Gas System for ATLAS NSW Micromegas Detectors: Design and Validation Methods

1. GAS SYSTEM FOR THE ATLAS NSW MICROMEGAS DETECTORS: DESIGN ASPECTS AND ADVANCED VALIDATION METHODS FOR THEIR QA/QC NTUA T. Alexopoulos, E. Gazis, S. Maltezos, A. Antoniou, V. Gika, A. Giannopoulos, S. Karentzos, A. Koulouris, G. Koutelieris, P. Moschovakos , E. Spyropoulou National Technical University of Athens

2. Outline • Design aspects of Gas Distribution System of NSW Micromegas detectors (renewals, impedances, manifolds) • Simulation results and gas flow / pressure uniformity • Quality Assurance and Quality Control: gas leak test methods • Performance studies using emulates leak branches • Upgrade stages and Lock-in Amplifier (LIA) combined with FRL method • Baseline setup of Gas Tightness Station at BB5/CERN • Conclusions

3. The New Small Wheels of ATLAS Upgrade – Phase I Graphical representation of an assembled NSW From Ph.D of Ntekas

4. Overall drawing of the GDS – LM / SM Wedges • 16 gas channels should provide gas mixture to each NSW • Each channel provide gas either to two LM wedges or to two SM wedges • The gas inlet comes from the outer rim and the gas outlet goes to the inner rim. • The 16 gas channels are distributed as follows: • INNER (IP SIDE) MULTIPLETS • Ch. 1-4: LM1+LM2, Odd Sectors: • S1, S3, S5, S7, S9, S11, S13, S15 • Ch. 5-8: SM1+SM2, Even Sectors: • S2, S4, S6, S8, S10, S12, S14, S16 • OUTER (HO SIDE) MULTIPLETS • Ch. 9-12: LM1+LM2, Odd Sectors: • S1, S3, S5, S7, S9, S11, S13, S15 • Ch. 13-16: SM1+SM2, Even Sectors: • S2, S4, S6, S8, S10, S12, S14, S16

5. A typical gas channel configuration - SM wedges

6. Gas inlet details for LM wedge Mass Flow Sensor SHUT-OFF VALVE Impedance ZLM FCR “Trident” Manifold

7. Gas outlet details for LM wedge “Trident” Manifold Mass Flow Sensor

8. Indicative pressure drop P (mbar) Supply pipe line Rack Z in 0 Z out M P MFS Exhaust pipe line Rack Horizontal axis not in scale

9. Theoretical model of the proposed MM impedance objective (Dp)S1S2=8 mbar at Qo S1 C E S2 D, L Q Din,t 1 2 Capillary channel Lt Visualized flow, Ed. Japan Soc. of Mech. Eng. (1988) Sudden contraction energy losses Viscous losses Sudden expansion energy losses kLC is local resistance coefficient due to “minor losses” in the Sudden contraction. a is a geometrical factor expressing probable geometrical imperfections ( in sudden geom. a ~1). kLE is local resistance coefficient due to “minor losses” in the sudden expansion, calculated analytically based on Bernoulli’s equation and momentum theorem.

10. Simulation studies

11. Design of new impedances for 4 renewals/day FLOW RATES , DIMENSIONS AND ID CODES LM Wedge Q=10.44 L/h, 1.1Q=11.48 L/h D ch=500 μm, Lch=10.30 mm ZLM-500-10300-50-Q10 SM Wedge Q=6.84 L/h, 1.1Q=7.52 L/h D ch=450 μm, Lch=12.71 mm ZSM-450-12710-50-Q10 • The precision of the diameter of the channel has to be less than 10 μm, with 5 μm being technically achievable. • We have constructed a prototype of each type in NTUA and we also ordered some samples in an outside Machinery . • According to the results obtained with the previous impedances, their functional curves can be predictable.

12. Performance and evaluation tests in the Lab These 6 samples have been manufactured by a Lab equipped by CNC Machines

13. Average static pressure inside the MM Modules Indicative results for LM Modules using PipeFlow simulation program.

14. 3D visualization of the manifold

15. Leak rate predictions How we can predict the leak rate throughout a very small orifice from a chamber to the atmosphere ? Answer on this are given in the following report and the references there in: “Estimation of Gas Leak Rates Through Very Small Orifices and Channels”, written by Herbert J. Bomelburg in February 1977 for the Nuclear Regulatory Commission”. where: A is the aperture area Ψ is the throughout function p0 is the pressure inside ρ0 is the density inside pa is the pressure outside ρα is the density outside R is the specific gas constant a is an overall correction factor, mainly expressing the friction coefficient, f=64/Re if exist (we assumed a~1) g isthe adiabatic exponent of test gas (ratio of specific heats)

