AVS 53rd International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP13
Outgassing Rates of Stainless Steel Pipes Treated with 400°C Air Bake

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Vacuum Technology Poster Session
Presenter: X. Liu, Cornell University
Authors: X. Liu, Cornell University
K.W. Smolenski, Cornell University
Y. Li, Cornell University
C.K. Sinclair, Cornell University
Correspondent: Click to Email
Creating an extreme-high vacuum environment is essential to the operational lifetime of the photo-cathode in the high voltage DC electron gun of the Cornell Energy Recovery Linac project. The key is to achieve an ultra-low hydrogen outgassing rate (OR) of the chamber material. Studies have reported dramatic decreases in hydrogen OR for stainless steels (SST) after a 400°C air bake. In this paper, we report the results of 400°C air bakeout of 304L SST tubes. The tested SST tubes are 6" in diameter and 40" long, with 8" ConFlat flanges welded to both ends. The tubes were cut from long tubes of the same production lot to assure consistent material properties and history. All bakeouts were carried out in a specially built oven to provide uniform temperature. The SST ORs were measured by two methods. A spinning rotor gauge was used for a rate-of-rise method by valving out the tube from active pumps and gauges. For a throughput measurement, the tube was connected to a measurement chamber (MC) through a small orifice. The MC is pumped by an ion pump through a second orifice, to give a known pumping speed, and is equipped with a cold cathode ion gauge and a residual gas analyzer. The two methods agree very well. For each sample SST tube, ORs were measured after 150°C and 250°C vacuum bakeout both before and after a 400°C air bake. We have observed as much as a factor of three of reduction in the SST ORs, with a lowest measured OR of 3x10@super -13@ Torr l s@super -1@ cm@super -2@. This reduction in SST OR is significant, though much smaller than other reported values. Evidence also shows that bakeout history has a strong effect; higher bakeout temperature may result in higher outgassing rate.