Achievement of extreme high vacuum in the order of 10−10 Pa without baking of test chamber

Abstract

Reduction of roughness of a vacuum surface is one of the most important points to reduce outgassing from the surface. Electrochemical buffing has been applied to a test chamber made of stainless steel for this aim. Analysis of the treated surface results in a roughness of 0.1 μm Rmax, a homogeneous topography, a Cr enrichment of 80% compared with untreated surface and a formation of Cr2O3 at the surface. The chamber was pumped by a titanium sublimation pump and two turbo molecular pumps with magnetic bearings in series. Pressure in the chamber was measured by two extractor gauges. A pressure of 3×10−7 Pa was obtained at the fourth day after it started pumping, and subsequently only the turbo molecular pumps and the titanium sublimation pump were baked at 120°–350° for 72 h. The pressure of the chamber finally reached 8×10−10 Pa with liquid nitrogen cooling at the 15th day. A pressure of 3×10−9 Pa could be maintained without any activation and any liquid nitrogen cooling of the titanium sublimation pump.