Impact of particles on thePlanckHFI detectors: Ground-based measurements and physical interpretation

Abstract

The Planck High Frequency Instrument (HFI) surveyed the sky continuously from August 2009 to January 2012. Its noise and sensitivity performance were excellent (from 11 to 40 aW Hz −1 ), but the rate of cosmic-ray impacts on the HFI detectors was unexpectedly higher than in other instruments. Furthermore, collisions of cosmic rays with the focal plane produced transient signals in the data (glitches) with a wide range of characteristics and a rate of about one glitch per second. A study of cosmic-ray impacts on the HFI detector modules has been undertaken to categorize and characterize the glitches, to correct the HFI time-ordered data, and understand the residual effects on Planck maps and data products. This paper evaluates the physical origins of glitches observed by the HFI detectors. To better understand the glitches observed by HFI in flight, several ground-based experiments were conducted with flight-spare HFI bolometer modules. The experiments were conducted between 2010 and 2013 with HFI test bolometers in different configurations using varying particles and impact energies. The bolometer modules were exposed to 23 MeV protons from the Orsay IPN Tandem accelerator, and to 241 Am and 244 Cm α-particle and 55 Fe radioactive X-ray sources. The calibration data from the HFI ground-based preflight tests were used to further characterize the glitches and compare glitch rates with statistical expectations under laboratory conditions. Test results provide strong evidence that the dominant family of glitches observed in flight are due to cosmic-ray absorption by the silicon die substrate on which the HFI detectors reside. Glitch energy is propagated to the thermistor by ballistic phonons, while thermal diffusion also contributes. The average ratio between the energy absorbed, per glitch, in the silicon die and that absorbed in the bolometer is equal to 650. We discuss the implications of these results for future satellite missions, especially those in the far-infrared to submillimeter and millimeter regions of the electromagnetic spectrum.

Planck2015 results

“…We observe three families of glitches, characterized by their temporal shape. The amplitude and time constants of the decays depend on which part of the satellite is hit (Catalano et al 2014;Planck Collaboration X 2014). These random events are Poisson-distributed in time and produce highly non-Gaussian systematics.…”

Planck2013 results. X. HFI energetic particle effects: characterization, removal, and simulation

“…Indeed, these events have a fast rise time and have a fast decay, and the transfer function built from the short glitch template (see Catalano et al 2014, for a comparison) is in good agreement with the HFI optical transfer function (Planck Collaboration VII 2014), so the energy must be deposited in the environment close to the thermistor. Figure 20 shows the cumulative counts, i.e., the number of events N(>E) with an amplitude higher than a given value E per hour, for short glitches, after converting the maximum amplitude of each glitch to units of energy (keV) for one reference bolometer (100-1b).…”

“…This was first indicated by the ground tests (Catalano et al 2014), showing that the NTD thermometer is sensitive to a temperature change of the Si die. The HFI ground-based calibration data show a rate of events compatible with the cosmic ray flux at sea level over the Si die surface, and the ground-based data also show that almost all these events are in coincidence between PSB-a and PSB-b.…”

“…This analysis is complementary to the study based on ground tests presented in Catalano et al (2014).…”

“…To the left, the quarter-wave backshort can be seen through the aft bolometer absorber mesh. tests using spare HFI bolometers (Catalano et al 2014;Planck Collaboration II 2011), allow identification of the physical cause of the glitch events for two of the types (Sect. 5).…”