Construction, Commissioning and Cryogenic Performances of the First Tesla Test Facility (ttf) Cryomodule

A principal goal of the ongoing TESLA superconducting linac project is the production of affordable cryostats that still meet stringent requirements for alignment, vibration and heat leak. Each cryostat contains 8 superconducting RF cavities cooled to 1.8 K, a quadrupole magnet package cooled to 4.5 K, thermal shields cooled to 70 K and 4.5 K, active and passive magnetic shielding, cryogenic service pipes and all associated instrumentation. The axes of the 8 cavities must be aligned to the ideal beam axis to within ± 0.5 mm and those of the quadrupoles to within ± 0.1 mm. Additionally, the vertical mid plane of the quadrupole package must be aligned to the vertical direction to ± 0.1 mrad. These alignments must remain fixed after cool down and during operation. The cryostat must be designed so that there are no resonant vibration modes near the 10 Hz operating frequency of the accelerator. Although dynamic loads associated with the operation of the RF and the beam dominate the heat load, reasonable efforts to reduce the static heat leak into the cryostat are necessary. The first of these cryostats has been tested in early June, 1997. This paper reports on the assembly of the cryostat and its performance during cryogenic and beam testing. Alignment, heat leak and vibration data are among the results discussed. The impact of the cryostat on the performance of the superconducting cavities is reviewed. Planned improvements in the cryostat design are also covered.