Expected Electric Charging Rates and Measuring the Charge On the Inner Sphere In the Two-Sphere EP Experiment

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Electric Charging of a Drag-Free Proof Mass

Electric charge on a Drag-Free satellite proof mass is one of the largest disturbances to pure drag-free motion or an accurate Equivalence-Principle (EP) experiment. Electric charge can be managed, however, and when it is kept sufficiently small, the largest disturbance for an EP experiment is Brownian motion due to the residual vacuum.

The high-accuracy EP experiment uses two proof masses, a sphere inside of a spherical shell. The question has arisen whether or not the charge on the inner sphere completely surrounded by the shell could be measured. At the 9th Marcel Grossmann Meeting in Rome in 2000, a paper was presented which examined the expected charging rate on a Drag-Free satellite proof mass and which presented a method for measuring the charge on the inner sphere.

The MG9 paper, Expected Electric Charging Rates and Disturbances In a Two-Sphere Free-Fall Equivalence-Principle Experiment in a Drag-Free Satellite (PDF), may be downloaded from this website.