16. The NSW requirements for the MM Modules The Acceptance Limit for any MM Module (M) or Multiplet (MP) is defined by QL,LIM=Vx10-5 L/min=1.67x10-7xV st. L/s. This limit is the functional one, while the leak rate of a typical ,well-made Module, has to be studied. With st. L/h we mean: Standard Ambient Temperature & Pressure (SATM, T=25 oC , P=1.01325 bar) How to correlate and under which conditions (st. L/s) with (bar∙L/s) in leak rate specifications ? Measured by direct method (e.g. FRL) in st. L/s Measured by indirect method (e.g. PDR) in bar∙ L/s

17. Overview of the two Gas Leak Test (GLT) methods Pressure Drop Rate (PDR) Based on the ideal gases law Flow Rate Loss (FRL) Based on mass conservation principle B MFS1 MFS2 Qin Qout A

18. Basic setup of FRL method OMRON D6F-P0001A1 Full range: 0-6 L/h Repeatability: < 1 % F.S. or 0.06 L/h Repeatability (we measured): ~ 0.1 % Temperature range: (-10 – 60 oC) Systematic error caused only from slope b Cost: 55 € /pc for small quantity

19. Measurement procedure in C-FRL Should be closed after closing VA (in) ! • In the Cumulative FRL technique, typically 4 MM MPs in series can • be measured simultaneously. We need 5 MFS and 3 well tight shut-off valves. • The overall leak rate for well-made Modules is in average four times greater than • that of one MM MP.

20. Validation and Calibration techniques: 1st stage For testing the FRL method in the 1st stage we created emulated leaks using “Leak Branches” (LB) of different levels in the range from the detection limit up to two orders of magnitude. ΔV0 (display resolution at least 4.75 digits) p0: 0 (ambient) p3-0: 1-3 mbar Leak Branch NEEDLES Impedance array Z=6Zo

21. Leak rates measured as a function of pressure Consistent results at 1mbar Pred.: QL=0.197±0.080L/h Meas.: QL=0.196±0.002 L/h In case of leaking MM MP: The nature of the leak source could be identified from the pressure dependence !

22. A trick to find an upper limit of leak rate Let as assume a GLT result with leak rate QL,x compatible to zero. We can follow two steps by which we can verify the initial result and, as well as, we can give an upper limit to the leak rate: 1. Interpose to the MM MP’s input or output pipe a calibrated needle of type 32G. 2. Measure QL,m with the expected-known accuracy setting the upper limit: QL,x< QL,m

23. Results obtained by the FRL method Calibrated Needle 32G - CN1 (Dint=108 µm) Calibrated Needle 31G - CN1 (Dint=133 µm)

24. Results obtained by the PDR method The Calibrated Needles 31G and 32G have been measured in conjunction with a well - tight reference tube having volume of 1.05 L. The atmospheric fluctuations have been compensated by using a second DM. Calibrated Needle 31G - CN1 (Dint=133 µm) Calibrated Needle 32G - CN1 (Dint=108 µm) p=-10.2 t + 1.13 p =-5.04 t + 1.13

25. Baseline setup/stage-0 (overall configuration) Included only in the upgrade stage 1

26. Baseline setup/stage-0 performance • In the FRL method: • The repeatability of the Mass Flow Sensors is 1 % F.S. • It sets a limit on the sensitivity of the setup (k) for measuring the leak rate with respect to the acceptance limit of the LM1 (reference S/N =1). Stage 0: Sensitivity limit from k=1/6.5 (using 100 samples) to k≈1/20 (with better statistics and analysis) In the PDR method: The sensitivity depends on several parameters (accuracy in pressure recording, the temperature compensation, the time lasting of the measurement and the fitting analysis strategy based on the appropriate model QL(p) which is unknown in advance).

