The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events

The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m^3 and is operated in a 0.5 T solenoidal magnetic field parallel to its axis. In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb--Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report.Comment: 55 pages, 82 figure

The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events

The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m3 and is operated in a 0.5 T solenoidal magnetic field parallel to its axis. In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb–Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report.publishedVersio

Mechanical systems in the quantum regime

Mechanical systems are ideal candidates for studying quantumbehavior of macroscopic objects. To this end, a mechanical resonator has to be cooled to its ground state and its position has to be measured with great accuracy. Currently, various routes to reach these goals are being explored. In this review, we discuss different techniques for sensitive position detection and we give an overview of the cooling techniques that are being employed. The latter include sideband cooling and active feedback cooling. The basic concepts that are important when measuring on mechanical systems with high accuracy and/or at very low temperatures, such as thermal and quantum noise, linear response theory, and backaction, are explained. From this, the quantum limit on linear position detection is obtained and the sensitivities that have been achieved in recent opto and nanoelectromechanical experiments are compared to this limit. The mechanical resonators that are used in the experiments range from meter-sized gravitational wave detectors to nanomechanical systems that can only be read out using mesoscopic devices such as single-electron transistors or superconducting quantum interference devices. A special class of nanomechanical systems are bottom-up fabricated carbon-based devices, which have very high frequencies and yet a large zero-point motion, making them ideal for reaching the quantum regime. The mechanics of some of the different mechanical systems at the nanoscale is studied. We conclude this review with an outlook of how state-of-the-art mechanical resonators can be improved to study quantum {\it mechanics}.Comment: To appear in Phys. Re

Peptide microarray fabrication by laser-based in situ synthesis and utilization for infectious disease research

