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from ANNEX 02 to NCR/FM/INFN/RM2/003

Preventive Cuts (Pcut) Procedure. originally thought to prevent delaminations in TVAC only performed on 8 tower0 trays on W-side (8layers). 26.5 cm/tile 4.24 m/layer ~34 m total length of tower0 preventive cut. from ANNEX 02 to NCR/FM/INFN/RM2/003. Bubble Cuts (Bcut) Procedure.

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from ANNEX 02 to NCR/FM/INFN/RM2/003

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  1. Preventive Cuts (Pcut) Procedure • originally thought to prevent delaminations in TVAC • only performed on 8 tower0 trays on W-side (8layers) • 26.5 cm/tile • 4.24 m/layer • ~34 m total length of tower0 preventive cut from ANNEX 02 to NCR/FM/INFN/RM2/003

  2. Bubble Cuts (Bcut) Procedure Small (<2mm) cut far from bias lines (>1mm) using an edged scalpel Insulation test (OL) with an ohm-meter between tray and shield plane Used for tower0 trays and # TowerA trays Estimate of total bubble-cut for tower0 = 17layers x 2bubbles x 2mm <~ 7cm

  3. Tower0 trays summary chart

  4. Conclusions – risk assessment • 0 short on shield lines • 4 HV short on trays Pcut and Hand-Sanded W • 23 layers OK on HV line (6 Pcut, 15 Bcut) • 27 layers OK on shield line (8 Pcut, 17 Bcut) •  all shorts due to W whiskers generated from tiles hand-sanding which entered long, deep Pcuts – such whiskers were actually observed • on towerA: • NO Pcuts • W tiles are etched and primed, therefore very flat, clean and whiskers-free • Bcuts are superficial (see procedure) • Let’s calculate anyway a conservative HV-short probability: • a HV short would cause 1 ladder loss (on tower0 trays with HV-short we disconnected HV resistors on MCM boards for all 4 ladders to avoid current flow) Prob(1ladder-loss/Bcut) = 4 / 34 m x 2mm = 0.23 10-3 , i.e. 1ladder-loss every 4250 Bcut or 1 ladder with HV-short every 2150 ladders (assuming 1 Bcut every 2 ladders)

  5. Conclusions – schedule constraints List of available trays 3 trays without Bcut and MCM pocket deep enough to hold MCM  GA flow will be slowed until new trays are available without Bcut

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