Showing papers by "F. Couchot published in 2020"

Planck 2018 results: III. High frequency instrument data processing and frequency maps

Abstract: This paper presents the High Frequency Instrument (HFI) data processing procedures for the Planck 2018 release. Major improvements in mapmaking have been achieved since the previous Planck 2015 release, many of which were used and described already in an intermediate paper dedicated to the Planck polarized data at low multipoles. These improvements enabled the first significant measurement of the reionization optical depth parameter using Planck -HFI data. This paper presents an extensive analysis of systematic effects, including the use of end-to-end simulations to facilitate their removal and characterize the residuals. The polarized data, which presented a number of known problems in the 2015 Planck release, are very significantly improved, especially the leakage from intensity to polarization. Calibration, based on the cosmic microwave background (CMB) dipole, is now extremely accurate and in the frequency range 100–353 GHz reduces intensity-to-polarization leakage caused by calibration mismatch. The Solar dipole direction has been determined in the three lowest HFI frequency channels to within one arc minute, and its amplitude has an absolute uncertainty smaller than 0.35 μ K, an accuracy of order 10−4 . This is a major legacy from the Planck HFI for future CMB experiments. The removal of bandpass leakage has been improved for the main high-frequency foregrounds by extracting the bandpass-mismatch coefficients for each detector as part of the mapmaking process; these values in turn improve the intensity maps. This is a major change in the philosophy of “frequency maps”, which are now computed from single detector data, all adjusted to the same average bandpass response for the main foregrounds. End-to-end simulations have been shown to reproduce very well the relative gain calibration of detectors, as well as drifts within a frequency induced by the residuals of the main systematic effect (analogue-to-digital convertor non-linearity residuals). Using these simulations, we have been able to measure and correct the small frequency calibration bias induced by this systematic effect at the 10−4 level. There is no detectable sign of a residual calibration bias between the first and second acoustic peaks in the CMB channels, at the 10−3 level.

Benefits of Bolometer Joule Stepping and Joule Pulsing

Abstract: We introduce the ‘Joule stepping’ technique, whereupon a constantly biased bolometer has its bias voltage modified by a small additional step. We demonstrate this technique using a composite NTD semiconductor bolometer and a pulsing device that sends an extra step in voltage. We demonstrate the results of the technique over a range of bias voltages at 100, 200 and 300 mK. Joule stepping allows us to directly measure long thermal tails with low amplitudes in the response of the global thermal architecture of bolometers and could be a useful tool to quickly and easily calibrate the thermal time response of individual bolometric detectors or channels. We also show that the derivative of the Joule step is equivalent to the bolometer response to a $$\delta $$-pulse (or Joule pulse), which allows for greater understanding of transient behaviour with a better signal-to-noise ratio than pulsing alone can provide. Finally, we compare Joule step pulses with pulses produced by $$\alpha $$ particles, finding a good agreement between their fast decay constants, but a discrepancy between their thermal decay constants.

Simulations of athermal phonon propagation in a cryogenic semiconducting bolometer

Abstract: We present three Monte Carlo models for the propagation of athermal phonons in the diamond absorber of a composite semiconducting bolometer ‘Bolo 184'. Previous measurements of the response of this bolometer to impacts by α particles show a strong dependence on the location of particle incidence, and the shape of the response function is determined by the propagation and thermalisation of athermal phonons. The specific mechanisms of athermal phonon propagation at this time were undetermined, and hence we have developed three models for probing this behaviour by attempting to reproduce the statistical features seen in the experimental data. The first two models assume a phonon thermalisation length determined by a mean free path λ, where the first model assumes that phonons thermalise at the borders of the disc (with a small λ) and the second assumes that they reflect (with a λ larger than the size of the disc). The third model allows athermal photons to propagate along their geometrical line of sight (similar to ray optics), gradually losing energy. We find that both the reflective model and the geometrical model reproduce the features seen in experimental data, whilst the model assuming phonon thermalisation at the disc border produces unrealistic results. There is no significant dependence on directionality of energy absorption in the geometrical model, and in the schema of this thin crystalline diamond, a reflective absorber law and a geometrical law both produce consistent results.