AT/CRG/cd 1 DFBX Low Current Lead Chimneys Consolidation May 16th 2008

AT/CRG/cd 2 Condensation Issue : 600 A and 120 A current lead chimneys Risks:  Presence of ice/water on the G10 support will create electrical hazard.  Ice will grow on the top of the cryostat potentially resulting in equipment structural damage Consequences:  When the DFBX LHe vessel is filled with liquid helium, the cryostat top plate interface with the current leads exhibits extremely cold temperatures (<10C).  Generate condensation even with maximum heat deposed on the flag heater, EH893.  We cannot operate the 600 A and 120 A current leads with the given configuration. Long term consolidation of every low current leads is requested. Root Causes:  The thermal gradient along the current leads is inadequate: inefficient baffle systems.  Tuning of the helium vapor flow (see relocation of TT893s).

AT/CRG/cd 3 Solution: Provide a constant temperature distribution by heating the four chimney flanges Temporary solution:  80 W band heaters R5, L8, R8 and L1.  DFBXG: with temperature regulation L8).  DFBXA and DFBXH: with insulating blanket. Final solution:  120 W customised heater (6x20 W cartridge heaters).  10 mm free space around the 8” Standard Conflat Flange.  Special case for the DFBXG (S78). Difficulties:  Space requirement and Access to install the heaters. Feasibility studies:  Equipment:  Cartridge heater : 6 x 20 W  1 x Pt100 with regulator  Add four power supplies for the four chimney heaters  Prototype by Lionel Metral

AT/CRG/cd 4 Heater around the low current lead chimneys

AT/CRG/cd 5 Space and access requirements

AT/CRG/cd 6 Cross section of the DFBX

Flow schematic of the DFBX

AT/CRG/cd 8 Flow schematic of the DFBX

AT/CRG/cd 9  Install heater brackets around each of the four low current lead chimneys.  When needed: move the 600 A lead power cables in order to allow a 10 mm space around the four DFBX low current lead chimney flanges to ease the heater assemblies.  Every action must be reviewed prior to cable disassemblies in order to ensure that the re-assemblies will be trouble free. A procedure will be generated.  The thermal resistance must be minimized.  Electrical braids can be installed for few (6) DFBXG cable connections.  Cu spacer (entretoises) can be used.  Note that the cable route of the DFBXG is more constringent (DFBXG cable route designed as a prototype). Recommendations