Due to the circulation of infectious diseases and the emergence of new pathogens, fundamental research, as well as the development of vaccines are of utmost importance. Peptide microarrays (PMAs) can facilitate the investigation of an immune response to an antigen by detecting linear B cell epitopes. They consist of a miniaturized spot pattern containing different peptide sequences. These reproduce all potential linear epitopes of a protein, usually as a map of overlapping peptides. Therefore, PMAs allow for high-throughput screening in a fast manner. To show their versatility, PMAs were applied for the detection of linear B cell epitopes elicited by infectious pathogens or a vaccine-delivered antigen. First, PMAs of the Ebola virus spike glycoprotein were used to analyze the development of antibodies, recognizing linear peptide epitopes, in vaccine recipients and an Ebola virus disease survivor. Second, PMAs covering the SARS-CoV-2 coronavirus proteome were used to identify epitopes. The antibodies elicited by patients with COVID-19 disease were studied during the course of the disease. Today, commercially available PMAs do either lack peptide sequence flexibility and/or a high peptide density. Thus, the price per analyzed sample is high and therefore, reducing the usage of PMAs. Hence, the combinatorial laser-induced forward transfer (cLIFT) technology was developed for the fabrication of high-density PMAs. Thereby, a polymer and an amino acid are transferred via laser irradiation from a donor to an acceptor in a spot pattern. Together with intermittent chemical processing, this laser based technique can be used to in situ synthesize microarrays. With the implementation of an automated synthesizer and optimal synthesis parameters, it was possible to produce up to 20-residue peptides with controlled spot size. Finally, a full combinatorial synthesis of overlapping 15-mer peptides containing the Ebola virus proteome with 4444 and 10 000 spots per cm2 was performed. The antibody binding was compared to a commercial peptide microarray containing the same peptides of the spike glycoprotein. The results revealed an excellent quality up to a density of 4444 spots per cm2. Moreover, the flexibility of this method allows the exchange of building blocks and thus, enables the synthesis of other molecules.Angesichts der Verbreitung von Infektionskrankheiten und dem Auftreten neuer Krankheitserreger sind Grundlagenforschung und die Entwicklung von Impfstoffen von größter Bedeutung. Peptid Microarrays (PMAs) können die Untersuchung einer Immunantwort auf ein Antigen durch den Nachweis linearer B-Zell-Epitope erleichtern. Sie bestehen aus einem miniaturisierten Spotmuster, welches verschiedene Peptidsequenzen enthält. Diese bilden alle potentiellen linearen Epitope eines Proteins ab, in der Regel als überlappende Peptide. Daher ermöglichen PMAs schnelle Hochdurchsatz-Untersuchungen. Um ihre Vielseitigkeit zu zeigen, wurden PMAs für den Nachweis linearer B-Zelle-Epitope eingesetzt, die durch infektiöse Erreger oder durch ein Impfstoff-verabreichtes Antigen ausgelöst wurden. Zuerst wurden PMAs des Ebolavirus Spike-Glykoproteins verwendet, um die Entwicklung von Antikörpern, welche lineare Peptidepitope erkennen, in Geimpften und einem Überlebenden der Ebolavirus Erkrankung zu analysieren. Zweitens wurden PMAs, die das Proteom des Coronavirus SARS-CoV 2 umfassen, zur Identifizierung von Epitopen eingesetzt. Somit konnten die gebildeten Antikörper von Patienten mit der COVID-19-Erkrankung im Verlauf der Erkrankung untersucht werden. Heutzutage, mangelt es kommerziell erhältlichen PMAs entweder an Peptidsequenzflexibilität und/oder an hoher Peptiddichte. Dadurch ist der Preis pro analysierter Probe hoch und schränkt somit die Anwendung von PMAs ein. Daher wurde der kombinatorische Laser-induzierte Vorwärtstransfer (cLIFT) zur Herstellung von PMAs mit hoher Dichte entwickelt. Dabei werden Spots, die ein Polymer und eine Aminosäure enthalten, von einem Donator auf einen Akzeptor übertragen, um ein Spotmuster zu erzeugen. Zusammen mit intermittierenden chemischen Schritten kann diese Laser-basierte Technik zur in situ Synthese von Microarrays verwendet werden. Mit der Einführung einer automatisierten Synthesemaschine und optimaler Syntheseparameter war es möglich Peptide mit bis zu 20 Aminosäuren und kontrollierter Spotgröße herzustellen. Schließlich wurde eine vollständig kombinatorische Synthese von überlappenden 15-mer Peptiden, die das Proteom des Ebolavirus umfassen, mit 4444 und 10 000 Spots pro cm2 durchgeführt. Die Antikörperbindung wurde mit einem kommerziellen Peptid Microarray verglichen, der die gleichen Peptide des Spike-Glykoproteins enthält. Die Ergebnisse zeigten eine hervorragende Qualität bis zu einer Dichte von 4444 Spots pro cm2. Darüber hinaus ermöglicht die Flexibilität dieser Methode den Austausch von Bausteinen und damit die Synthese anderer Moleküle

