Control of surface charge on insulating hollow cylinder by using shield-ring in vacuum

In vacuum, insulators acquire charge due to well-known Secondary Electron Emission Avalanche (SEEA), and the charge is considered harmful for the insulation of high voltage vacuum devices. This paper deals with the charge depression effect of a shieldring, a ring type electrode, which is often applied to high voltage devices in order to relax the electric field near the triple junction on a cathode. In the present study a shield-ring is located in an insulating hollow cylinder made of Al2O3. The charge distribution on the inner surface is measured by employing an electrostatic probe located outside of the cylinder. The probe has scanned the whole surface of the cylinder and produced a probe output pattern that varies in shape depending on the ring height. On the other hand, we have calculated the charge distribution on the inner surface of the cylinder by employing a rotationally symmetric i.e. two dimensional simulation method relying on the SEEA mechanism. Giving the calculated distribution, we have further calculated the probe output by using a three dimensional simulation method. The calculated and measured probe output patterns show a reasonable agreement for several ring heights tested in this study. Based on these experimental and analytical results, we have revealed the effectiveness of using a shield-ring to depress the SEEA charging.