Development, design and installation of multichannel transfer lines at W7-X under extreme geometrical constraints

After the completion of the third experimental campaign in 2018 the stellarator fusion experiment Wendelstein 7-X (W7-X) was further completed with ten actively cooled divertors and ten Cryo-Vacuum-Pumps (CVPs). The cryo-panels and the thermal shield of the CVPs are cooled with supercritical helium (He) at around 4 K and with liquid nitrogen (LN2) at 80 K respectively. A set of 4-channel transfer lines with actively cooled thermal shield was developed and implemented:(1) one main transfer line (HTL, length ca. 55 m) for transferring the cryogenic fluids from the refrigeration system to the distribution box (CVB) and(2) ten short transfer lines (KTLs, length 12 m to 16 m) connecting the distribution box (CVB) to the supply ports on the W7-X cryostat. Beyond the usual requirements for cryogenic vacuum super-insulated transfer lines, the HTL and KTLs are required to respect the severe geometrical constraints posed by the limited installation space. Welding is possible only at certain locations and there was the need to circumvent support structures and many diagnostics. This resulted in routing changes in all three directions within a few meters. The solutions adopted for the development, the design and the installation results of HTL and KTLs lines are illustrated and discussed.