Study and development of UV photodetectors envisaging COMPASS RICH-1 upgrade and applications

COMPASS is an experiment at CERN’s SPS whose goal is to study hadron structure and spectroscopy. The experiment includes a wide acceptance RICH detector, operating since 2001 and subject to a major upgrade of the central region of its photodetectors in 2006. The remaining 75% of the photodetection area are still using MWPCs from the original design, who suffer from limitations in gain due to aging of the photocathodes from ion bombardment and due to ion-induced instabilities. Besides the mentioned limitations, the increased luminosity conditions expected for the upcoming years of the experiment make an upgrade to the remaining detectors pertinent. This upgrade should be accomplished in 2016, using hybrid detectors composed of ThGEMs and MICROMEGAS. This work presents the study, development and characterization of gaseous photon detectors envisaging the foreseen upgrade, and the progress in production and evaluation techniques necessary to reach increasingly larger area detectors with the performances required. It includes reports on the studies performed under particle beam environment of such detectors. MPGD structures can also be used in a variety of other applications, of which nuclear medical imaging is a notorious example. This work includes, additionally, the initial steps in simulating, assembling and characterizing a prototype of a gaseous detector for application as a Compton Camera.

Design of a speed meter interferometer proof-of-principle experiment

The second generation of large scale interferometric gravitational wave (GW) detectors will be limited by quantum noise over a wide frequency range in their detection band. Further sensitivity improvements for future upgrades or new detectors beyond the second generation motivate the development of measurement schemes to mitigate the impact of quantum noise in these instruments. Two strands of development are being pursued to reach this goal, focusing both on modifications of the well-established Michelson detector configuration and development of different detector topologies. In this paper, we present the design of the world's first Sagnac speed meter (SSM) interferometer, which is currently being constructed at the University of Glasgow. With this proof-of-principle experiment we aim to demonstrate the theoretically predicted lower quantum noise in a Sagnac interferometer compared to an equivalent Michelson interferometer, to qualify SSM for further research towards an implementation in a future generation large scale GW detector, such as the planned Einstein telescope observatory.

Bayesian statistics for the calibration of the LISA Pathfinder experiment

The main goal of LISA Path finder (LPF) mission is to estimate the acceleration noise models of the overall LISA Technology Package (LTP) experiment on-board. This will be of crucial importance for the future space-based Gravitational-Wave (GW) detectors, like eLISA. Here, we present the Bayesian analysis framework to process the planned system identification experiments designed for that purpose. In particular, we focus on the analysis strategies to predict the accuracy of the parameters that describe the system in all degrees of freedom. The data sets were generated during the latest operational simulations organised by the data analysis team and this work is part of the LTPDA Matlab toolbox.

Superconducting Transition-Edge Sensor Physics

Despite record-setting performance demonstrated by superconducting Transition Edge Sensors (TESs) and growing utilization of the technology, a theoretical model of the physics governing TES devices superconducting phase transition has proven elusive. Earlier attempts to describe TESs assumed them to be uniform superconductors. Sadleir et al. 2010 shows that TESs are weak links and that the superconducting order parameter strength has significant spatial variation. Measurements are presented of the temperature T and magnetic field B dependence of the critical current Ic measured over 7 orders of magnitude on square Mo/Au bilayers ranging in length from 8 to 290 microns. We find our measurements have a natural explanation in terms of a spatially varying order parameter that is enhanced in proximity to the higher transition temperature superconducting leads (the longitudinal proximity effect) and suppressed in proximity to the added normal metal structures (the lateral inverse proximity effect). These in-plane proximity effects and scaling relations are observed over unprecedentedly long lengths (in excess of 1000 times the mean free path) and explained in terms of a Ginzburg-Landau model. Our low temperature Ic(B) measurements are found to agree with a general derivation of a superconducting strip with an edge or geometric barrier to vortex entry and we also derive two conditions that lead to Ic rectification. At high temperatures the Ic(B) exhibits distinct Josephson effect behavior over long length scales and following functional dependences not previously reported. We also investigate how film stress changes the transition, explain some transition features in terms of a nonequilibrium superconductivity effect, and show that our measurements of the resistive transition are not consistent with a percolating resistor network model.

Free-flight experiments in LISA Pathfinder

The LISA Path finder mission will demonstrate the technology of drag-free test masses for use as inertial references in future space-based gravitational wave detectors. To accomplish this, the Path finder spacecraft will perform drag-free flight about a test mass while measuring the acceleration of this primary test mass relative to a second reference test mass. Because the reference test mass is contained within the same spacecraft, it is necessary to apply forces on it to maintain its position and attitude relative to the spacecraft. These forces are a potential source of acceleration noise in the LISA Path finder system that are not present in the full LISA con figuration. While LISA Path finder has been designed to meet it's primary mission requirements in the presence of this noise, recent estimates suggest that the on-orbit performance may be limited by this 'suspension noise'. The drift-mode or free-flight experiments provide an opportunity to mitigate this noise source and further characterize the underlying disturbances that are of interest to the designers of LISA-like instruments. This article provides a high-level overview of these experiments and the methods under development to analyze the resulting data.

