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    Vacuum Science & Technology Wednesday Sessions
       Session VST-WeM

Paper VST-WeM8
Outgassing Measurements of Stacked Laminations for Use as an Electromagnet Core

Wednesday, October 31, 2001, 10:40 am, Room 125

Session: Gas Sorption Phenomena I
Presenter: Y. Saito, KEK-High Energy Accelerator Research Organization, Japan
Authors: Y. Saito, KEK-High Energy Accelerator Research Organization, Japan
Y. Sato, KEK-High Energy Accelerator Research Organization, Japan
T. Kubo, KEK-High Energy Accelerator Research Organization, Japan
Correspondent: Click to Email
Electromagnets, involving ferrite or lamination cores, are often installed in a vacuum of accelerator system so as to bend and extract the beam. Outgassing from the cores is one of the problems, since it causes a poor vacuum, thus shortening a beam lifetime and also inducing an electrical breakdown. Outgassing measurements by a throughput method were carried out for laminations with a few kinds of insulating coatings; a quasi-inorganic and inorganic materials. It is to be noticed that the outgassing rates for loosely- and closely-stacked lamination cores do not show any significant difference for each coating, when the pumping period is as long as 100 hours, or more. Further, though pre-baking of the laminations is effective to shorten the pumping period, once exposed to atmospheric air with humidity, the outgassing rate again shows a larger value. Probably, the adsorbed/absorbed water molecules on/in the coatings require an activation energy to desorb, while, once desorbing, they can diffuse more easily, even in a narrow gap of several microns or less. This indicates that the pump-down characteristic is dominated by the coating materials, rather than by a gap distance between laminations. Indeed, stainless-steel laminations without any coatings showed much lower outgassing rates, even when closely stacked. Further, a time lag in the pump-down characteristic of the closely stacked laminations (a 100 mm-square sheet) is estimated to be several hours by a Monte-Carlo simulation, being shorter than 100 hours of pumping.