Ensuring a successful TPC production

1. Ensuring a successful TPC production • Design • Quality Assurance (QA) • Quality Control (QC) Sven

2. Hypothetical Failure Scenarios • As magnetic field is turned on four of the TPC instantly fail. Cause: Ferromagnetic screws used to secure field cage resistors in last four TPCs, after we ran out of other screws. Actual problem: design stage - no clear agreement on exactly which screws to use. • During phase II, as luminosity increases, gas purity deteriorates. We find we need slightly higher drift velocity and HV to get a good signal. Three of the TPCs spark at the new setting and can no longer be used. Cause: Rough specs on three individual field cage ring. Actual problem: QC procedure did not specify passing criteria for spark testing of field cage. Only nominal field value used. QA did not specify visual inspection of rings. • Three of the TPCs have a lower signal. We have to flow more gas to recover, and run out of funds, due to the expensive gas vendor at KEK. Cause: there is food grease on three Kapton shields. Log reveals these three TPCs were assembled by one particular student. Actual problems: QC: Did not measure outgassing of all final field cages. QA: Did not prescribe use of gloves. • Such failures are very typical in experimental HEP(!) • Minimize or avoid through careful • Design – what do build • Quality Assurance (QA) – how to build • Quality Control (QC) – how to test

3. Design: All aspects of design should be • Agreed on – shown in production meeting • Approved– by all three Ph.D.s: Igal, Peter, Sven • Documented– on Wiki • Exact design specification (shop drawing, design file, part number, web page link or similar) • Date approved, and by whom • QA/QC procedure is part of design, must also be agreed on, approved, and documented • We did some rough documentation of prototype design here: https://wiki.phys.hawaii.edu/bin/view/BEAST/TechnicalDocumentation • Need more detailed page for production

4. Quality Assurance (QA) • We need written instructions for how to build each part • There should be a checklist on a printed piece of paper, where people checks off each production step, put initials, and date • There can be multiple people signing off • Example (rough) for FE DAQ boards: • Procure circuit board from vendor A • Vendor B loads components • Send to LBNL for chip loading • Glue chip with epoxy of type TBD • Wire bond • Ultrasonic cleaning • Ship back to Hawaii • Characterize FE chip • Assemble onto field cage structure • As the TPCs get integrated, the QA/QC sheet for all parts get put into a common folder (one folder per TPC) • There can be separate levels of sheets. For instance, characterizing FE chip may get a separate QA sheet with more detail. And one top-level sheet per TPC.

5. Quality Control (QC) • We need written instructions for how to test each part • There should be a checklist on a printed piece of paper, where people checks off each test step, put initials, a few key summary tests results, date, location of test data • Detailed test data should go into a common location on dcube server • [As the TPCs get integrated, the QA/QC sheet for all parts get put into a common folder (one folder per TPC)

6. Final Comment • What you just heard may sounds pedantic • But, such steps were crucial for construction of complex detectors systems in the past. • E.g. ATLAS pixel detector • If production is well documented, you can often figure out cause of failures by studying the log books carefully, and correct procedures in time • If not well documented, failure is likely