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

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)

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

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

Dust and fibbers on interconnecting brass bar MKD I/B1

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

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

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

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 generators to be blinded (self adhesive tape?)

Inspection team in action

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: 400 GeV – 30 min ramp up to Emax – 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: 400 GeV – 30 min ramp up – 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