Predicting the response of a submillimeter bolometer to cosmic rays

Bolometers designed to detect. submillimeter radiation also respond to cosmic, gamma, and x rays. Because detectors cannot be fully shielded from such energy sources, it is necessary to understand the effect of a photon or cosmic-ray particle being absorbed. The resulting signal (known as a glitch) can then be removed from raw data. We present measurements using an Americium-241 gamma radiation source to irradiate a prototype bolometer for the High Frequency Instrument in the Planck Surveyor satellite. Our measurements showed no variation in response depending on where the radiation was absorbed, demonstrating that the bolometer absorber and thermistor thermalize quickly. The bolometer has previously been fully characterized both electrically and optically. We find that using optically measured time constants underestimates the time taken for the detector to recover from a radiation absorption event. However, a full thermal model for the bolometer, with parameters taken from electrical and optical measurements, provides accurate time constants. Slight deviations from the model were seen at high energies; these can be accounted for by use of an extended model

First Tests of Prototype SCUBA-2 Superconducting Bolometer Array

We present results of the first tests on a 1280 pixel superconducting bolometer array, a prototype for SCUBA‐2, a sub‐mm camera being built for the James Clerk Maxwell Telescope in Hawaii. The bolometers are TES (transition edge sensor) detectors; these take advantage of the large variation of resistance with temperature through the superconducting transition. To keep the number of wires reasonable, a multiplexed read‐out is used. Each pixel is read out through an individual DC SQUID; room temperature electronics switch between rows in the array by biasing the appropriate SQUIDs in turn. Arrays of 100 SQUIDs in series for each column then amplify the output. Unlike previous TES arrays, the multiplexing elements are located beneath each pixel, making large arrays possible, but construction more challenging. The detectors are constructed from Mo/Cu bi‐layers; this technique enables the transition temperature to be tuned using the proximity effect by choosing the thickness of the normal and superconducting materials. To achieve the required performance, the detectors are operated at a temperature of approximately 120 mK. We describe the results of a basic characterisation of the array, demonstrating that it is fully operational, and give the results of signal to noise measurements

Receiver development for BICEP Array, a next-generation CMB polarimeter at the South Pole

A detection of curl-type (B-mode) polarization of the primary CMB would be direct evidence for the inflationary paradigm of the origin of the Universe. The Bicep/Keck Array (BK) program targets the degree angular scales, where the power from primordial B-mode polarization is expected to peak, with ever-increasing sensitivity and has published the most stringent constraints on inflation to date. Bicep Array (BA) is the Stage-3 instrument of the BK program and will comprise four Bicep3-class receivers observing at 30/40, 95, 150 and 220/270 GHz with a combined 32,000+ detectors; such wide frequency coverage is necessary for control of the Galactic foregrounds, which also produce degree-scale B-mode signal. The 30/40 GHz receiver is designed to constrain the synchrotron foreground and has begun observing at the South Pole in early 2020. By the end of a 3-year observing campaign, the full Bicep Array instrument is projected to reach σr between 0.002 and 0.004, depending on foreground complexity and degree of removal of B-modes due to gravitational lensing (delensing). This paper presents an overview of the design, measured on-sky performance and calibration of the first BA receiver. We also give a preview of the added complexity in the time-domain multiplexed readout of the 7,776-detector 150 GHz receiver

Optimisation of performance of dispersants in aqueous titanium slips

Slip casting is a well-established ceramic casting technique used for large scale fabrication of ceramic products with complex shapes. A homogenous slip with a desired level of stability is required, which is controlled using a dispersant. This paper describes the selection and optimisation of various dispersants used to produce Ti powder slips. A consideration of the effect of concentration and pH of the solvent on the dispersion of anionic polyelectrolyte dispersants (Dispex N-40, Synthecol SD375 & Dolapix CE64) was examined by measuring the sedimentation height and rate, the streaming potential and the slip viscosity. It was found that Dolapix CE64 showed the best deflocculating effect at 0.3dw.% with pH of 7. In particular, the measurements on Dolapix CE64 gave consistent results. This indicated that Dolapix CE64 is an effective dispersant in the preparation of a titanium slip

Broadband coated lens solutions for FIR-mm-wave instruments

This paper presents recent results of ongoing European Space Agency funded program of work aimed at developing large dielectric lenses suitable for future satellite missions, with a particular focus on requirements for CMB polarimetry. Two lens solutions are being investigated: (i) polymer lenses with broadband multi-layer antireflection coatings; (ii) silicon lenses with surface-structured anti-reflection coating represented by directly machined pyramidal features. For each solution, base materials with and without coatings have been optically characterized over a range of temperatures down to ~10 K. Full lens solutions are under manufacture and will be tested in a bespoke large cryo-optical facility...

Fabrication of prototype imaging arrays for SCUBA-2

Prototype imaging subarrays for SCUBA-2 (the Submillimeter Common-User Bolometer Array) have been fabricated and tested. The pixel count (1280) of these wafer-scale imagers is significantly larger than any other low-temperature detectors produced to date, and represents a major step forward for the low-temperature detector community. These transition-edge-sensor (TES) based imagers utilize several innovations including in-focal-plane superconducting quantum intereference device (SQUID) multiplexers, micromachined Si block absorbers, and superconducting wafer hybridization. In this paper, we review the fabrication processes developed for these imagers and present recent optical data from a prototype imaging subarray

The Mexico UK Sub-mm Camera for Astronomy (MUSCAT) on-sky commissioning: performance of the cryogenic systems

MUSCAT is a new 1.1 mm band receiver which was installed on the 50 m Large Millimeter Telescope atop Volc´an Sierra Negra in Puebla, Mexico during the final quarter of 2021 and commissioned on sky throughout 2022. MUSCAT uses a novel cooling chain consisting of a commercial pulse tube cooler, two thermal stages of passively-switched continuous sorption coolers, and a final miniature dilution refrigerator. Through this system MUSCAT achieves a continuous temperature of 120 mK at the focal plane and has shown continuous operation at this temperature for greater than 100 days during readiness testing. Through minimising the amount of helium-3 required, the design on MUSCAT’s cryogenic systems produced a reliable, cost-effective cooling platform. Here we present the cryogenic design and performance of MUSCAT on-sky and compare this to that achieved during deployment-readiness testing at Cardiff (UK). We consider both cooldown time and achieved base temperature. We look at the impact on operation of relocating a pulse-tube cooled instrument from a development lab running on a 50 Hz mains electricity supply to a site running at 60 Hz. Finally, we describe the process of preparing the MUSCAT instrument for shipping and assess the success of this process in terms of remedial work required upon arrival