even channels and increasingly higher noise towards the higher channel numbers had been observed in the predecessor chip. Our measurements of the STS-XYTER2.1 verified that both issues were successfully resolved. Furthermore, the noise behavior of the ASIC with respect to input load capacitance was studied. This is essential to parametrize expected noise levels for the many kinds of detector modules employed in the STS, to which the measured noise levels can then be compared. Measurements of the noise levels as a function of shaping time showed that the overall noise level is practically independent of shaper peaking time. Radiation tests with 50 MeV protons were performed with copper microcables connected to the ASIC in a non-powered state. No indications of damage to the chip and interconnects could be observed. Finally, a complete STS detector module in aluminium technology was subjected to a pencil-like monochromatic beam of 2.7 GeV/c protons at the Cooling Synchrotron at the research center Jülich. Several essential performance criteria of the detector module were evaluated. The best coincidence between the STS and the reference fiber hodoscopes was established based on time information. An excellent time resolution of a few nanoseconds could be demonstrated. Based on the best coincidence, the spatial resolution of the full system was determined to be a few hundred microns. This is in line with expectations, as the resolution is limited by the fiber hodoscope resolution. Charge distributions of 1-strip clusters showed a clear separation between the noise and the proton signal peak, with a signal-to-noise ratio above 20 for the p-- and n-side. The charge collection efficiency of the module was estimated to be $96 \%$. The COSY beamtime enabled a first-time evaluation of the full analysis software chain with real data and the evaluation of the full electronic readout chain of STS. The experience gained at COSY is immensely helpful for commissioning and data analysis in more complex beam environments such as mCBM, where a subsample of the CBM detectors is exposed to the particles created in a heavy-ion collision in run-time scenarios closely resembling the final CBM environment

Dice-and-fill single element octagon transducers for next generation 3D USCT

At the Karlsruhe Institue of Technology (KIT), a 3D-Ultrasound Computer Tomography (3D-USCT) medical imaging system for early breast cancer detection is currently developed. With the next generation of 3D-USCT 2.5, the current region of interest (ROI) of 10 x 10 x 10 cm³ shall be increased to 20 x 20 x 20 cm³ to allow reliable imaging results also for bigger female breasts. Therefore, the opening angle (OA) of the future transducers should be increased to approx. 60° at 3 dB while other characteristics such as bandwidth (BW) and resonance frequency should be preserved or even improved. Based on the current dice-andfill approach in transducer production, optimization is performed on piezoelectric sensor geometry and size, type and structure of matching and backing layer and interconnection technology of the several parts of the transducer

Piezofibre composite transducers for next generation 3D USCT

At the Karlsruhe Institue of Technology (KIT), a 3D-Ultrasound Computer Tomography (3D-USCT) medical imaging system for early breast cancer detection is currently developed. With the next generation of 3D-USCT 2.5, the current region of interest (ROI) of 10 x 10 x 10 cm³ shall be increased to 20 x 20 x 20 cm³ to allow reliable imaging results also for bigger female breasts. Therefore, the opening angle (OA) of the future transducers should be increased to approx. 60 ° at 3 dB while other characteristics such as bandwidth (BW) and resonance frequency should be preserved or even improved. Based on Fraunhofer IKTS Piezofibre composites utilized for transducer production, an optimization is performed on piezoelectric sensor geometry and size, type and structure of matching and backing layer and interconnection technology of the several parts of the transduce

mTORC1 Is Transiently Reactivated in Injured Nerves to Promote c-Jun Elevation and Schwann Cell Dedifferentiation

Schwann cells (SCs) are endowed with a remarkable plasticity. When peripheral nerves are injured, SCs dedifferentiate and acquire new functions to coordinate nerve repair as so-called repair SCs. Subsequently, SCs redifferentiate to remyelinate regenerated axons. Given the similarities between SC dedifferentiation/redifferentiation in injured nerves and in demyelinating neuropathies, elucidating the signals involved in SC plasticity after nerve injury has potentially wider implications. c-Jun has emerged as a key transcription factor regulating SC dedifferentiation and the acquisition of repair SC features. However, the upstream pathways that control c-Jun activity after nerve injury are largely unknown. We report that the mTORC1 pathway is transiently but robustly reactivated in dedifferentiating SCs. By inducible genetic deletion of the functionally crucial mTORC1-subunit Raptor in mouse SCs (including male and female animals), we found that mTORC1 reactivation is necessary for proper myelin clearance, SC dedifferentiation, and consequently remyelination, without major alterations in the inflammatory response. In the absence of mTORC1 signaling, c-Jun failed to be upregulated correctly. Accordingly, a c-Jun binding motif was found to be enriched in promoters of genes with reduced expression in injured mutants. Furthermore, using cultured SCs, we found that mTORC1 is involved in c-Jun regulation by promoting its translation, possibly via the eIF4F-subunit eIF4A. These results provide evidence that proper c-Jun elevation after nerve injury involves also mTORC1-dependent post-transcriptional regulation to ensure timely dedifferentiation of SCs.ISSN:0270-6474ISSN:1529-240

Piezofibre composite transducers for next generation 3D USCT

At the Karlsruhe Institue of Technology (KIT), a 3D-Ultrasound Computer Tomography (3D-USCT) medical imaging system for early breast cancer detection is currently developed. With the next generation of 3D-USCT 2.5, the current region of interest (ROI) of 10 x 10 x 10 cm³ shall be increased to 20 x 20 x 20 cm³ to allow reliable imaging results also for bigger female breasts. Therefore, the opening angle (OA) of the future transducers should be increased to approx. 60 at 3 dB while other characteristics such as bandwidth (BW) and resonance frequency should be preserved or even improved. Based on Fraunhofer IKTS Piezofibre composites utilized for transducer production, an optimization is performed on piezoelectric sensor geometry and size, type and structure of matching and backing layer and interconnection technology of the several parts of the transducerImPhys/Acoustical Wavefield Imagin