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We developed a cryogenic facility to assess the performance of different types of cryogenic mechanisms. The facility can host very large (up to ∼ 1 m 3 ) and heavy (up to ∼ 30 kg ) instrumentation, cooled down below 10 K. The operation of moving components can be visually monitored by means of two webcams looking inside the 4 K volume. In addition a large number of electrical feedthroughs (444 lines) allow the operation of a set of hall and capacitive sensors to measure both the magnetic field, the position of moving devices with an accuracy of tens of microns and their temperatures with an accuracy of few % . We present the results of the first tests on a large aperture (500 mm diameter) superconducting magnetic bearing for the SWIPE/LSPE experiment currently under test.

Kinetic Inductance Detectors (KIDs) are superconductive low-temperature detectors useful for astrophysics and particle physics. We have developed arrays of lumped elements KIDs (LEKIDs) sensitive to microwave photons, optimized for the four horn-coupled focal planes of the OLIMPO balloon-borne telescope, working in the spectral bands centered at 150 GHz, 250 GHz, 350 GHz, and 460 GHz. This is aimed at measuring the spectrum of the Sunyaev-Zel'dovich effect for a number of galaxy clusters, and will validate LEKIDs technology in a space-like environment. Our detectors are optimized for an intermediate background level, due to the presence of residual atmosphere and room-temperature optical system and they operate at a temperature of 0.3 K. The LEKID planar superconducting circuits are designed to resonate between 100 and 600 MHz, and to match the impedance of the feeding waveguides; the measured quality factors of the resonators are in the 104 - 105 range, and they have been tuned to obtain the needed dynamic range. The readout electronics is composed of a cold part, which includes a low noise amplifier, a dc-block, coaxial cables, and power attenuators; and a room-temperature part, FPGA-based, including up and down-conversion microwave components (IQ modulator, IQ demodulator, amplifiers, bias tees, attenuators). In this contribution, we describe the optimization, fabrication, characterization and validation of the OLIMPO detector system.

The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs, MISTRAL, is a cryogenic LEKID camera, operating in the W band ( 77 - 103 GHz ) from the Gregorian focus of the 64-m aperture Sardinia Radio Telescope (SRT), in Italy. This instrument features a high angular resolution ( ∼ 12 arcsec ) and a wide instantaneous field of view ( ∼ 4 arcmin ), allowing continuum surveys of the mm-wave sky with many scientific targets, including observations of galaxy clusters via the Sunyaev–Zel’dovich effect. In May 2023, MISTRAL has been installed at SRT for the technical commissioning. In this contribution, we will describe the MISTRAL instrument focusing on the laboratory characterization of its focal plane: a ∼ 400 -pixel LEKID array. We will show the optical performance of the detectors highlighting the procedure for the identification of the pixels on the focal plane, the measurements of the optical responsivity and NEP, and the estimation of the optical efficiency.

OLIMPO is a balloon-borne experiment aiming at spectroscopic measurements of the Sunyaev-Zel'dovich effect in clusters of galaxies. The instrument operates from the stratosphere, so that it can cover a wide frequency range (from ∼ 130 to ∼ 520 GHz in 4 bands), including frequencies which are not observable with ground-based instruments. OLIMPO is composed of a 2.6-m aperture telescope, a differential Fourier transform spectrometer and four arrays of lumped element kinetic inductance detectors operating at the temperature of 0.3 K. The payload was launched from the Longyearbyen airport (Svalbard Islands) on July 14th, 2018, and operated for 5 days, at an altitude of 38 km around the North Pole. We report the in-flight performance of the first lumped element kinetic inductance detector arrays ever flown onboard a stratospheric balloon.

OLIMPO is a proposed Antarctic balloon-borne Sunyaev-Zel’dovich effect (SZE) imager to study gas dynamics associated with structure formation along with the properties of the warm-hot intergalactic medium (WHIM) residing in the connective filaments. During a 25 day flight OLIMPO will image a total of 10 z ∼0.05 galaxy clusters and 8 bridges at 145, 250, 365, and 460 GHz at an angular resolution of 1.0′–3.3′. The maps will be significantly deeper than those planned from CMB-S4 and CCAT-P, and will have excellent fidelity to the large angular scales of our low- z targets, which are difficult to probe from the ground. In combination with X-ray data from eROSITA and XRISM we will transform our current static view of galaxy clusters into a full dynamic picture by measuring the internal intra-cluster medium (ICM) velocity structure with the kinematic SZE, X-ray spectroscopy, and the power spectrum of ICM fluctuations. Radio observations from ASKAP and MeerKAT will be used to better understand the connection between ICM turbulence and shocks with the relativistic plasma. Beyond the cluster boundary, we will combine thermal SZE maps from OLIMPO with X-ray imaging from eROSITA to measure the thermodynamics of the WHIM residing in filaments, providing a better understanding of its properties and its contribution to the total baryon budget.

