Unwanted, coherent signals in the LISA bandwidth due to test mass charging

Electrical charges will build up on the LISA test masses due to particle radiation from cosmic rays and from the Sun. This charging can lead to spurious forces both through Lorentz and Coulomb interactions. These effects can give rise not only to acceleration noise, but also to unwanted coherent signals in the LISA bandwidth, due to the time dependence of the amount of charge accumulated on a test mass. The amplitude of these unwanted coherent signals depends on several factors, including the charging rate, the maximum allowed charge, the discharge procedure and a number of design parameters of the sensor itself. This paper estimates the magnitude of such unwanted charging signals based on the current, nominal LTP sensor dimensions and discusses approaches that may be taken to substantially reduce them for LISA