LISA Pathfinder test-mass charging during galactic cosmic-ray flux short-term variations

Abstract

Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder (LPF), meant for subsystems diagnostics, was devoted to the measurement of galactic cosmic-ray and solar energetic particle integral fluxes above 70 MeV n −1 up to 6500 counts s −1. PD data were gathered with a sampling time of 15 s. Characteristics and energy-dependence of GCR flux recurrent depressions and of a Forbush decrease dated August 2, 2016 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections (ICMEs) is also discussed.

Characteristics and Energy Dependence of Recurrent Galactic Cosmic-Ray Flux Depressions and of a Forbush Decrease with LISA Pathfinder

“…The energy dependence of 27-day GCR flux variations, for instance, is discussed in Grimani et al (2015) and references therein. The shielding effect of the atmosphere and the geomagnetic cut-off prevent neutron monitors to carry out a direct measurement of cosmic-ray energy spectra below effective energies of several GeV, although they can be obtained by using models combined with neutron monitors observations (Beer 2000;Hofer & Flückiger 2000;Usoskin et al 2011Usoskin et al , 2017.…”

“…Measurements of the energy dependence of GCR flux recurrent and non-recurrent depressions and the study of their evolution can be used to estimate the test-mass charging aboard future generation LISA-like interferometers (Grimani et al 2015, and references therein). Despite minor changes in the instrument performance due to GCR short-term variations, future interferometers devoted to gravitational wave detection in space will detect sub-femto-g spurious acceleration at low frequencies (∼10 −5 Hz), and the role of any interplanetary disturbance must be evaluated and quantified.…”

Electron test-mass charging aboard the future space interferometers

“…The role of cosmic rays in affecting the performance of gravitational-wave detectors was also considered for ground-based devices (see Ref. 9 and references therein). The minimum energy of protons and ions penetrating and charging the LISA-PF test masses is 100 MeV/n.…”

“…9. A simplified shell matter distribution of the spacecraft around the test-mass was considered in Refs.…”

“…Details on the LISA-PF geometry is reported in Ref. 9 The net charging rate in the test masses is defined as it follows:…”