Graphene mechanical resonators coupled to superconducting microwave cavities

In recent years, mechanical resonators based on graphene have attracted considerable interest as nanoelectromechanical systems (NEMS). Graphene NEMSs allow for exceptional properties such as high mechanical strength, high frequencies and quality factors, tunable mechanical properties, and ultra-low mass. As a consequence, these systems are promising to investigate motion in the quantum regime, probe rich nonlinear phenomena, sense minuscule masses and forces, and study surface science. However, a central challenge in graphene NEMS research is the coupling of the mechanical vibrations to external systems for efficient read out and manipulation. In this dissertation, we report on a novel approach, in which we harness the optomechanical radiation pressure interaction to investigate few-layer and multilayer graphene mechanical resonators at cryogenic temperatures (T = 15 mK). The capacitive coupling between graphene mechanical systems and the microwave photons of a superconducting microwave cavity allows for investigation of the mechanical properties with unprecedented accuracy and control. In a first experiment, the coupling of circular, high-Q graphene mechanical resonators (Qm ~105) to a nearby cavity counter electrode results in a large single-photon optomechanical coupling of ~10 Hz. The initial devices exhibit electrostatic tunability of the graphene equilibrium position, strong tunability of the mechanical resonance frequency, and the possibility to control the sign and magnitude of the observed During nonlinearity. Compared to optomechanical systems fabricated from bulk materials, the strong tunability of the mechanical properties of graphene NEMS is unique. In a second experiment, we quantitatively investigate the sideband cooling and force sensing performance of multilayer graphene optomechanical systems. The strong coupling to the microwave photons allows to achieve a mechanical displacement sensitivity of 1:3 fm Hz-1/2 and to cool the mechanical motion to an average phonon occupation of 7:2. In terms of force sensing performance, we find that the force sensitivity is limited by the imprecision in the measurement of the vibrations, the fluctuations of the mechanical resonant frequency, and the heating induced by the measurement. Our best force sensitivity, 390 zN Hz-1/2, is achieved by balancing measurement imprecision, optomechanical damping, and Joule heating. These results hold promise for studying the quantum capacitance of graphene, its magnetization, and the electron and nuclear spins of molecules adsorbed on its surface. In a third experiment, we implement energy decay measurements to study mechanical dissipation processes in multilayer graphene mechanical resonators. We study the energy decay in two regimes. In the low-amplitude regime, the mechanical quality factor surpasses Qm = 106. This quality factor is larger than that obtained with spectral measurements, because energy decay measurements are immune from dephasing. In the high-amplitude regime, the motion of atomically-thin mechanical resonators is radically different from what has been observed in other resonators thus far. Instead of a smooth exponential decay, energy decays discontinuously, that is, the dissipation rate increases step like above a certain threshold amplitude. We attribute these phenomena to nonlinear decay processes. These findings offer new opportunities for manipulating vibrational states.Durante los últimos años resonadores mecánicos basados en grafeno han atraído un considerable interés como sistemas nanoelectromecánicos (NEMS). Los NEMS de grafeno permiten excepcionales propiedades como una gran estabilidad mecánica, altas frecuencias de resonancia y factores de calidad, propiedades mecánicas ajustables y masas muy pequeñas. Como consecuencia, estos sistemas son buenos candidatos para investigar el movimiento mecánico en el régimen cuántico, indagar varios fenómenos no lineales, medir minúsculas masas o fuerzas y estudiar los efectos de superficie. Sin embargo, el mayor reto en la investigación de los NEMS de grafeno es el acoplamiento de las vibraciones mecánicas con sistemas externos con el objetivo de hacer una manipulación y lectura eficiente. En esta tesis, presentamos un nuevo enfoque en el cual aprovechamos la interacción de la presión de radiación optomecánica para investigar resonadores mecánicos de grafeno compuesto de pocas capas y multicapas en temperaturas criogénicas (T = 15 mK). El acoplamiento capacitivo entre el sistema mecánico de grafeno y los fotones de microondas de una cavidad superconductora permite la investigación de las propiedades mecánicas con una precisión y control sin precedentes. En un primer experimento el acoplamiento de un resonador circular de grafeno con un alto factor Q con un electrodo de la cavidad da como resultado un gran acoplamiento optomecánico de 10 Hz. Los dispositivos iniciales muestran un ajustamiento electrostático de la posición de equilibrio del grafeno, una fuerte variabilidad de la frecuencia de resonancia mecánica y la posibilidad de controlar el signo y magnitud de la no linearidad de tipo Dung. Comparado con otros sistemas optomecánicos fabricados de materiales bulk, la gran variabilidad de las propiedades mecánicas es única en los NEMS de grafeno. En un segundo experimento investigamos cuantitativamente el enfriamiento fuera de banda y sensibilidad de fuerzas usando un sistema optomecánico basado en grafeno multicapa. El fuerte acoplamiento a los fotones de microondas nos permite conseguir una sensibilidad del desplazamiento mecánico de 1:3 fm Hz-1/2 y también enfriar el movimiento mecánico hasta una ocupación media de 7:2 fonones. En términos de sensor de fuerzas, encontramos que la sensibilidad de fuerzas está limitada por la imprecisión en la medida de las vibraciones, las fluctuaciones de la frecuencia de resonancia mecánica y en el calentamiento inducido por la medida. Nuestra mejor sensibilidad de fuerzas 390 zN Hz-1/2 se consigue ajustando la imprecisión de la medida, el decaimiento optomecánico y el calentamiento Joule. Estos resultados son prometedores para el estudio de las capacidades cuánticas del grafeno, su magnetización y los espines nucleares y electrónicos de moléculas adsorbidas en la superficie del grafeno. En un tercer experimento implementamos medidas del decaimiento de energía para estudiar los procesos de disipación mecánica en resonadores de grafeno en multicapa

