Status of North Area Target (TCC2) & prospects EATM 28/07/2015D. Grenier1 Targets (T2, T4, T6 and T10) replaced in 2014 during LS1 (+ 4 spares) Previous target support positioning mechanism relied on mechanical indexing for vertical positioning of targets Oil leaks and unavailability of spares prompted decision to design new mechanisms based on use of stepper motor technology, LVDT and Burgess switches, as used for LHC collimators etc. In order to ensure system would hold position in the event of motor failure a trapezoidal lead screw was selected for the vertical drive mechanism (non backdriveable) New targets operating since end of LS1 Background EDMS

EATM 28/07/2015D. Grenier2 Problem Noted by CCC operators starting from May 2015 Stepper motor for T2 losing steps when moving target in lower positions – It later affected T6 but not (for the moment) T4 (and T10) This implied motor was unable to overcome frictional torque of the mechanism in certain positions As reducing motor controller set speed gives higher motor torque – it was still possible to move very slowly Decision:  Block the Targets in position #2  Start the investigations on the failure mode

Initial Investigations In TCC2: – Visual inspection of T2-4-6 – Put (rad hard) grease on T2 lead screw – Swap motor controller Outside radiation areas – Calculation review of frictional torque (torque margin of motor-gearbox less than originally thought) – Manual torque measurements on spare targets – Operational testing of spares (200 cycles) EATM 28/07/2015D. Grenier3

Rapid intervention solution (during SPS scrubbing runs) To reduce torque requirement to move target, a counterbalance spring system was developed as quick add-on Testing on spares showed significant torque reduction Springs fitted to T2 + T4 Torque reduced but cycling of T2 showed torque increasing with cycles Any further modifications will require exchange of complete target EATM 28/07/2015D. Grenier4

Further investigations Spare target stripped down to assess friction due to guidance, bearings, lead screw/nut Visit to specialist lead screw manufacturer Trials without grease Discussions with bronze suppliers Ongoing activities: – Review of design elements in collaboration with EN–MME – Review of materials / lubricant /environment compatibility in collaboration with EN-MME EATM 28/07/2015D. Grenier5

EATM 28/07/2015D. Grenier6 Modifications planned for BAC T2-4-6-(10) Optimise lead screw and nut by selection of materials and lubricants to reduce friction over lifetime in NA environment 2.Optimise bearings and their lubricants 3.Increase ratio of reduction gearbox to increase total input torque 4.Increase clearances around support shafts 5.Remove springs

Proposed Strategy EATM 28/07/2015D. Grenier7 Order the required material and components to modify the existing spares Carry out extensive pre-installation trials – Validation tests of material coupling in radiation environment under study – Analysis/expertise of irradiated T2 target as soon as it could be removed from TCC2 (before winter stop) to provide failure mode(s) Preparation for intervention: modify 4 spare targets for replacement of T2, T4 and T6 Intervention in TCC2 to replace T2, T4 and T6 (approx. 1 day/target) Upgrade the presently installed targets from TCC2 as further spares, following ALARA principle NB: T2 can still be moved out of beam (NB: in between plates!!) if required by physics

Summary & conclusions Several modifications of TCC2 targets mechanics being considered to solve technical issues encountered during 2015 operation Material procurement and further check impose a change not earlier than during YETS Expertise of presently installed targets (especially T2) in radioactive lab mandatory to confirm the validity of the changes EATM 28/07/2015D. Grenier8

Spare Slides EATM 28/07/2015D. Grenier9

EATM 28/07/2015D. Grenier10 Replacement of BAC T2-4-6 ? WDP: approximatively 1 day/Target Shield containers to produce, for future expertise Spares to adapt to the new version, test and align New solutions in a simplified system tested under radiation (CHARM or TCC2) until YETS?? Date of replacement (YETS)?

EATM 28/07/2015D. Grenier11 Schedule

EATM 28/07/2015D. Grenier12