Design of the Thermal Shields for the New Improved Version of the TESLA Test Facility (TTF) Cryostat

Abstract

One of the principal goals of the ongoing TTF project is to produce prototype low cost and reliable cryomodules meeting the stringent requirements for TESLA. The first cryomodule was assembled and tested at DESY. The experience gained during the design and the commissioning suggested new solutions to improving the technical design. The most important improvement is the design of the new thermal shields at 4.5 K and 70 K. In this design the cooling helium pipes are directly welded to the aluminum shields. This solution simplified the technical design of the entire cryomodule and indicated some issues that needed study to verify the behavior of the new structure during cooldown and operation. The principal aspect studied has been the procedures necessary to avoid stresses and deformations produced during the cooldown which might damage the shields. The solution found also prevents the typical deformation induced by the welding and makes the production pre-alignment easier. Shields will be welded through small aluminum fingers that reduce the resistance section of the joint, while increasing the elasticity, unloading the welded joints and preventing possible damage during the cooldown.