SuperCDMS is a leading direct dark matter search experiment which uses solid state detectors (Ge crystals) at milliKelvin temperatures to look for nuclear recoils caused by dark matter interactions in the detector. ‘Weakly Interacting Massive Particles’ (WIMPs) are the most favoured dark matter candidate particles. SuperCDMS, like many other direct dark matter search experiments, primarily looks for WIMPs. The measurement of both the ionization and the lattice vibration (phonon) signals from an interaction in the detector allow it to discriminate against electron recoils which are the main source of background for WIMP detection. SuperCDMS currently operates about 9 kgs worth of germanium detectors at the Soudan underground lab in northern Minnesota. In its next phase, SuperCDMS SNOLAB, it plans to use 100-200 kg of target mass (Ge) which would allow it to probe more of the interesting and unexplored parameter space for WIMPs predicted by theoretical models. The SuperCDMS Queen’s Test Facility is a detector testing facility which is intended to serve detector testing and detector research and development purposes for the SuperCDMS experiment. A modified detector called the ‘HiZIP’ (Half-iZIP), which is reduced in complexity in comparison to the currently used iZIP (interleaved Z-sensitive Ionization and Phonon mediated) detectors, is studied in this thesis. The HiZIP detector design also serves to discriminate against background from multiple scatter events occurring close to the surfaces in a single detector. Studies carried out to compare the surface event leakage in the HiZIP detector using limited information from iZIP data taken at SuperCDMS test facility at UC Berkley produce a highly conservative upper limit of 5 out of 10,000 events at 90% confidence level. This upper limit is the best among many different HiZIP configurations that were investigated and is comparable to the upper limit calculated for an iZIP detector in the same way using the same data. A real HiZIP device operated at Queen’s Test Facility produced an exposure limited 90% upper limit of about 1 in 100 events for surface event leakage. The data used in these studies contain true nuclear recoil events from cosmogenic and ambient neutrons. This background was not subtracted in the calculation of the upper limits stated above and hence they are highly conservative. A surface event source was produced by depositing lead-210 from radon exposure onto a copper plate. This source was then used to take data for a surface event discrimination study of the HiZIP detector operated at Queen’s Test Facility. A study of the contribution of the noise from capacitive crosstalk between charge sensors in a HiZIP detector configuration was investigated, confirming the expectation that no significant drop in performance is to be expected due to this effect. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-30 23:48:49.375

The EDELWEISS experiment is one of the dark matter direct detection experiments. It aims to detect WIMP interactions using an array of cryogenic germanium detectors. In the previous EDELWEISS-II phase, the cables and connectors used have been identified as a major source of neutron background in the experiment, which means that further effort aimed at better WIMP-nucleon interaction detection sensitivity requires a new, different cold cabling solution connecting the detectors to the front-end electronics. Motivated by this, a new two-section cold cabling system based on semi-flexible laminated copper and stainless steel cables has been developed for the EDELWEISS- III phase at Oxford. Batches of prototypes have been tested first in a cryostat at Oxford as part of a phonon-scintillation detector module, and then at the LSM underground laboratory in several EDELWEISS-III commissioning runs. Following that, a final set of cabling has been produced and installed in the EDELWEISS-III setup, which is currently conducting a science run aiming to improve its sensitivity reach compared to the previous results. This new cold cabling system has shown similar electrical performance as the previous coaxial cabling when comparing different cold cabling configurations in a commissioning run at LSM. Also, its background contribution is within the EDELWEISS-III requirements, according to radioactivity level tests and Monte Carlo simulations. In addition, the assembled connectors have allowed hundreds of signal tracks to be installed within a few days and the low material and space budget has made the cables compatible with the compact cryostat design. Besides reading out detectors for dark matter detection, prototypes of this cabling solution for a wider application range have also been produced at Oxford. The next generation dark matter direct detection experiments aim to achieve detection sensitivity better by a few orders of magnitude. This requires a target mass at tonne-scale, which converts to thousands of cryogenic detectors. Cryogenic phonon-scintillation detectors used in current dark matter searches can provide excellent performance but they usually require individual tuning and attention, making operation in large-scale experiments difficult. It is also technically challenging to stably produce such detectors in large quantity. Therefore, a scalable, robust novel detector concept for cryogenic phonon- scintillation detectors to be used in future rare event search experiments has been developed in this work. This detector module consists of a phonon detector based on a CaMoO4 scintillating crystal as the target with an attached NTD-Ge sensor as the thermometer, and a light detector based on a low-temperature PMT. To provide the high voltage necessary for PMT operation while ensuring the detector module can be cooled down and that the performance of the phonon detector is unaffected, a high voltage supply system based on a Cockcroft-Walton generator (CWG), a transformer and a small AC input has been designed and tested in the cryostat. The laminated cabling system is chosen for reading out the phonon channel and connecting the CWG and the PMT. A test run has demonstrated that, the high voltage can be provided to the PMT without causing a problem to the detector operation, and it is feasible to operate the low-temperature PMT at a temperature as low as 17 mK. Testing with a cobalt-57 gamma source, the phonon detector and the light detector have achieved resolutions of 1.07 keV and 34.2 keV for the 122.06 keV peak respectively. This is close to the performance of detectors used in the current dark matter direct searches, proving this detector concept can be applied to future large-scale dark matter direct detection experiments and other rare event searches. Using the light channel in this detector setup, the scintillation properties of CaMoO4 has been studied. In this work, the experimental data of its scintillation decay time constant has been extended from the previous 7 K to milli-Kelvin temperatures. The data are interpreted using a three-level model, confirming the existence of a metastable emission level in CaMoO4, and giving various parameters of its emission centre. This suggests that the work related to producing a high voltage supply and demonstrating the excellent performance of a low-temperature PMT could also be attractive to scintillator studies at cryogenic temperatures.

