Paper detail

Electrostatic Patch Effect in Cylindrical Geometry. II. Forces

We continue our study of patch effect (PE) for two close cylindrical conductors with parallel axes, slightly shifted against each other in the radial and by any length in the axial direction, started in [1], where the potential and energy in the gap were calculated to the second order in the small transverse shift, and to lowest order in the gap to cylinder radius ratio. Based on these results, here we derive and analyze PE force. It consists of three parts: the usual capacitor force due to the uniform potential difference, the one from the interaction between the voltage patches and the uniform voltage difference, and the force due to patch interaction, entirely independent of the uniform voltage. General formulas for these forces are found, and their general properties are described. A convenient model of a localized patch is then suggested that allows us to calculate all the forces in a closed elementary form. Using this, a detailed analysis of the patch interaction for one pair of patches is carried out, and the dependence of forces on the patch parameters (width and strength) and their mutual position is examined. We also give various estimates of the axial patch effect force important for the Satellite Test of the Equivalence Principle (STEP), and recommend intensive pre-flight simulations employing our results.