M. Bouzit

PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium

Future cosmology space missions will concentrate on measuring the polarization of the Cosmic Microwave Back- ground, which potentially carries invaluable information about the earliest phases of the evolution of our universe. Such ambitious projects will ultimately be limited by the sensitivity of the instrument and by the accuracy at which polarized foreground emission from our own Galaxy can be subtracted out. We present the PILOT balloon project which will aim at characterizing one of these foreground sources, the polarization of the dust continuum emission in the diffuse interstellar medium. The PILOT experiment will also constitute a test-bed for using multiplexed bolometer arrays for polarization measurements. We present the results of ground tests obtained just before the first flight of the instrument.

Commissioning of a common-user test facility to evaluate the effects of high-energy particles on next-generation cryogenic detectors

Cosmic rays affect the performance of any detector in space through the creation of spurious signal and/or slow build-up of radiation damage. To mitigate the effects of these high-energy particles on the observations of next-generation space missions, the interaction between state-of-the-art detectors will have to be understood through simulation and experimental verification. We present the first measurement results of a new cryogenic system designed to become a common-user test facility to evaluate the effects of high-energy particles on arrays of these high-sensitivity detectors. The system is based on pulse-tube precooled dilution refrigerator with a large experimental volume (ø = 29 cm, H = 30 cm). At 100 mK the system provides 650 µW of cooling power and an out-of-the box thermal stability of 76 µK rms. A first experiment with a semiconducting bolometer from the DIABOLO experiment shows a responsivity and noise level consistent with previous measurement in different cryogenic systems. However, the pulse-tube induced vibrations show as clear features in the noise. To irradiate the detectors a particle beam, such as the 25 MeV proton beam of the nearby ALTO facility, can be coupled to one of four ports. Simulations show that the aluminum-coated Mylar windows do not significantly affect the 25 MeV proton beam of TANDEM. First experiments at the ALTO facility for system verification are expected early 2019. Until that time, the thermal stability, vibration damping and EMI shielding will be improved and a flexible wiring will be developed, to accommodate multiple detector types.

PILOT: optical performance and end-to-end characterisation

PILOT (Polarized Instrument for the Long-wavelength Observations of the Tenuous ISM), is a balloon-borne astronomy experiment dedicated to study the polarization of dust emission from the diffuse ISM in our Galaxy [1]. The observations of PILOT have two major scientific objectives. Firstly, they will allow us to constrain the large-scale geometry of the magnetic field in our Galaxy and to study in details the alignment properties of dust grains with respect to the magnetic field. In this domain, the measurements of PILOT will complement those of the Planck satellite at longer wavelengths. In particular, they will bring information at a better angular resolution, which is critical in crowded regions such as the Galactic plane. They will allow us to better understand how the magnetic field is shaping the ISM material on large scale in molecular clouds, and the role it plays in the gravitational collapse leading to star formation. Secondly, the PILOT observations will allow us to measure for the first time the polarized dust emission towards the most diffuse regions of the sky, where the measurements are the most easily interpreted in terms of the physics of dust. In this particular domain, PILOT will play a role for future CMB missions similar to that played by the Archeops experiment for Planck. The results of PILOT will allow us to gain knowledge about the magnetic properties of dust grains and about the structure of the magnetic field in the diffuse ISM that is necessary to a precise foreground subtraction in future polarized CMB measurements. The PILOT measurements, combined with those of Planck at longer wavelengths, will therefore allow us to further constrain the dust models. The outcome of such studies will likely impact the instrumental and technical choices for the future space missions dedicated to CMB polarization. The PILOT instrument will allow observations in two photometric channels at wavelengths 240 μm and 550 μm, with an angular resolution of a few arcminutes. We will make use of large format bolometer arrays, developed for the PACS instrument on board the Herschel satellite. With 1024 detectors per photometric channel and photometric band optimized for the measurement of dust emission, PILOT is likely to become the most sensitive experiment for this type of measurements. The PILOT experiment will take advantage of the large gain in sensitivity allowed by the use of large format, filled bolometer arrays at frequencies more favorable to the detection of dust emission. This paper presents the optical design, optical characterization and its performance. We begin with a presentation of the instrument and the optical system and then we summarise the main optical tests performed. In section III, we present preliminary end-to-end test results.

Pilot optical alignment

PILOT (Polarized Instrument for Long wavelength Observations of the Tenuous interstellar medium) is a balloonborne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our Galaxy. The PILOT instrument allows observations at wavelengths 240 μm (1.2THz) with an angular resolution about two arc-minutes. The observations performed during the first flight in September 2015 at Timmins, Ontario Canada, have demonstrated the optical performances of the instrument.

Pilot, a balloon borne experiment underground tests

PILOT is a balloon borne experiment, which will measure the polarized emission of dust grains, in the interstellar medium, in the sub millimeter range (with two photometric channels centered at 240 and 550 μm). The primary and secondary mirror must be positioned with accuracies better than 0.6 mm and 0.06°. These tolerances include environmental conditions (mainly gravity and thermo-elastic effects), uncertainties on alignments, and uncertainties on the dilatation coefficient. In order to respect these tolerances, we need precise characterization of each optical component. The characterization of the primary mirror and the integrated instrument is performed using a dedicated submillimeter test bench. A brief description of the scientific objectives and instrumental concept is given in the first part. We present, in the second and in the third part, the status of these ground tests, first results and planned tests.

Optical Design and Ground Tests, for Pilot, a Balloon Borne Experiment for Astronomy

PILOT is a balloon borne experiment, which will measure the polarized emission of interstellar dust grains, in the submillimeter range. We present the instrumental concept and the associated ground tests in progress and planned.