Attainment of Outgassing Rates Below 10-13 Torr Liters/Sec Cm2 for Aluminium and Stainless Steel After Bakeout at Moderate Temperatures

Abstract

Outgassing rates after bakeout were measured for stainless steel and aluminium by means of the throughput-method. Sample preparation before experiments: workshop machining, rinsing in acetone, 20 h vacuum bakeout at 150°C (to remove initial contaminations). Prior to each experiment the samples were filled with air (>96 percent relative humidity). After a 20 h vacuum bakeout at 100°C the outgassing rates are 4×10-14 Torr liters/sec cm2 for aluminium (mainly CO) and 1×10-12 Torr liters/sec cm2 for stainless steel (mainly H2). After an air bakeout at 100°C (i.e. bakeout in air at atmospheric pressure for 2 h followed by a vacuum bakeout for 18 h) outgassing rates of 2.8×10-14 Torr liters/sec cm2 (A1) and 1×10-13 Torr liters/sec cm2 (s.s.) are obtained. For stainless steel an air bakeout at 400°C followed by a 18 h vacuum bakeout gives outgassing rates in the low 10-14 Torr liters/sec cm2 range. These low outgassing rates of stainless steel are not affected by subsequent chemical etching or by mechanical polishing: outgassing rates of below 2×10-13 Torr liters/sec cm2 can be achieved routinely from such samples after a 20 h vacuum bakeout at 100°C.