27. Upgraded setup: stage-1 performance • The upgraded concerns only the FRL method: • Implementing the Lock-in Amplifier (LIA) technique for recording the differential DC signal of the Mass Flow Sensors (reference: ATL-COM-MUON-2016-008). • The achieved improvement on S/N ratio depends on the signal level. Typically, we can reach a limit of k≈1/1000 and S/N improved by about 30. The analog dual phase LIA 5210 we used is a classical model available in NTUA. Gas Tightness Station – stage -1 Only the devices shown with the red outline have to be added to the baseline setup. Dual phase LIA e-choppers LIA Signal Generator Stage 1: Sensitivity k≈10-3 (>100 samples)

28. Upgraded setup: stage-2 • The upgraded concerns only the FRL method: • Replacing the two Mass Flow Sensors with Mass Flow Meters of much better repeatability (type MFM2020 from AXETRIS with repeatability 0.1 % Rd). For the nominal flow rate Q≈2 L/h the improvement in the repeatability allows us to reaching a limit of k≈1/1000 and a S/N improved by about 30. • Another improvement concerns the use of electro valves controlled by the DCS subsystem GTS Stage 2: Sensitivity k≈10-3 (>100 samples)

29. The LIA technique: Noise spectrum “Quiet region” • The DC or low frequency signals might be transferred in the “quiet region” (free from excessive noise) via modulation and then be measured by Lock-in Amplifier technique. • In the FRL method the DC differential signal of Mass Flow Sensors is modulated by using a dual synchronous electronic chopper .

30. LIA technique: the method In LIA technique, the signal with a superimposed noise and the internal lock-in signal are multiplied (synchronous demodulation). The principle of the method is based on the orthogonality property. Let us a sinusoidal signal: and an internally generated: The produced Phase Sensitive Detector output signal (VPSD) contains a low frequency level component proportional to the signal amplitude: noise If and , then DC signal The DC component is obtained by using a low pass filter.

31. Implementation by the dual phase LIA 5210 A Dual phase LIA 5210 in conjunction with homemade dual synchronous electronic chopper dual e-chopper The two chopped (square-wave) signals 5210 from SIGNAL RECOVERY used at NTUA In dual phase LIA the magnitude doesn't depend on the phase difference. In a sine-wave response LIA process the reproduced square-wave signal corresponds to the fundamental component in the Fourier expansion. Fundamental component

32. Typical leak rate analysis with a calibrated needle 32G GAUSSIAN FITTING RESULTS Mean=4.31 V Std=0.019 V Mean=4.95 V Std=0.032 V Reproduced differential signal Vs=(4.95-4.31)x6.66 mV=4.26 ± 0.25 mV Leak rate QL= (4.26 ± 0.24) mVx0.00328 (L/h)/mV=0.0140 ± 0.0008 L/h Therefore, a leak rate 2.7 times lower than the acceptance limit of LM1 MM Multiplet, measured with an accuracy of 5.7 %.

33. Data recording by the communication software • The LIA 5210 is supported by the ``Acquire Data Acquisition Software'‘, version 4.2. The device can be controlled remotely by this software while 4 ADC channels, having resolution 1 mV, are also available. • Using this software we recorded the variation of the differential signal VS obtained from CH1 out via the ADC1 input provided by the LIA 5210. VS at pressure p2 (p2>p1) VS at pressure p1 VS at pressure p1 stability≈0.3 % pressure ↑ pressure ↓

34. Evaluation tests and results at NTUA For the evaluation measurements we used an emulated leak branch (a needle ). In order to emulate low level leak rates we decreased the gauge pressure down to 0.25 mbar and to 0.15 mbar.

35. A view of the setup being installed at BB5/CERN • The installation of the Gas Tightness Station has been in April. • It includes the instruments and components referring to that we call stage-0 setup.

36. Fluctuation studies at BB5 GLT Station

37. Conclusions • The overall configuration of the Gas Distribution System has been finalized and the simulations are more realistic based on the routing solutions. The engineering drawings have been also completed. • The impedances for 4 renewals/day have been designed and we are investigating the CNC Machinery for their production. • Two methods for the gas leak test have been described and analyzed by • means of their sensitivity and feasibility, the classical one (Pressure Decay Rate) • and an alternative-novel method (Flow Rate Loss). • The method FRL seems adequate and having the required sensitivity • sensible to be used for a reliable Pass/Fail decision around the level of 10-6 • st. L/s. • We started installing the baseline setup (stage-0) of the Gas Tightness Station at BB5/CERN. As soon as the gas supply is ready we can proceed to functional tests.

38. Conclusions • The upgrade stage-1 or stage-2 on the LIA technique, has been implemented at NTUA and could be introduced at BB5. It is expected to improve the sensitivity for achieving k of the order of 1/1000. • The upgrade stage-2 (by replacing the two MFS) is also feasible improving the sensitivity to a similar level (k=1/1000). • Evaluation results at NTUA have shown the effectiveness of the LIA technique.