Reaction on the review document Gossip_091215x dd 11-1-2010 of the Gossip R&D proposal

1. Reviewers • Tatsuo Kawamoto • Werner Riegler • Mike Tyndal • Norbert Wermes Reaction on the review document Gossip_091215.pptx dd 11-1-2010 of the Gossip R&D proposal Reviewed by Atlas Upgrade Steering Group • Reaction by • Harry van der Graaf • Fred Hartjes • Nigel Hessey Discussion on the review of the Gossip R&D proposal CERN, February 8, 2010

2. Points of discussion distilled from the review document Gossip_091215.pptx The committee would like to have more details about advantages and disadvantages of Gossip • Replacing Si with gas does not substantially reduce the material budget • What’s the point with dE/dx? How does it work? • Do we want TR, how would it be achieved? • What’s the advantage of getting rid of delta rays? • Gaseous detector is not better with neutrons • Why is the power less, there is more digital power? • Power reduction only applies to analogue part (<50%) • Is InGrid technology cheaper than bump bonding? • We will not address these points as such, but in the framework of the answers to the other points of discussion the committee brought forward

3. Scope of this presentation • Focussing on subjects specific for Gossip technology • Ignoring generic subjects like • Optical links (Iflink) • Powering (optical) • Cooling technology (CO2) • Mechanical support • Questions classified in general subjects

4. Questions/ comments by the committee

5. Classes of questions • Working point • Target regions • Performance • ageing, rate tolerance, efficiency, delta rays, track segment info, field distortions, X/X0 • Sparking • Frontend electronics • Noise level, threshold, power consumption, readout • Photolithography • Production of Ingrid • Miscellaneous • Grid capacity, cooling • Organization of the Gossip R&D • Collaboration, milestones

6. 1. Working point2. Target regions • Working point • Grid voltage • gap width • cell size • gas mixture • shaping time • ionization • What are the target regions for putting the Gossip technology? • => formulate essential goals to be met for Gossip working in these regions • Outer GridPix detector with 50% of silicon material?

7. 3. Performance • Ageing • Expectations • How to study? • Rate performance • Field distortion by ions • Rate limit • How to study? • Efficiency • Delta rays • Why is it good to get rid of them? • Compared to silicon • How to deal with track segment info? • Implementing L1 trigger? • Implications on RO rate? • Cooling • Required capacity compared to silicon? • Why dependence on operation temperature? • X/X0 • In reality 1.5 – 2% • What’s the difference with silicon and where does it come from?

8. 4. Sparking • Protection layer • What materials are considered? • Are there pinholes, can they cause damage, how likely? • Temperature sensitivity? • Pulse height dependence on layer thickness and resistivity? • Effect on rate? • Omitting Si3N4 layer in case of layer on InGrid or when using TwinGrid? => all these questions to be answered at session 6. (photolithography) • Demonstration for large system • Sparking rate? • How long insensitive and across which surface? • Demonstrate proper operation in harsh environment (fwd region of present LHC)

9. 5. Frontend electronics • Threshold should be increased because of threshold dispersion • Operating at threshold of 350 e- (= 5 x 70 e-) is not realistic • => need ≥ 5 times higher threshold • Why less power consumption? • Readout • How to handle the 3 – 10x larger data volume

10. 6. Photolithography • InGrid technology • Processing temperature? • Which companies are able to produce it? • On wafer scale? • Testing? • Yield? • Imperfections? • How far advanced? • Processing a 50 µm thick wafer? • Maximum thickness? • Any stresses? • TwinGrid • Is gain of TwinGrid the multiplication of the gains of each of the grids? • TwinGrid yield?

11. 7. Miscellaneous • Grid capacity of 100 nF? • Typo => InGrid of 15 x 15 mm2 has ~40 pF capacity • Thinning • How to do thinning in practise? • (I think: thin chips with handle on CMOS side, put handle on back-side, make InGrid, add gasCap, release handle?)