We describe the setup for the broadband millimeter/submillimeter characterization of the quasi-optical elements and the dielectric materials commonly used in microwave receivers operated in microwave astronomy. The setup is made of a large aperture (100 mm) Fourier transform spectrometer coupled to a transition edge superconducting detector. The system has been assembled and characterized in different configurations and operation modes for the acquisition of interferograms from various kinds of samples. After the initial test runs, the configuration is now being updated to ensure a broader range of measurements, including reflectance and scattering. We plan to first use this testbed for the characterization of the dielectric materials used in the LSPE/SWIPE experiment, devoted to the study the polarization of the Cosmic Microwave Background.

Large radio and mm–wave telescopes use very sensitive detectors requiring cryogenic cooling to reduce detector noise. Pulse Tubes (PT) cryocoolers are widely used to reach temperatures of a few K, defining the base temperature of further sub–K stages. This technology represents an effective solution for continuous operation, featuring high stability and reduced vibration levels on the detectors. However, the compressor used to operate the PT is a significant source of microphonics and electrical noise, making its use at the focus of large steerable telescopes not advisable. This calls for long flexible helium lines between the compressor, operated at the base of the radio telescope, and the cold–head, mounted in the receivers cabin with the receiver detectors. The distance between the receiver cabin and the base can be >100 m long for large radio telescopes. In the framework of our development of the MIllimetric Sardinia radio Telescope Receiver based on Array of Lumped elements kids (MISTRAL), a W–band camera working at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope (SRT) with an array of Lumped Elements Kinetic Inductance Detectors (LEKID), we have developed a cryogenic system based on a PT refrigerator as the first cooling stage. Here we describe the MISTRAL cryogenic system and focus on the validation of the use of a commercial PT Cryocooler with 100 m helium lines running from the cold head to the compressor unit. The configuration allows us to operate the 0.9 W PT reaching below 4.2 K with 0.5 W dissipation.

The MIllimetric Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs, MISTRAL, is a cryogenic W-band (77–103 GH) LEKID camera which will be integrated at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope, in Italy, in Autumn 2022. This instrument, thanks to its high angular resolution ( ∼ 13 arcsec ) and the wide instantaneous field of view ( ∼ 4 arcmin ), will allow continuum surveys of the mm-wave sky with a variety of scientific targets, spanning from extragalactic astrophysics to solar system science. In this contribution, we will describe the design of the MISTRAL camera, with a particular focus on the optimisation and test of a prototype of the focal plane.

We describe the in-flight performance of the horn-coupled lumped element kinetic inductance detector arrays of the balloon-borne OLIMPO experiment. These arrays have been designed to match the spectral bands of OLIMPO: 150, 250, 350, and 460 GHz , and they have been operated at 0.3 K and at an altitude of 37.8 km during the stratospheric flight of the OLIMPO payload, in Summer 2018. During the first hours of flight, we tuned the detectors and verified their large dynamics under the radiative background variations due to elevation increase of the telescope and to the insertion of the plug-in room-temperature differential Fourier transform spectrometer into the optical chain. We have found that the detector noise equivalent powers are close to be photon noise limited and lower than those measured on the ground. Moreover, the data contamination due to primary cosmic rays hitting the arrays is less than 3% for all the pixels of all the arrays and less than 1% for most of the pixels. These results can be considered the first step of KID technology validation in a representative space environment.

In this paper, we present beam pattern tests performed on the SWIPE multi-mode bolometric detector pixel assembly. A 20-mm-aperture horn is coupled to a large detector absorber (10 mm diameter) with a TES sensor located on the side. The pixel assembly has been tested at the bolometer base temperature of 340 mK, inside a custom cryogenic test bed, looking at a Gunn oscillator (128 GHz) located in the far field. We developed a custom cryogenic neoprene absorber, in addition to the stack of standard metal meshes low-pass filters, to reduce the background on the detector at a level similar to the one expected in flight, allowing to measure the main beam of the pixel assembly. The measured FWHM is 21 ∘ , slightly narrower than the expected one (24 ∘ ), due to vignetting produced by the filters stack.