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Study of Cosmic Ray Impact on Planck/HFI Low Temperature Detectors

Abstract : The Planck High Frequency Instrument (HFI) has been surveying the sky continuously from the second Lagrangian point (L2) between August 2009 and January 2012. It operates with 52 high impedance bolometers cooled at 100 mKaaOnce that the focal plane of the HFI instrument of the Planck mission (launched in May 2009) has reached operational temperature, we have observed the thermal effect of cosmic ray interactionwith the Planck satellite, located at Lagrangian point L2.When a particle hits a component of the bolometers (e.g.: thermometer, grid or wafer) composing the focal plane of HFI, a thermal spike (called glitch), due to deposited energy, is observed. Processing these data revealed another effect due to high energy cosmic ray particle showers: High Coincidence Events (HCE), composed of glitches occurring coincidentally in many detectors and with a temperature increase from nK to μKafter the shower.Aflux of about 100 HCE per hour has been calculated. Two types of HCE have been detected: fast and slow. For the first type, the untouched bolometers reach the same temperature as the touched ones in a few seconds which can be explained by a storage of the deposited energy in the stainless steel focal plane. The second type of HCE is not fully understood yet. These effects might be explained by extra conduction from the helium released from cryogenic surfaces, creating a temporary thermal link between the different stages of the HFI. in a range of frequency between 100 GHz and 1 THz with unprecedented sensitivity, but strong coupling with cosmic radiation. At L2, the particle flux is about 5 hbox {cm}^{-2} hbox {s}^{-1} and is dominated by protons incident on the spacecraft. Protons with an energy above 40 MeV can penetrate the focal plane unit box causing two different effects: glitches in the raw data from direct interaction of cosmic rays with detectors (producing a data loss of about 15 % at the end of the mission) and thermal drifts in the bolometer plate at 100 mK adding non-Gaussian noise at frequencies below 0.1 Hz. The HFI consortium has made strong efforts in order to correct for this effect on the time ordered data and final Planck maps. This work intends to give a view of the physical explanation of the glitches observed in the HFI instrument in-flight. To reach this goal, we performed several ground-based experiments using protons and α particles to test the impact of particles on the HFI spare bolometers with a better control of the environmental conditions with respect to the in-flight data. We have shown that the dominant part of glitches observed in the data comes from the impact of cosmic rays in the silicon die frame supporting the micro-machined bolometric detectors propagating energy mainly by ballistic phonons and by thermal diffusion. The implications of these results for future satellite missions will be discussed.
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Submitted on : Wednesday, September 10, 2014 - 8:38:18 AM
Last modification on : Wednesday, September 23, 2020 - 4:36:13 AM

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A. Miniussi, J.-L. Puget, W. Holmes, G. Patanchon, A. Catalano, et al.. Study of Cosmic Ray Impact on Planck/HFI Low Temperature Detectors. 15th International Workshop on Low Temperature Detectors (LTD15), Jun 2013, Pasadena, United States. 176, pp.815-821, 2014, ⟨10.1007/s10909-014-1104-x⟩. ⟨in2p3-01062532⟩

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