Design, scale-up and characterization of the data acquisition system for the ANAIS dark matter experiment

El proyecto ANAIS, iniciado en los noventa, se ha dedicado a desarrollar un experimento de materia oscura con ioduro de sodio en el Laboratorio Subterráneo de Canfranc (LSC) y podría confirmar el resultado positivo de DAMA/LIBRA usando la misma técnica y el mismo material blanco. Un experimento de estas características posee unos requisitos muy estrictos para tener sensibilidad suficiente a la modulación anual: tener el menor fondo radioactivo posible en la zona de interés, poseer un umbral energético muy bajo y tener suficiente masa. Además de estos requisitos fundamentales es necesaria una muy buena estabilidad en la adquisición de datos y un buen control de los parámetros ambientales para evitar que posibles efectos sistemáticos puedan ser tomados por modulación anual de materia oscura. El experimento ANAIS constará de más de cien kilogramos de ioduro de sodio ultrapuro en proceso de fabricación y que serán instalados en los próximos meses en el LSC. Esta tesis ha estado enfocada al diseño, implementación y caracterización de un sistema de adquisición de datos adecuado para el experimento ANAIS teniendo en cuenta los requisitos antes mencionados. Se han estudiado los fotomultiplicadores (PMTs) elegidos para la detección de la luz del centelleo del ioduro de sodio. Además se han desarrollado los algoritmos y protocolos necesarios para hacer el control de calidad de todas la unidades. Se ha descrito el diseño de la electrónica necesaria para la adquisición de datos de los módulos de ioduro y los centelladores plásticos usados como detector de muones junto con el software de adquisición y de análisis de datos. También se ha medido la recogida de luz de tres módulos de Alpha Spectra, los dos primeros de que constó el prototipo ANAIS-25 y un tercero que unido a los dos anteriores formaron ANAIS-37. Por último, se ha hecho un estudio de la estabilidad de los parámetros ambientales y de parámetros cruciales para la adquisición de datos.The ANAIS project has been a long time effort devoted to carry out an experiment to detect dark matter annual modulation with very low background NaI(Tl) detectors. This experiment could confirm the DAMA/LIBRA positive signal with the same target and technique. Such an experiment has a very stringent requirements in order to have enough sensitivity to an annual modulation at very low energy. These requirements are: very low energy threshold, a background as low as possible in the region of interest and a high enough target mass. In addition to these fundamental requirements, very good stability and control of environmental parameters have to be accomplished in order to avoid systematic effects to mimic the effect of the annual modulation. An experiment of more than one hundred kilograms of ultrapure NaI(Tl) has been conceived and it is being commissioned at the Canfranc Underground Laboratory (LSC). This work was devoted to the design, implementation and characterization of a data acquisition system suitable for the ANAIS experiment, having in mind the previously mentioned requirements. It has described the Photomultiplier Tubes (PMTs) used by the ANAIS modules and the algorithms and protocol developed in order to pass quality tests to all units. It has presented the design and implementation of the electronic front-end for the ANAIS modules and muon tagging system along with the data acquisition software. The analysis software was adapted from the software of the previous prototypes to allow easy scale-up to the full experiment. Finally, the test of the optical performance of the Alpha Spectra modules and the tests of data acquisition and monitoring of environmental parameters were performed

Optical quantum random number generation: applications of single-photon event timing

This dissertation is the result of research which, although electrical and computer engineering in nature, also aims to improve the performance of many systems in the field of quantum information. For example, random number generators are used in almost all areas of science, and the initial portion of this work details the theory, design, and characterization of two photon-arrival-time quantum random number generators (QRNGs). After the QRNGs were completed, it was realized that their performance was severely limited both by the maximum detection rate of the single-photon detectors used, and the precision at which the arrival times could be resolved. The single-photon detectors used for both QRNGs are single-photon avalanche photodiodes (SPADs), devices which when operated below their breakdown voltage can create a macroscopic amount of current (an avalanche) in response to a single incident photon. Some of this charge can become trapped in defects or impurities; if this trapped charge is released when the SPAD is active, a secondary ‘false’ detection event, or ‘afterpulse’ can occur. To lower the afterpulse probability to reasonable levels (< 1%), we attempted to reduce the amount of avalanche charge by halting its growth promptly with high-speed electronics, so that defects have a lower probability of becoming populated in the first place. Initial results show reductions in afterpulse probability by up to a factor of 12, corresponding to a ~20% decrease in dead time, a value that could be improved further. We developed an FPGA-based time-to-digital converter system for use specifically with SPADs, achieving a time-bin resolution of 100 ps, with lower dead time and higher maximum detection rate than all currently available detection systems. This further allowed for the creation of a new higher-order SPAD characterization technique, which was identified previously unknown subtleties to SPAD operation. Finally, we developed an ultra-low-latency QRNG, which was used in one of the recent loophole-free demonstrations of quantum nonlocality. The final latency was below 2.5 ns, to our knowledge the lowest latency QRNG to date. Of special interest, however, is our subsequent exploration into the characterization of its bit-probability drift using atomic clock stability techniques. By employing the Allan deviation and implementing precision feedback, the additional frequency drift caused by environmental fluctuations is reduced such that the resulting bit stream can pass cryptographic random number tests for sample sizes up to 5 Gb. This system is currently intended for the NIST random-number beacon, a world-wide trusted source of random bits