The Charge Management Research In The Torsion Pendulum

The torsion balance was applied widely in varies of gravitational experiments for itshigh sensitivity on weak force detective. However, the thermal noise of the tungsten fiberused in torsion balance seriously affects its accuracy. Recently quartz fiber has becomemore and more popular in gravitational experiments due to its high Q factor, and manyscientists has took it as an ideal alternative in torsion balance. However the electricallyisolate environment and nonconductivity of quartz would produce an additional chargingnoise. So the charge on the pendulum must be well controlled in order to ensure theaccuracy. In this thesis, we focus on the charge management for the quartz fiber.In first part of this thesis, we review the recently charge management experimentsand analysis their advantages and disadvantages, especially on photoemission effect fromthe incident ultraviolet radiation. In this experiment, the baseline design to mitigate thependulum charge is to shine ultraviolet light on the pendulum and possibly the electrodehousing surfaces.Next, we conduct an experimental apparatus to determine the magnitude of theaccumulation of the electrical charge and the effect of discharging with ultravioletradiation. The results showed that the pendulum can accumulate10-11C charges and have a-6.8V potential in one hour by the ion pump. The charge can be well neutralized and thepotential of pendulum reduced to about-0.2V with discharging by powerful ultravioletlight. This work made a foundation for the next charge management research.