Capacitive ultrasonic transducers fabricated using microstereolithography

Air-coupled thin-membrane capacitive ultrasonic transducers have been developed that use microstereolithography fabrication with architectures comprised entirely of partially metalised photopolymer. These devices derive considerable advantages from rapid prototyping technology, in that they are cheap to produce, and benefit from the design-to-product lead times inherent in the production of components using stereolithography. To date membranes have been produced with thicknesses ranging from 30 to 90 μm with aspect ratios in the range of 100 - 1000. These devices have been shown to operate both as transmitters and as receivers of ultrasound, and have a bandwidth approaching 100% with a centre frequency of 100 kHz. The method of fabricating these devices allows for easy modification for various applications including structural health monitoring and immersion, as well as affording the possibility of integrated focussing or wave-guiding architecture and packaging that can be incorporated into a single build. Fundamental or subtle changes to a given transducer design may be achieved incurring little additional cost or time. This novel approach to transducer fabrication enables the bespoke manufacture of specific transducer architectures from a computer aided design package using polymers that exhibit different material properties to materials used in silicon micromachining, but at the same time allow for fabrication on a scale that is approaching that of microfabrication. The versatility of 3-D rapid prototyping allows the realisation of more complicated structures than was possible previously. This work examines these transducers in terms of their characterisation and their operation in conjunction with other transduction architecture, such as focussing parabolic mirrors that were also produced using the same manufacturing technology. In addition, their operation in contacting acoustics and the reception of surface acoustic waves has been demonstrated. Immersion studies using these devices have found that that they hold promise for operation in a variety of different media. These transducers are seen as an important prototype development tool in the field of capacitive ultrasonic transduction and microphone-speaker design

Design and construction of a fibre interferometer for the study of MEMS and NEMS to temperatures below 1 K

Optical interferometry offers a powerful tool for the study of the mechanical motion of micro- and nano-electromechanical systems (MEMS and NEMS). By examining the modulation of reflected light the displacement can be measured with sub-nanometre precision. Recent work with fibre interferometers carried out by other groups has studied the motion of nanomechanical systems down to temperatures as low as 1 K. Dissipation measurements in the last few years of a number of devices fabricated from high-stress amorphous silicon nitride have shown a marked increase in quality factors when compared to similar low-stress devices. The high quality factors and small masses of these devices have attracted a great deal of interest within the nanomechanical and optomechanical communities. Measurements of dissipation in nanomechanical resonators carried out in Nottingham to date have used the magnetomotive effect to detect nanomechanical motion. This has required that a layer of metal be applied to the high-stress silicon nitride, modifying the mechanical properties. In this thesis we present an overview of the design and construction of an optical detection system designed to study MEMS and NEMS devices from room temperature to liquid helium temperatures. Optical detection is able to measure the displacement of purely dielectric structures and as such is an ideal method with which to measure dissipation in these high-Q silicon nitride resonators, complementing the other nanomechanical measurement techniques available within Nottingham. Using this system, measurements have been made on a number of micro- and nano-electromechanical systems fabricated using processes developed during this work. Confocal images of these devices obtained using the fibre interferometer show a spatial resolution of 0.75 um, a value close to the diffraction limit of the system. Micromechanical quartz tuning forks have been measured to confirm the frequency response of the interferometer, with a value for the piezo-electro-mechanical coupling constant of 2.18 +/- 0.06 uC/m obtained that is in very good agreement with the values published in the literature. Nanomechanical measurements of 200 um square high-stress silicon nitride membranes have revealed thermoelastic damping to be the limiting dissipation mechanism for these resonators at room temperature. Using elastic theory it is possible to quantify the fQ floor predicted by thermoelastic damping seeing good agreement with experimental data. At lower temperatures inter-membrane coupling was observed, with acoustic vibrations from neighbouring membranes coupling into and being amplified by the membrane under observation. Discrepancies in quality factor between the observed and unobserved membranes are most likely due to optomechanical damping of the observed membrane by the laser. This inter-membrane coupling offers a powerful technique for the indirect observation of the flexural modes of nearby membranes without optically damping the response