Au cours des dernières décennies, l’observation du ciel dans les longueurs d’onde millimétriques a permis de faire grandement progresser notre compréhension de l’univers, notamment à travers l’étude du fond diffus cosmologique. Pour répondre aux besoins actuels des astronomes, nous proposons dans ce rapport un instrument intégré permettant de réaliser des mesures spectrales large-bande dans le domaine millimétrique. Celui-ci se base sur le concept de SWIFTS (Stationary-Wave Fourier-Transform Spectrometer :spectromètre de Fourier à ondes stationnaire), un instrument opérationnel aux longueurs d’onde visibles et infrarouges. Notre dispositif " SWIFTS millimétrique " utilise des détecteurs à inductance cinétique (KID pour Kinetic Inductance Detectors) comme détecteurs de lumière. Différents aspects de la conception du SWIFTS millimétrique sont abordés dans ce rapport. Le dimensionnement des éléments clés du dispositif est réalisé à l’aide de simulations électromagnétiques. Nous proposons aussi un procédé de fabrication en technologie silicium permettant le dépôt d’antennes sur membrane de nitrure de silicium SiN. Les premières caractérisations permettent de confirmer un fonctionnement adapté des détecteurs en configuration SWIFTS et démontre l’existence d’un couplage entre l’antenne et un des détecteurs aux longueurs d’onde millimétriques ce qui ouvre la voie à un futur démonstrateur. Parallèlement, la technologie développée pour le SWIFTS millimétrique a rendu possible la fabrication de KID sur membrane. L’intérêt est ici d’évaluer la membrane comme un moyen de réduire l’interaction entre les rayons cosmiques et le détecteur dans la perspective d’une utilisation des KID dans l’espace. Des mesures comparatives effectuées sur KID déposés sur membrane et sur substrat démontrent des taux d'événements identiques dans les deux cas. La membrane est donc inefficace pour l’application envisagée. Le temps de relaxation présente en revanche une dépendance avec la présence du substrat. / For the last decades, millimeter wavelength observations allowed a large improvement of our knowledge of the universe in particular with the study of the Cosmic Microwave Background. To meet today astronomers’ needs, we propose hereby an integrated instrument able to perform wide-band spectral measurements in the millimeter spectrum. It is based on the SWIFTS concept (Stationary-Wave Fourier-Transform Spectrometer) an instrument already demonstrated in the optical and infrared bands. Our device "the millimeterSWIFTS" makes use of Kinetic Inductance Detectors (KID) as light detectors. Multiples aspects of the millimeter SWIFTS development are presented in this report. Design of the key-parts of the device is done with the help of electromagnetic simulations. We also propose a process of fabrication allowing the deposition of an antenna on a silicon nitride membrane SiN. First measurements confirm an adapted behavior of the KID in a SWIFTS design and demonstrate a coupling between the antenna and one of the detectors in themillimeter waves. This opens the way to a future demonstrator. In parallel, the technology developed for the millimeter SWIFTS allowed the deposition of KID on membrane. Main goal here is to assess membranes as a mean to reduce the interaction between cosmic rays and the detector in the case of a space application. Comparative measurements performed on KID deposited on membrane and on substrate demonstrate the same rate of events in both cases. Thus, membrane is not an option for the desired application. However, relaxation time shows a dependency with the presence of substrate.

The observed imbalance of matter and anti-matter in the universe is one of physics' most fundamental unresolved questions. The leading theories to explain this imbalance require CP violation, and the neutron electric dipole moment (nEDM) is a sensitive parameter in its determination. Many new theories of physics beyond the standard model can be constrained or ruled-out by setting limits on the nEDM. Many next generation nEDM experiments require Ultra Cold Neutrons (UCN), produced in superfluid helium. One such experiment is cryoEDM. This thesis explores various types of UCN detection technologies applicable to cryoEDM or any high-density high-efficiency cryogenic nEDM experiment. Cryogenic Phonon Scintillation detectors (CPSD) are modified for this application by operating at 500 mK, and by using a titanium transition edge sensor for phonon signal readout. A CPSD is stabilised in the transition using a novel infra-red light feedback system which reduced the response time to O</m>(100 &mu;s). The detector is characterised and calibrated using an ²⁴¹Am &alpha; source. It was found to operate reliably at this elevated temperature and measure an alpha spectrum with 11% resolution at 5.5 MeV. Scintillators are identified as a promising technology for UCN detection at low temperature. Suitable materials that are bright with fast decay times and low &gamma; sensitivity are studied in the temperature range 300 - 6 K. Their light yield to alpha excitation, their decay time characteristics and spectroscopic properties under VUV excitation are investigated. This study includes the first comprehensive investigation of the luminescence properties of plastic scintillators and of ⁶LiF/ZnS(Ag) down to 6 K. It is found that there is no degradation of the luminescence or kinetic properties of these materials across the whole temperature range, revealing them as suitable cryogenic detector materials. Using a plastic scintillator, a prototype UCN detector for operation in liquid helium is designed, manufactured and tested. It is read out using WLS optical fibres to a room temperature photomultiplier. The detector is successfully tested with cold neutrons at the ISIS neutron science facility and found to effectively measure neutrons, with a signal that is clear from background. Recommendations are made for its integration into a cryogenic neutron EDM experiment. This low-cost detector offers a promising method for the passive detection of UCN in a challenging cryogenic environment, with minimal electric interference and low background sensitivity. This technology offers the potential for improved UCN detection efficiency and thus improved sensitivity of the measurement of the neutron EDM.