DEVELOPMENT OF METHODS TO SUBSTANTIALLY REDUCE PHOTODESORPTION FROM STORAGE RING PHOTO ABSORBERS

DESIGN FOR STORAGE RINGS SUCH AS THE ADVANCED PHOTON SOURCE, THE ADVANCED LIGHT SOURCE, AND THE PROPOSED B FACTORY REQUIRE THE DEVELOPMENT OF INNOVATIVE PHOTON ABSORBERS THAT CAN, IN MOST CASES, ABSORB SUBSTANTIALLY MORE POWER THAN IS CURRENTLY ACHIEVED BY ABSORBERS IN CONVENTIONAL STORAGE RINGS. THE FABRICATION MATERIAL CHOSEN MUST MEET THERMAL AND STRESS REQUIREMENTS. AS A RESULT, COPPER MATERIALS ARE USUALLY SPECIFIED, AND THE MATERIAL PHOTODESORPTION YIELD IS MEASURED WITH AND WITHOUT COATINGS. THE VACUUM IS ADVERSELY AFFECTED BY THE PHOTODESORPTION PRODUCTS, AND THE MATERIAL THAT EXHIBITS THE SMALLEST PHOTOYIELD CROSS SECTION IS SOUGHT. CURRENTLY, LITTLE OR NO UNDERSTANDING EXISTS OF THE DESORPTION MECHANISM OR OF THE SURFACE CHEMISTRY THAT PRODUCES THE PHOTOYIELD. THE DESORPTION OF MOLECULES FROM VACUUM SYSTEM WALLS OR ABSORBERS IS SIMPLY DESCRIBED AS RESULTING FROM PHOTOELECTRONS THAT ARE PRODUCED BY THE IMPINGING RADIATION. HOWEVER, MOST OF THE DESORPTION PROBABLY OCCURS VIA A SURFACE RECOMBINATION REACTION. THE LACK OF COMPREHENSIVE KNOWLEDGE OF THE DESORPTION MECHANISM FOSTERS SELECTION OF MATERIAL OR COATINGS BY INTUITION. THE PHASE I STUDY IS DETERMINING THE COMPLETE DESORPTION MECHANISM AND DEVELOPING METHODS TO SUBSTANTIALLY REDUCE OR ELIMINATE PHOTODESORPTION PRODUCTS. IN THE PHASE I PROGRAM, GAS MOLECULES ARE ABSORBED ON A COPPER ALLOY. STUDIES ARE BEING MADE OF HOW THEY ADSORB, OF CHEMICAL REACTIONS ON THE SURFACE, AND OF DESORPTION MECHANISMS. FROM THIS, RECOMMENDATIONS WILL BE DEVELOPED ON PASSIVATING THE SURFACE AND ON MODIFYING THE REACTIONS TO PREVENT THE FORMATION OF CERTAIN SPECIES. SUCCESSFUL COMPLETION OF THIS INVESTIGATION WILL TANGIBLY REDUCE THE INITIAL STARTUP TIME OF THE STORAGE RINGS, IMPROVE BEAM CHARACTERISTICS, AND REDUCE DOWNTIME.