Nonlinear mechanics and nonlinear material properties in micromechanical resonators

Microelectromechanical Systems are ubiquitous in modern technology, with applications ranging from accelerometers in smartphones to ultra-high precision motion stages used for atomically-precise positioning. With the appropriate selection of materials and device design, MEMS resonators with ultra-high quality factors can be fabricated at minimal cost. As the sizes of such resonators decrease, however, their mechanical, electrical, and material properties can no longer be treated as linear, as can be done for larger-scale devices. Unfortunately, adding nonlinear effects to a system changes its dynamics from exactly-solvable to only solvable in specific cases, if at all. Despite (and because of) these added complications, nonlinear effects open up an entirely new world of behaviors that can be measured or taken advantage of to create even more advanced technologies. In our resonators, oscillations are induced and measured using aluminum nitride transducers. I used this mechanism for several separate highly-sensitive experiments. In the first, I demonstrate the incredible sensitivity of these resonators by actuating a mechanical resonant mode using only the force generated by the radiation pressure of a laser at room temperature. In the following three experiments, which use similar mechanisms, I demonstrate information transfer and force measurements by taking advantage of the nonlinear behavior of the resonators. When nonlinear resonators are strongly driven, they exhibit sum and difference frequency generation, in which a large carrier signal can be mixed with a much smaller modulation to produce signals at sum and difference frequencies of the two signals. These sum and difference signals are used to detect information encoded in the modulation signal using optical radiation pressure and acoustic pressure waves. Finally, in my experiments, I probe the nonlinear nature of the piezoelectric material rather than take advantage of the nonlinear resonator behavior. The relative sizes of the linear and nonlinear portions of the piezoelectric constant can be determined because the force applied to the resonator by a transducer is independent of the dielectric constant. This method allowed me to quantify the nonlinear constants

Capacitive ultrasonic transducers fabricated using microstereolithography

Air-coupled thin-membrane capacitive ultrasonic transducers have been developed that use microstereolithography fabrication with architectures comprised entirely of partially metalised photopolymer. These devices derive considerable advantages from rapid prototyping technology, in that they are cheap to produce, and benefit from the design-to-product lead times inherent in the production of components using stereolithography. To date membranes have been produced with thicknesses ranging from 30 to 90 μm with aspect ratios in the range of 100 - 1000. These devices have been shown to operate both as transmitters and as receivers of ultrasound, and have a bandwidth approaching 100% with a centre frequency of 100 kHz. The method of fabricating these devices allows for easy modification for various applications including structural health monitoring and immersion, as well as affording the possibility of integrated focussing or wave-guiding architecture and packaging that can be incorporated into a single build. Fundamental or subtle changes to a given transducer design may be achieved incurring little additional cost or time. This novel approach to transducer fabrication enables the bespoke manufacture of specific transducer architectures from a computer aided design package using polymers that exhibit different material properties to materials used in silicon micromachining, but at the same time allow for fabrication on a scale that is approaching that of microfabrication. The versatility of 3-D rapid prototyping allows the realisation of more complicated structures than was possible previously. This work examines these transducers in terms of their characterisation and their operation in conjunction with other transduction architecture, such as focussing parabolic mirrors that were also produced using the same manufacturing technology. In addition, their operation in contacting acoustics and the reception of surface acoustic waves has been demonstrated. Immersion studies using these devices have found that that they hold promise for operation in a variety of different media. These transducers are seen as an important prototype development tool in the field of capacitive ultrasonic transduction and microphone-speaker design.EThOS - Electronic Theses Online ServiceGBUnited Kingdo