1. SCU Layout Concept - Minimal Segmentation Joel Fuerst (ANL) SCU 3-Lab Review Meeting Dec. 16, 2014

2. SCU 3-Lab Review Meeting, Dec. 16, 2014 Introduction “Segmentation” refers to the layout strategy for connecting an array of individual cryostats. The downtime associated with removal of an individual cryostat is highly dependent on the layout. Component reliability and redundancy contribute to the expected frequency of cryostat removal. System cost increases with increased segmentation. compared to

3. SCU 3-Lab Review Meeting, Dec. 16, 2014 Minimally segmented layout concept Individual 5.5-m cryostats are arrayed in some number of continuous multi-cryostat strings. Strings are separated by 1 or 2 room-temperature self- seeding sections. Within a string, cryostat interconnect strategy is similar to the LCLS-II SC linac. The cryogenic distribution system is internal to the cryostats except at a warm bypass or at the cryoplant interface.

4. SCU 3-Lab Review Meeting, Dec. 16, 2014 Cryostat geometry The vacuum vessel is standard 16” pipe. Thermal radiation shield is cooled by helium gas at ~50 K. Cold mass is cooled by saturated LHe at 4.3 K. Flanged sub-assemblies contain independent conduction-cooled current leads for each magnetic element. Cold mass Thermal shield Vacuum vessel Current lead/ instrumentation assemblies Retractable inter-cryostat vacuum bellows

5. SCU 3-Lab Review Meeting, Dec. 16, 2014 Cold mass geometry Three 1.5-m SCU magnets plus quads, phase shifters, and bpms (not shown) are aligned to a rigid strongback. SCU magnet cooling channels are fed by a LHe reservoir pipe running the length of the string. Other elements are conductively cooled at 4.3 K. Helium pipe Magnet with Horizontal field

6. SCU 3-Lab Review Meeting, Dec. 16, 2014 Alignment/subsystem access Magnetic elements are precision aligned to the strongback. The cold mass assembly is suspended from the vacuum vessel using adjustable low-heat-leak supports. Cryostats can be independently aligned within a string due to flexible interconnect elements. Beam-based alignment is possible via x-y motion control systems located at the cold mass and/or the cryostat supports. Access to current leads, quads, phase shifters, bpms is possible via access ports in the vacuum vessel/thermal shield when the cryostat string is warm and vented.

7. SCU 3-Lab Review Meeting, Dec. 16, 2014 Refrigeration system A cryogenic transfer line connects the refrigerator to the SCU string end boxes. Cryogenic bypasses are used at other warm sections. Static heat load of 2 W/m is a reasonable design goal. Upstream String 1 Downstream String Upstream String 2 Surface Tunnel Refrigerator Coldbox Helium Compressors Gas Storage Transfer Line Bypass

8. SCU 3-Lab Review Meeting, Dec. 16, 2014 Refrigerator example Some system components as well as buildings and utilities are pre-existing at SLAC.

9. SCU 3-Lab Review Meeting, Dec. 16, 2014 Summary Factors affecting the choice of layout strategy include component reliability, maintainability, and cost. The minimal segmentation option can be summarized as follows: – Primary Advantage: Lower capital and operating system costs are possible due to simpler cryostat geometry, the absence of a separate, external distribution system, and smaller refrigeration requirements. – Primary Disadvantage: Removal of any individual cryostat requires a room-temperature thermal cycle of the entire undulator string.