TRT operation scenario

1. TRT operation scenario • Gas Leaks status • Towards 100 kHz running

2. Active gas leaks: test results • Tests done just after the run. • All leaks are at the exit of the detector. • Color coding corresponds to a size of the leak. • No change in leak status before a repair work started (~3 months.) Barrel M3 M2 M1

3. Active gas leaks: test before and after repair EC-A Before After EC-C

4. TRT leak summary • Leak repair is not possible for the barrel TRT. • Leak repair work including a preventive one has been carried out for both ECs (finished 13th of June, all ECs closed, no more interventions are planned). • Few large and small leaks were repaired but some situated in inaccessible areas. • For the cases when a leak was not fully repaired the installed tooling allows to bring a regulation point close to the detector what makes easy to control the leak rate. • A presence of O2 (source of Ozone) in the active gas mixture is mandatory to ensure stable operation. • Amount of O2 (3% at base line mixture) is under revision now but it does not seem that it can be significantly reduced. • We shell expect that the leaks will get worse with an increase of luminosity. • For the End-caps repair work allowed to move the regulation point close to the detector • After gas system upgrade we shell expect better leak rate regulation and operation stability. By how much- still to be answered!

5. Operation scenario • Exact operation scenarios to be studied and discussed. Here are some preliminary thoughts . • Start physics data taking in 2015 with Xe-mixture – still to be confirmed if it is possible at a reasonable price. • Any way the limiting factor of “for how long” is amount of money allowed to be spent for Xe (current price is ~ 8.6 CHF/l). • When losses will become inacceptable we will start using Ar-based mixture in some parts of the detector, which have minimum impact on physics. • Maximum fraction of the detector running with Ar-mixture before a complete change of the active gas is still to be defined. What our choices depend on?

6. Start of the RUN2 with Xe-mixture Configuration in p-Pb run) HL/LL ratio Direct Xe-mixture flow ~1-1.3 l/h Ar-mixture All other large leaks were under regulation Total Xe loss at that period was ~170-200 l/day • Problems: • Did not manage to make good gas exchange in the barrel modules 9-12. • Group of modules type 1 (29-32) has 2 holes in the pipes (difficult to control) • Gas gain in wheels 1 and 6 was may be by 10% less. • Very difficult to keep other parts under control (env. gas breakthrough, accumulation of N2, large Xe losses – hope to be better in 2015 run). • Clearly see Ar shaping issue for the EC.

7. Start of the RUN2 with Xe-mixture • Worst scenario: • We can not control EC A wheels 1, 4 and 6. • We can not control groups of modules Type 1 9-12 and 29-32. • In that case gas losses will be ~240 l/day: • direct ~ 5*1.2 = 6 l/h • Indirect ~ 4 l/h (regulation require some gas to come out (many lines) • 7.2 m3/month * 10 months =72 m3 => *8.6 CHF/l = 619 kCHF • Best scenario: • All modules can be controlled • In that case gas losses will be ~140 l/day: • Indirect ~ 6 l/h (regulation require some gas to come out (many lines) • 5.2 m3/month * 10 months = 52 m3 => * 8.6 CHF/l = 447 kCHF • Both evaluations have large uncertainties. • ATLAS will give us the limit. • But two things should be done. • Accumulate maximum Xe in 2013 and 2014 + what comes in 2015 • Find chipper Xe (Russian supplier)

8. Ar-mixture: some constrains to be taken into account Ar/CO2/O2 70/27/3 Straw efficiency >95% (the same as for Xe) s=130 mm Xe Drift-time accuracy, mm Ar Working point!? Voltage, V Unbiased residual Biased residual In the Barrel and ECs gas gain is limited by cross talk The limit is ~2.5*104 For wheels type B this effect might be stronger!

9. Absence of Ar-shaping in some EC boards (greenareas)

10. Effect of Xe shaping for Ar mixture Ar/CO2/O2 70/27/3 Signal with after pulse Average signal for beta source at GG =2.5*104 Maximum probability for after pulse as a function of gain. After pulse probability function for different GG

11. Background suppression as a function of ETHA • Shell we preserve TR functionality in the calorimeter crack region? • What ETHA regions are the most important for trigger?

12. Operation scenarios Candidates to be given up in 2015

13. Questions to be discussed and answered • The list should be continued and by the end it shell be the input for MC studies. • What modules we shell start operating with Ar first? • Shell it be a large step (like 1st layer of barrel modules) or one by one (MC sample production)? • Does it make a sense to leave only outer layer of the barrel TRT with Xe. • Is it better in the barrel to go layer by layer or better turn on Ar-mixture in some blocks of modules. • Does it make a sense to operate Barrel with Ar mixture and ECs with Xe? • Does it make a sense to have only one EC (one barrel sector, part of the barrel …) with Xe mixture? • Which fraction of the detector should be considered to stay with Xe mixture before turning everything to Ar. • What constrains are to take any decision (FE electronics settings, Compression in RODs, recalibration, MC samples for physics, ?????) • ………………………………….??????????? • Discussion!