Chopper intervenctions in week 35 24 to 31082020

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Chopper intervenctions in week 35 (24 to 31/08/2020) Simone Chicarella, Giampaolo Piccinini, Cristiano Gagliardi

Chopper intervenctions in week 35 (24 to 31/08/2020) Simone Chicarella, Giampaolo Piccinini, Cristiano Gagliardi Suitbert Ramberger CERN, BE-RF-LRF

Simplified Block Diagram Chopper Amplifiers L O W L E V E L Cable

Simplified Block Diagram Chopper Amplifiers L O W L E V E L Cable ≈30 m Meander -30 d. B Cable ≈30 m -10 d. B & Splitter Freq Comp OASIS A+ O’scope OASIS AO’scope OASIS B+ O’scope OASIS BO’scope

First module failure (25/08) Chopper Amplifiers L O W L E V E L

First module failure (25/08) Chopper Amplifiers L O W L E V E L Cable ≈30 m Meander -30 d. B Cable ≈30 m -10 d. B & Splitter Freq Comp OASIS A+ O’scope OASIS AO’scope OASIS B+ O’scope OASIS BO’scope

Signals before the replacement A- B- B+ A+

Signals before the replacement A- B- B+ A+

Signals after the replacement B+ A+ BA-

Signals after the replacement B+ A+ BA-

Second module failure (28/08) Chopper Amplifiers L O W L E V E L

Second module failure (28/08) Chopper Amplifiers L O W L E V E L Cable ≈30 m Meander -30 d. B Cable ≈30 m -10 d. B & Splitter Freq Comp OASIS A+ O’scope OASIS AO’scope OASIS B+ O’scope OASIS BO’scope

Second module failure (28/08) Before After

Second module failure (28/08) Before After

Third module failure (28/08) Chopper Amplifiers L O W L E V E L

Third module failure (28/08) Chopper Amplifiers L O W L E V E L Cable ≈30 m Meander -30 d. B Cable ≈30 m -10 d. B & Splitter Freq Comp OASIS A+ O’scope OASIS AO’scope OASIS B+ O’scope OASIS BO’scope

Third module failure (28/08) One switching MOSFET failed (in RED). It was found in

Third module failure (28/08) One switching MOSFET failed (in RED). It was found in short-circuit (by Cristiano Gagliardi). Its related fuse acted (in BLUE) and opened. One possible reason is: ≈100 ns--> freq=10 MHz

Third module failure (28/08) 100 ns correspond to a repetition frequency of 1/100 ns=10

Third module failure (28/08) 100 ns correspond to a repetition frequency of 1/100 ns=10 MHz ≈1 ms Chopper is being operated OUT of specs. 10 MHz might overheat the MOSFET. We continue to work on improvements, and issues are followed up closely.