12. 8. Organization of the Gossip R&D • Collaboration • Present sharing of workload and costs? • Resources to prototype full wafers? • Define path cq milestones (with dates) leading to the production of a few demonstrators • To become a serious option for an application in ATLAS at the sLHC

13. Answers to the questions

14. Fig. . The spatial resolution X – X0 vs agle of incidence φ for different (square) pixel pitches, assuming a perfect time measurement. 1. Working point InGrid  -550V • Grid voltage • Depends on the gas mixture • - 400 – 450 V for mixtures with a large content of inert gases (He/iC4H10 80/20, Ar/CH2 90/10, ....) • - 550 - 600 V for a very slow gas like DME/CO2 50/50 (present favourite) • Width drift gap • 1.0 – 1.2 mm, depending on the ionization of the applied gas mixture and the required efficiency • Example: DME/CO2 50/50 • Efficiency on any ionization from a MIP for a drift gap of 1.0 mm => 98.9% • Cell size • Simulations have shown that a smaller cell sizes gives better resolution • 60 x 60 µm possible for 130 nm technology • Estimate for Gossipo-4 chip 0V 100 - 700 V/mm 50 µm Amplification gap 10 kV/mm Pixel chip

15. 1. Working point (cntd)gas mixture Not Gossip but GridPix with 19.3 mm drift gap CO2/DME 50/50 • Our favourite is presently DME/CO2 50/50 • Low diffusion (70 – 100 µm/√cm) • Low Lorentz angle (9º @ 2T) • Good cluster density (45 cl/cm) • 125 electrons/cm Ar/iC4H10 80/20 (June 2009 testbeam) Testbeam September 2009 Limited (38%) single e- eff. 80 pixels (4.4 mm) 80 pixels (4.4 mm)

16. 1. Working point (cntd)gas mixture • DME/CO2 is a very “viscous” gas for electrons • Vd ≈ 50 µm/ns @ E = 6 kV/cm Gossip working point

17. 1. Working point (cntd)Shaping time • Aim • making peaking time half the ionic drift time • Gossipo-2: peaking time 30 ns • Gossipo-3: will be reduced to 25 ns • Shaping time • ~ 30 ns for delta pulse • ~ 70 ns for detector signal • More details in the ASIC session Simulation Gossipo-2 Gossip pulse delta pulse 7500 e-

18. 2. Possible target regions for Gossip and GridPixsLHCfluences

19. 2. Possible target regions for Gossip and GridPixHigh rate pixel layers at the sLHC (R = 37 mm, b-layer) Motivation • Outlook for constant charge signal over the full lifetime at the sLHC • Without retuning grid voltage • Less material for the full structure including services and support than for most other technologies [ref. slide 37] • Hard to quantify at this stage of development, but substantial reduction of X/X0 expected • Absence of detection material (only gas) • No bump bonds • Relaxed cooling requirements Requirements • Radiative dose: until 2*1016 neq/cm2 => 3.4*1016 hadrons/cm2(mostly pions) • Rate up to 900 MHz/cm2 charged particles • Background of • ~ 200 MHz/cm2 neutrons • Gammas, alfas, slow electrons .....

20. 2. Possible target regions for Gossip and GridPixintermediate region (R ≈ 400 - 600 mm) “Outer GridPix detector with 50% of silicon material?” Motivation • Rather cheap coverage with high granularity layer • Mass expected to be lower than using silicon But less advantage than in the hot parts of Atlas Silicon has here • less dense RO • less generated heat • less dense services Requirements • Radiative dose: ~1014 hadrons/cm2 (mostly pions) • Rate up to ~3 MHz/cm2 charged particles • Background of • ~10 MHz/cm2 neutrons • Gammas, alfas, slow electrons .....

21. 2. Possible target regions for Gossip and GridPixGridPix as a L1 trigger • R = 850 -1150 mm • Drift gap ~ 16 mm • Using “regular” gas mixture for drift chambers (not DME/CO2) Motivation • Using ID tracker info for sharper L1 trigger Requirements • Radiative dose: ~ 3*1013 hadrons/cm2 • mostly pions • Rate ~ 1 MHz/cm2 charged particles • Background of • ~7 MHz/cm2 neutrons • Gammas, alfas, slow electrons .....

