Discharging Fused Silica Optics Occluded by an Electrostatic Drive

Charge accumulation on test masses is a potentially limiting noise source for gravitational-wave interferometers, and may occur due to exposure to an electrostatic drive (ESD) in modern test mass suspensions. In this talk I will show that an ESD can cause charge accumulation on a fused silica test mass at a rate of 8 * 10$^{\mathrm{-16}}$ C/cm$^{\mathrm{2}}$/hr. I will also describe a charge mitigation system consisting of a stream of nitrogen ionized by copper feedthrough pins at 3750 VAC. This system can neutralize positive and negative charge from 10$^{\mathrm{-11}}$ C/cm$^{\mathrm{2}}$ to 3 * 10$^{\mathrm{-14}}$ C/cm$^{\mathrm{2}}$ in under two hours.