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Q5R4 corrector shorted to ground. Ongoing investigation

Q5R4 corrector shorted to ground. Ongoing investigation. Status at 18 June 2007 N. Catalan Lasheras. History of Q5R4. No electrical NC during manufacturing Electrical insulation tests done in SMI2 on 24/07/06 includes MCBY to MQY, Quench Heaters, ground, and each other.

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Q5R4 corrector shorted to ground. Ongoing investigation

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  1. Q5R4 corrector shorted to ground. Ongoing investigation Status at 18 June 2007 N. Catalan Lasheras

  2. History of Q5R4 • No electrical NC during manufacturing • Electrical insulation tests done in SMI2 on 24/07/06 includes MCBY to MQY, Quench Heaters, ground, and each other. • Results ok (EDMS 759062) • Installed in the tunnel on 2 August 2006 • Major movements of the D4-Q5 magnets and supports in 4R (NC 833372) • Q5 moved 9 mm under vacuum. Came back to 6 mm in atmospheric pressure • Interconnection open to check PIM. Ok. Closed again. • Re-test in vacuum foreseen. (?) • HV breakdown on circuit RCBYH5.R4B2 during ELQA at warm (NC 842369)

  3. MCB corrector short-circuited in Q5R4, EDMS 842369V. Chareyre • A discharge occurred during the electrical insulation test (voltage level at warm, 300 V) • Resistance to ground around 180 Ω (before pressure test in sector 45)After the pressure test, the problem has been deteriorated: around 2 Ω • A current of 70 mA is impressed in the circuit • Voltage drops across voltage-taps are measured, ground is used as a voltage pick-up • Short localized between the cold v-tap B and the coil BUT the v-tap is very close to the coil • The problem may be at the level of the connection of the coil Voltage pick-up Connection bus-bar to coil

  4. Measure repeated after the pressure test. R. Mompo • A third test confirmed that the short is on the lead side and not inside the corrector.

  5. What could have gone wrong? • Bus-bar of D4 and corrector very close. • They may have been put in contact after stretching D4 bus bar during the vacuum test.

  6. What to do? • According to the optics database not used for optics. Only orbit correction. Proposal: • Measure short after cool-down. • Monitoring the movement of the cold mass and the short could be a possibility • Open the interconnect after warm-up. Use and endoscope to check/confirm the contact • In the worst case a repair in situ seems feasible. • Insert extra insulation • Open the cold mass cylinder and repair connections

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