Engineering analysis of the APT cryomodules

The superconducting radiofrequency (SRF) part of the Accelerator Production of Tritium (APT) linac will accelerate a 100-mA proton beam from 217 MeV to 1700 MeV. Since SRF cavities can accept protons over a wide velocity range, cavities with only two different betas are required; however, three different length cryomodules are required. A modular design was adopted that will reduce the engineering and design effort to produce these cryomodules. A final design of the APT Engineering Development and Demonstration (ED&D) cryomodule for a two-cavity β=0.64 cryomodule has been completed, and a single cryomodule will be fabricated by industry next year. The cavities will be cooled in a 2.15-K superfluid helium bath similar to the Continuous Electron Beam Accelerator (CEBAF) system. What sets the APT cryomodules apart is the high radiofrequency (RF) power that must be delivered to the cavities. The RF losses in the cavities and power couplers place a large heat load on the central helium liquifier. Minimizing these loads required extensive iterations of the power coupler cooling schemes and thermal shield. A spoke support arrangement was developed to keep the beam centerline fixed and to minimize forces acting on the helium vessel/cavity during cool down. Laminar flow through the cryomodule during clean room assembly dictated the use of a vacuum vessel with large top and bottom openings. Analyses were performed to ensure structural integrity under vacuum loading, while also minimizing vessel deflections which could impact beam centerline positioning. The structural/thermal analysis used to optimize the cryomodule design is presented in this paper