In-flight thermal experiments for LISA Pathfinder: Simulating temperature noise at the Inertial Sensors

Thermal Diagnostics experiments to be carried out on board LISA Pathfinder (LPF) will yield a detailed characterisation of how temperature fluctuations affect the LTP (LISA Technology Package) instrument performance, a crucial information for future space based gravitational wave detectors as the proposed eLISA. Amongst them, the study of temperature gradient fluctuations around the test masses of the Inertial Sensors will provide as well information regarding the contribution of the Brownian noise, which is expected to limit the LTP sensitivity at frequencies close to 1mHz during some LTP experiments. In this paper we report on how these kind of Thermal Diagnostics experiments were simulated in the last LPF Simulation Campaign (November, 2013) involving all the LPF Data Analysis team and using an end-to-end simulator of the whole spacecraft. Such simulation campaign was conducted under the framework of the preparation for LPF operations.

Ocratoxina A e citrinina em arroz: um estudo de metodologia para determinação simultânea de ocorrência

A ocratoxina A e a citrinina são micotoxinas encontrados naturalmente em alimentos e rações animais. A avaliação do risco do consumo de alimentos contaminados por esses compostos deve ser estimada a partir de dados confiáveis que reflitam a verdadeira concentração destas toxinas em diferentes alimentos ou insumos, especialmente se ingeridos com freqüência. Isto gera a necessidade de métodos analíticos precisos que sejam rápidos sem desconsiderar as etapas clássicas de avaliação de traços, amostragem representativa, extração, limpeza, concentração, separação de formas químicas, detecção, confirmação de identidade e quantificação. Para as micotoxinas em geral as técnicas cromatográficas são as mais aplicadas e relatadas em vista da diversidade estrutural destes compostos. Neste trabalho foi realizada uma otimização de extração utilizando o método QuEChERS modificado em comparação com os métodos Soares e Rodrigues Amaya (1989), Tanaka (2001) e Ultrassom (Palma et. al., 2007) empregando diferentes técnicas cromatográficas com detectores distintos para análise destas micotoxinas simultaneamente. Foram analisadas 38 amostras de arroz cultivadas e armazenadas em campos experimentais de Cachoeirinha na região Sul do Brasil. O uso dos sistemas CCD, HPLC-DAD e LC-MS proporcionou especificidade, precisão e sensibilidade, de modo que os limites de detecção e quantificação, obtivessem valores inferiores ao limite máximo estabelecido por órgãos reguladores internacionais (5 µg Kg-1 para ocratoxina A). Os limites de detecção encontrados para citrinina e ocratoxina A em camada delgada foram 4,7 e 6 vezes maior que para cromatografia líquida de alta eficiência acoplada a detector de arranjo de diodos, 14 e 300 vezes maior que cromatografia líquida acoplada a detector de massas. Os limites de quantificação das duas micotoxinas ficaram dentro do exigido pela legislação européia para OTA de 5 µg Kg-1 para HPLC-DAD e LC-MS. Na cromatografia de camada delgada esse valor ficou 4 vezes acima do estabelecido para ocratoxina A. A ocorrência de ocratoxina A e citrinina foi verificada em 16 % das amostras estando os teores variando entre 3 e 560 µg Kg-1, sugerindo possível exposição crônica a estas micotoxinas caso as amostras sejam consumidas.

Calibration and simulations of SIXS-P's response to energetic particles

The Solar Intensity X-ray and particle Spectrometer (SIXS) on board BepiColombo's Mercury Planetary Orbiter (MPO) will study solar energetic particles moving towards Mercury and solar X-rays on the dayside of Mercury. The SIXS instrument consists of two detector sub-systems; X-ray detector SIXS-X and particle detector SIXS-P. The SIXS-P subdetector will detect solar energetic electrons and protons in a broad energy range using a particle telescope approach with five outer Si detectors around a central CsI(Tl) scintillator. The measurements made by the SIXS instrument are necessary for other instruments on board the spacecraft. SIXS data will be used to study the Solar X-ray corona, solar flares, solar energetic particles, the Hermean magnetosphere, and solar eruptions. The SIXS-P detector was calibrated by comparing experimental measurement data from the instrument with Geant4 simulation data. Calibration curves were produced for the different side detectors and the core scintillator for electrons and protons, respectively. The side detector energy response was found to be linear for both electrons and protons. The core scintillator energy response to protons was found to be non-linear. The core scintillator calibration for electrons was omitted due to insufficient experimental data. The electron and proton acceptance of the SIXS-P detector was determined with Geant4 simulations. Electron and proton energy channels are clean in the main energy range of the instrument. At higher energies, protons and electrons produce non-ideal response in the energy channels. Due to the limited bandwidth of the spacecraft's telemetry, the particle measurements made by SIXS-P have to be pre-processed in the data processing unit of the SIXS instrument. A lookup table was created for the pre-processing of data with Geant4 simulations, and the ability of the lookup table to provide spectral information from a simulated electron event was analysed. The lookup table produces clean electron and proton channels and is able to separate protons and electrons. Based on a simulated solar energetic electron event, the incident electron spectrum cannot be determined from channel particle counts with a standard analysis method.