COHERENT FOURIER COMPONENTS IN THE LISA MEASUREMENT BANDWIDTH FROM TEST MASS CHARGING: ESTIMATES AND SUPPRESSION

Abstract

The success of LISA is dependent on the precision with which the test masses, the interferometer mirrors, can maintain pure geodesic motion. Their accumulation of charge from cosmic rays and solar wind particles can give rise to spurious Lorentz and Coulomb forces. Coherent Fourier components, which appear due to the time dependence of the amount of charge accrued, are estimated to exceed the acceleration noise target. The general forms of these signals are derived. It is shown that for typical parameter values, coherent signals with significant signal-to-noise ratios can result from Coulomb interactions, while the signal from Lorentz interactions is expected to fall below the instrumental noise target. In this description, the signals' peak magnitudes are shown to increase with decreasing frequency. Hence their impact may be greater for missions that aim to look for gravitational waves at frequencies below the nominal LISA band. It is expected that the accuracy with which these signals can be removed from the data will depend on deviations from the predictable temporal behavior of the parameters on which they are dependent. Methods to substantially decrease these signals for LISA are discussed.