22. 2. Possible target regions for Gossip and GridPixGridPix as TRT • Like L1 trigger layers • R = 850 -1150 mm • Drift gap ~ 16 mm • Using Xe based mixture Motivation • e/p separation • Investigated in 2008 test beam • 90% electron efficiency with 2% false pions achievable using two layers Requirements • Radiative dose: ~ 3*1013 hadrons/cm2 • mostly pions • Rate ~ 1 MHz/cm2 charged particles • Background of • ~7 MHz/cm2 neutrons • Gammas, alfas, slow electrons ..... Fig. . Measured pion rejection power for two detector layers using the cluster counting method.

23. 3. Performanceageing • No ageing of the detection medium (chamber gas) • Ageing of the construction materials • Not incorporated in Gossip research (not Gossip specific) • Metals, ceramics, glass can (reasonably) sustain 2*1016 neq/cm2 (950 Mrad) • Also some plastics (PEEK) are OK • For Gossip R&D we presently focus on ageing by gas avalanche • => figure of merit is collected charge, NOT accumulated dose • Ageing in the form of a continuous or grainy deposit, disturbing the avalanche field • => smaller charge signals, broader signal distribution • Accelerated ageing (3 – 4 orders of magnitude possible) may be induced by minor concentrations (ppM – ppB level) of certain (organic) pollutants • Can be avoided by careful gas handling • Avoiding suspicious (most) plastics • Constructing detectors from safe materials • Not using glues (Araldite) but metals, ceramics, glass • Using appropriate filters (molecular sieves) • Note: • Ageing by gas avalanche only proceeds under grid voltage • => no ageing during beam fill, tuning, machine development A. Romaniuk et al, Nucl. Instr. and Meth. A515(2003)166

24. 3. Performance ageing (cntd) Fluence on the b-layer at sLHC in phase II • Dose@R = 37 mm • At b-layer radiative dose is dominated by direct tracks • Assume 3000 fb-1 data * safety factor 2 * 79 mb  pp Xsec * 6.3 tracks/ /interaction • 3*1017 tracks/ (mostly pions)‏ • At R = 37 mm, 1 cm is 0.269 units of  and 0.268 units of f out of 2 •  at R = 37 mm we get 3.4*1016 charged particles/cm2 • (Damage factor ~0.6 for pions 2.0*1016 neq/cm2 relevant for Si)‏ • Rate • 0.9 GHz/cm2 for 25ns sLHC • Corresponds to 9.5 * 106 Gy (950 Mrad) • Data from Atlas experts (Craig Buttar, Ian Dawson and Nigel Hessey)

25. 3. Performanceageing (cntd)Target dose values for Gossip radiation tolerance • Expressing dose as charge per cm2 (rather than neq/cm2) • Assume • Gas gain = 5000 • 12.6 e- average ionization across 1.0 mm (DME/CO2 50/50) •  1 MIP => 10 fC •  sLHC BL dose of 3.4*1016 MIPs/cm2 translates into 342 C/cm2 • Comparison to numbers for wire chambers • Assume sense wire Ø 20 µm • 342 C/cm2 ↔ 2.1 C/cm Fair number for wire chambers Well possible if outgassing elements are avoided

26. Performanceageing (cntd) • Example: wire chamber ageing • Obtaining 2.1 C/cm well possible R. Openshaw et al, Tests of wire chamber ageing with CF4/isobutane (80:20), argon/ethane (50:50) and argon/ethane/CF4 (48:48:4), IEEE Transactions on Nuclear Science, Vol. 36, No. 1, February 1989

27. 3. Performanceageing (how to study) • Target for b-layer at sLHC • 2*1016 neq/cm2 => 3.4*1016 cm-2charged hadrons (mostly pions) • Ageing studies harder than for solid state detectors because of the rate limitations of the avalanche process • Gossip will not operate at 100 – 1000 x increased sLHC rate • X-rays (like from GIF++) cannot be used • Other ionization profile (large clusters instead of short MIP tracks) • Upgraded PS beam too intense • Present PS beam might be just OK, but we cannot claim continuously it for many months • Solution: dedicated MIP source (up to ~ 1.8 GHz/cm2) at Nikhef • In addition ageing tests at other particle sources (neutrons) have to be done as well

