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If you want superconducting cavities (see SRF Intro on MCC wiki) at 2K, such things can't be next to 300K air - all the liquid helium would boil. Instead the cavities in their helium vessels (titanium jackets that allow an accumulation of liquid helium around the cavities) are deep within a cryomodule. The components of a cryomodule are progressively cooled from 300K room temperature (the exterior vacuum vessel) to 2K liquid helium around the cavity.
Photo of an LCLS-SC Cryomodule being unloaded at the sector 10 adit in preparation for installation in the SLAC accelerator housing:
Cryoplants & Distribution System
The LCLS-SC Cryogenic System consists of two cryoplants in one very large building just north of the klystron gallery sector 4, the distribution system (piping to distribute helium gas at various temperatures), and cryomodules. I highly recommend the Cryoplant Overview by Eric Fauve 8/27/21.
The output of the cryoplants is gaseous helium of various temperatures in different pipes in one large pipe called the distribution line which runs across the north gallery road. The pipe feeds into the two distribution boxes which then feed into two distribution lines that goes into the accelerator housing. One goes west and feeds into the pipes (cryo lines) in L2B. At the west end of L2B is an "end cap" which transitions the cryo lines back to the distribution line which bends up to the ceiling to go over BC1B before descending and joining the L1B "feed cap". The cryo lines go through L1B then through the end cap back to a distribution line that goes over the laser heater before going to L0B. At the far west end of L0B is an end cap where some of the cryo lines turn around.
The output of the downstream distribution box goes downstairs to the L3B feed cap. In the middle of L3B is a vacuum barrier - a location with vacuum equipment for the insulating vacuum. At the east end of L3B is an end cap where some of the cryo lines turn around.
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This slide shows a drawing of the cryomodule cross section and a photo of a cryomodule cold mass before it was inserted into the vacuum vessel. At the top right is a cross section drawing of a cavity in its helium vessel showing the cooldown line feed ports at the bottom and the chimney connection to the two-phase pipe at the top.
The cryo lines' functions are as follow:
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The various cryo lines are shown in cartoon form on this screen:
which can be reached from lclshome, then any of the LxB cryo boxes, then select a specific cryomodule.
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