1. Cooling connections in the service gap Richard French The University of Sheffield

2. Overview Main topics covered today Services Gap Dimensions Access requirements for Welding Re-work Tangential thoughts……….. – Does the TDR lock us into a specific service gap size – Access will dictate tube wall size eg poor access = thicker wall tube – Purge gas – how to get it to the joint that we are welding with overpressure – All applies to rework except Tube end preparation for welding Cutting out old BACK TO ACCESS REQUIREMENTS

3. Joining and weldability 316 CP2 Its pretty easy once you know how We have made thousands of tube welded joints in a range of materials both commercially, commercial research and have pushed R&D for TIG beyond commercial requirements to date. We evaluate welding machinery for companies using our techniques and equipment designed in-house. TIG orbital welding limit is 200μm Have not tried to reduce further Butt welding successful on both 2mm and 1/8” tube Diameters are 2.0mm and 1/8” so standard fittings work without modification Brazing is ok but untested as not needed to make this joint as never dissimilar material Can join this material without much effort or thinking. TIG orbital welding limit is 125μm Have not tried to reduce further Butt welding successful on both 2.275mm and 1/8” tube Diameters are 2.275mm and 1/8” so standard fittings work on the 1/8” tube but are hopeless for the smaller OD. 125μm wall in small OD is not for in-situ joining or ……….. We need to make the tube preparation very good but I don’t see this happening yet.

4. Christophe Bault – CERN 6/2/14

6. Service Gap Dimension (z=91mm) Robert Gabrielczyk - RAL

7. Detail We should not get hung up on the gap dimensions in Z (photo) We should worry about the position of the tube in relation to the end of stave eg – push the tube further out to the EC’s to increase clearance NOT WORRIED YET for installation WORRIED IF WE NEED TO REWORK in the sense of a service intervention post installation

8. Access requirements for welding 5.5m cable length from power supply to weld head WPS qualified for this length Not worried about RF from machine – maybe add a shielded cable – weld head ok. G – Add another 80mm as we need to move the cassette in and out the head C – Add another 10m as we need to add support collets for in-situ work to suit tube type better (tube joint alignment and heat sinking) Need to be realistic and work out what tubes can go where when held by hand. Can we use jigs – doubt it. IM tasked with a measuring system = simple point to point feeler – check if ok for 3D. If in doubt we use filler rings to support the tubes. Not tested at all yet as will be very bespoke

9. Re-work of connections Things to consider I am not considering re-work of 125um CP2 Ti in-situ Here I consider 200um CP2 Ti rework in either 2.5mm OD or 1/8” OD We can not weld on a weld – we can but it is very bad practice (annealing) Cut sections out and replace Electrical break – capacitance induction or transient voltage Gas purge must be present during re-work. Can we add valves to the system to prevent filling the entire volume? Tube ends must be flat and parrallel with excellent surface finish and all oxide removed, no burrs, no swarf or dust in the bore – Debris filtering can be used