Heat source localisation by trilateration of helium II second sound detected with transition edge sensors thermometry

The detection of second sound in He-II can be exploited during superconducting cavity testing to locate the germ of a quench. The sudden appearance of a hotspot generates this wave in the helium II bath, which is routinely detected by Oscillating Superleak Transducers (OST) reacting to the first arrived inter-component velocity front. Recently, we have developed Transition Edge Sensors (TES) that are able to detect second sound by measuring directly the temperature fluctuation of second sound (below milli-Kelvin, in sub-millisecond time scale) with a good native signal-to-noise ratio. We present the current state of development of second sound detectors based on TES, experiments aiming to characterize more thoroughly their behaviour as second sound detectors by thermometry, and the capabilities they provide in terms of localisation of the heat source in the case of direct sight

Towards robust design of thin film transition edge sensors for use in the next-generation superconducting radio frequency cavities

In order to increase the accelerating gradient, the next-generation of Superconducting Radio Frequency (SRF) cavities will be operated with superfluid helium cooling. This upgrade requires the development of a state-of-the-art cryogenic temperature mapping system, which can be used to identify quench initiation in new cavities, and thereby assess their suitability for installation. This paper presents a new mapping system based on an array of Transition Edge Sensors (TESs): electrical devices that exploit the superconducting transition of a thin film to identify temperature changes. The TES array is manufactured using photolithography to deposit a thin film on a 100 mm diameter glass wafer. Two different designs of Au-Sn TES have been assessed; Design 1 was composed of a 10 nm Cr adhesive layer, followed by 20 nm of Au and 100 nm of Sn, and Design 2 was identical except that the Cr layer was not applied. Design 1 showed excellent film adherence, however no superconducting transition was observed. In contrast, Design 2 showed poor film bonding but a superconducting transition. These insights are being used to design a new cryogenic temperature mapping device that combines Design 1 for robust electrical contacts and Design 2 for second sound detection

Fechado de un testigo sedimentario del Lago Rivadavia mediante las técnicas de 210^Pb y 137^Cs

El estudio de cuencas hidrográficas y de los factores que influyen en su formación y características requiere, entre otros trabajos experimentales, la caracterización de testigos sedimentarios de los cauces de los lagos. La secuencia de hechos contenida en ellos se convierte en un registro histórico cuando puede asignarse a las distintas profundidades de la columna una fecha de formación. Las técnicas de fechado de testigos sedimentarios son muy variadas; entre ellas puede nombrarse a las técnicas radimétricas. Éstas se basan en medir la actividad específica de ciertos isótopos presentes –por ejemplo, 210^Pb y 137^Cs– a distintas profundidades y a partir del perfil obtenido, aplicando un modelo matemático conveniente, determinar la edad del estrato como una función de la profundidad. Experimentalmente, la actividad puede determinarse por espectrometría gamma. La técnica basada en 210^Pb requiere la cuantificación del fotopico de 47keV . A tan bajas energías los coeficientes de interacción gamma con la materia son considerables y no pueden ignorarse los efectos de autoatenuación en las muestras medidas. En el presente trabajo se realizó un estudio del fenómeno de autoblindaje en las muestras y atenuación en los componentes estructurales del detector mediante cálculo por método Monte Carlo. Se sistematizó el proceso de estimación de los factores de corrección por autoatenuación. El Laboratorio de Análisis por Activación Neutrónica (LAAN) del Centro Atómico Bariloche (CAB) ha adquirido recientemente un detector de germanio hiperpuro de pozo que por su alta eficiencia es muy adecuado para fechado de sedimentos. Se calibró en eficiencia el detector de pozo para la geometría utilizada en las mediciones del testigo y las energías de interés en fechado por 210^Pb y 137^Cs, teniendo en cuenta las correcciones mencionadas anteriormente. Se estableció un procedimiento claro y ordenado para obtener las actividades específicas corregidas por autoblindaje de las muestras a partir de las áreas de los fotopicos del espectro gamma. Por último, se obtuvo el perfil de actividad específica de 210^Pb, 226^Ra y 137^Cs para un testigo sedimentario del Lago Rivadavia, ubicado en el Parque Nacional Los Alerces, Argentina. El fechado de este sedimento es un paso necesario en la investigación de otros miembros del laboratorio

Fabrication and characterization of NbTi microwave superconducting resonators

Superconducting resonators are widely used in fields spanning from quantum computing to electron spin resonance (ESR) spectroscopy. With the goal of realizing superconducting resonators, a broad variety and combination of superconducting materials, substrates and fabrication processes have been used and thoroughly reported in the literature. High temperature superconductors such as YBCO and low temperature superconductors such as Nb, NbN, NbTiN and Al are the major actors in the domain. In this work, we investigate the possibility to extend the family of suitable low temperature superconductors for the realization of planar superconducting microwave resonators for future ESR applications. In particular, this study focuses on NbTi, a widely used material to realize superconducting cables but not investigated for planar resonating structures at GHz frequencies. A 150 nm thick film of NbTi is sputtered and patterned on top of an Al2O3 substrate. For devices resonating around 6.8 GHz quality factors greater than 10,000 are observed at 3 K and in magnetic fields up to 250 mT

Aluminum nitride on insulator: Material and processing optimization for integrated photonic applications

Thin film aluminum nitride on insulator (AlNOI) has gained attention as a promising material platform for integrated photonic circuits (PICs) due to its ability to operate over a wide spectral range covering the ultra-violet to mid-infrared regions, while enabling a broad range of passive photonic functionalities. This study aims to optimize sputtered AlNOI films for PICs, with an emphasis on the spectroscopic ellipsometry study over a range from 0.19 µm to 25 µm. Furthermore, we discuss our approach for fabricating AlNOI PICs components, with a particular focus on optimizing the etching process to attain smooth sidewall waveguides