1. LBDS YETS activity report Viliam Senaj MKD meeting, 19/01/2016

2. Maintenance activities on MKD’s Replacement of perforated side panels by non-perforated ones (to reduce dust penetration into the dust sensitive top compartment with capacitors): B1+B2 - done Adding an insulation foam between top and bottom compartment: B1+B2 - done Swap of GTO stacks in order to reduce peak current difference between 2 branches - done MKD E/B1 st.A with MKD E/B2 st.A (both Westcode) MKD M/B1 st.A with MKD A/B2 st.A (both ABB) Cleaning of MKD generators: B1+B2 – done Endoscopic inspection after cleaning – B1 done: some dust and fibers observed but also 4 major problems found: Metal stripe in a sensitive region of GTO stack in MKD M/B1 st.A (swapped during YETS) Incorrect position of cooling fan frame on several generators Important quantity of fibbers/dust on the capacitors interconnecting brass bar of MKD I/B1 – dry cleaning? Missing washer between GTO stack and copper bar MKD E/B1 st.A (swapped during YETS) Endoscopic inspection of filtering capacitors - small leak found (less than on MKB)

3. Metallic piece in sensitive region – MKD M/B1 st.A

4. Non-correct position of cooling fan frame MKD N/B1MKD L/B1 MKD E/B1 Increases risk of electrostatic charging (by air flow) of plexiglas insulators of stack A return rods and thus increases risk of erratic

5. Dust and fibbers on interconnecting brass bar MKD I/B1

6. MKD E/B1 st.A – washer between stack and copper bar not installed back after intervention

7. Maintenance activities MKB’s Replacement of 3 stacks GTO due to sw_ratio evolution: MKBH A, B, D/B1; by mistake the stacks were first replaced on B2 (confusion of FSU with MKD/B1 which is in UA 63 while MKBH/B1 is in UA67) Endoscopic inspection of MKBH/MKBV B2 (UA63): – brown traces (oil drops?) on main capacitor HV insulator found; not easy to clean with alcohol… More efficient solution to be find in lab (demineralised water?, acetone?...) and to be cleaned … Measurements of electrical parameters of filtering capacitors (important traces of leak (?) found last year): – no variation found compared to values measured during TS – compared 3 MKBH, 2 MKBV and 1 MKD filtering capacitors Increased clearance of filtering capacitor from conductive surfaces – added washers and changed connection layout

8. Traces on MKBH HV capacitor, filtering capacitors leak(?)

9. Conclusion from inspection (MKD/B1+MKB/B2) More rigorous inspection of intervention team to be done (preferably to include Stephane H. into a team) Full body protection clothe (like for a clean room) to be used by intervenants to avoid pollution of generator by clothes fibres Dry cleaning to be avoided Still some (small) holes on top aluminium plate of MKD @MKB generators to be blinded (self adhesive tape?)

10. Inspection team in action

11. LBDS tests after YETS Generators with GTO stack replaced/swapped during YETS: slow control (soft) + HV test + sparking test: MKD: A + E + M/B1; A + D + E/B2 MKBH A + B + D/B1 + B2 > 2 ES up to 7.1 TeV prior to reliability run (comparison data) “Short cycle test” ~ 4 days: 1h @ 400 GeV – 30 min ramp up to Emax – 4h @ Emax – 30 min ramp down; initial “conditioning”: 1 day Emax=6 TeV, 1 day Emax = 6.5 TeV, 1 day Emax = 7 TeV; 1 day Emax = 7.1 TeV “Long cycle test” ~ 4 days: 3h @ 400 GeV – 30 min ramp up – 12 h @ 7.1 TeV – 30 min ramp down DC test > 2 days at 7.1 TeV 2ES with update of settings/limits if necessary Cooling conditions during “reliability test” have to be ensured: UA’s ambient temp < 24 deg