Using state-of-the-art technology, cryomodules are vessels that contain superconducting cavities in a linear accelerator. Inside the module, liquid helium cools the cavities to -271° C, only slightly warmer than the coldest possible temperature. The superconducting cavities operate at these super-cool temperatures, pumping more and more energy into the particles that are moving at nearly the speed of light inside the accelerator.
Because the ILC will require 2000 cryomodules, the design team must consider two very important factors: manufacturability and cost. Achieving this perfect balance requires many design iterations, leading to several generations of cryomodules. Each generation builds and improves on the last version, moving closer to the right design for the ILC. Fermilab is part of an international team that is contributing to the 4th generation cryomodule design for the ILC.
The 4th generation group proposes moving the quadrupole magnet from the extremity of the chain of cavities to the centre of the cryomodule for stability reasons. The magnet will sit beneath one of the three supports, becoming a centre post in the most stable position of the vessel. Limiting movement inside the cryomodule is extremely important for maintaining a stable, steady beam line – a very delicate matter in a linear accelerator. Another important improvement is increasing the real estate gradient in the cryomodules by reducing the inactive space between the cavities. For the ILC, each cryomodule will contain eight cavities, linked together in a chain by mechanical interconnections. A longer cryomodule results in a longer tunnel and higher costs. Reducing the cavity space by just 1 centimeter will decrease the entire tunnel by 200 meters.
The 4th generation cryomodule design effort aims to have a complete drawing package ready to be sent out to vendors by the end of 2007. From that point, it will take approximately one year to assemble the first 4th generation cryomodule at Fermilab. Ultimately there will be a 5th generation cryomodule, which scientists expect will be a prototype for the ILC.