Cryogenic helium valves deflection and relaxation in ESS linac cryogenic distribution system

Abstract The commissioning of European Spallation Source linear accelerator cryogenic distribution system revealed valve deflections, partly combined with lack of valve tightness. An optical method of noninvasive measurement of long-stem cryogenic valve straightness has been elaborated and compared with direct deflection measurements. The allowable value of the valve deflection has been estimated on the basis of mechanical analysis and the procedure of the deformed valve relaxation has been proposed and successfully implemented. The paper presents the method, its validation by the opening of one of the valve boxes on the ESS Cryogenic Distribution System and provides the limits of the method’s applicability.