28. 3. Performanceageing (Nikhef facility) • Nikhef setup using powerful 90Sr source (5 GBq) • Tiny irradiated surface (< 1 cm2) • Emitting ~ 2 MeV bs (~MIPs) • MIP rate up to 1.8 GHz/cm2 • Tests time consuming • Up to 4.8 x 1015/month • ~ some 7 months for full b-layer lifetime

29. 3. Performanceageing (experimental results) • 16.1 C/cm2 obtained so far • Ar/iC4H10 70/30 • Non-clean gas system • Epoxies used (Araldite) • measurement terminated because of sparking • Tests with other mixtures showed rapid ageing • Goal: 342 C/cm2 Using dummy Gossip (glass substrate with pixel pattern)

30. 3. Performancerate behaviour limits • Target • Atlas b-layer at sLHC: 0.9 GHz/cm2 • Occupancy • Dead time ~ 50 ns (ionic drift) • => occupancy limit (50%) at 20 MHz/pixel • Assume • 55 x 55 µm2 pixels • 12.5 hits per track (only for high angle of incidence) • => rate limit reached at 53 GHz/cm2 • Ionic drift • Avalanche gap (nearly all ions collected by the grid) • Average current density 9 µA/cm2 • Assume 50 ns stay in the gap • => space charge of 0.45 pC/cm2 • => Induced counter field ~ 2.5 V/cm • Ref: amplification field ~ 100 kV/cm • => rate effect from ionic drift in avalanche gap may be neglected

31. 3. Performancerate behaviour limits (cntd) • Ionic drift (cntd) • Limit by ions in the drift gap that are NOT collected by the InGrid • Assume drift field 2 kV/cm • Ion mobility ~ 3 x 10-4 m2/V.s • => ions stay in 1 mm gap for ~ 16 µs • Assume G = 5000 and 12.5 primary e-/MIP • => 0.01 pC/MIP or 14.4 nC/cm2 for the full b-layer rate and if all ions would pass the drift volume • Only ~ 2% of the ions is passing the InGrid¥=> 288 pC/cm2 counter charge • => counter field due to ionic charge 32 V/cm => < 2% of field • Limitations by protective layer • Permit voltage drop of 10V across protective layer • => bulk resistivity should be 1.6 x 109 Ω.cm • For Si3N4 to be tuned by silicon dope ¥ M. Chefdeville, Charge transparancies and amplification properties of Integrated Micromegas detectors, 2nd RD51 Workshop, Nikhef, April 17, 2008

32. 3. Performancerate dependence (experimental result) • Measurement of induced DC current • Using Gossip with dummy ROC (aluminium pixel pattern on glass) • No InGrid but glued Micromegas • => gap > 50 µm • No protection layer yet • Done after some loss of gain due to rapid ageing (non-clean gas system) • MIP rate 1.6 GHz/cm2 • No sign of loss of gain until G = 900 • Sparking starting at G = 1000 • Protection layer probably would have extended the sparking limit • => reliable operation of Gossip at b-layer environment (G = 5000) not yet fully proven

33. 3. Performanceefficiency depends on • Primary ionization (cluster density) • Assume gas gap of 1 mm • From Poisson statistics e = 1 – e-cl, where cl is the average number of clusters in the drift gap • For DME/CO2 => 98.9% (4.5 clusters on average) • Charge signal distribution for single electron starts at zero • Never 100% single electron efficiency • Pólya distribution factor pdf >1 makes distribution narrower • Discriminator threshold and required overdrive • Accepted drift time error (k = pdf – 1)

34. 3. Performancedelta rays • Typical artefact of gaseous detectors • Do not exist in solid state detectors because of their short range • Affecting ~ 1 - 2% of the events • Deteriorate resolution for most gaseous detectors since they are averaged with the rest of the track • In Gossip most of them can be rejected in the track fitting using its high granularity • Using track info from other detectors Examples of data rays in test beam data of run Sept 2009 using DME/CO2 50/50. Gossip gas gap 1.5 mm 4 mm 2.8 mm

35. Fig. . Coordinate system and nomenclature of track parameters. The X-Y coordinate (X0, Y0) is given by the crossing point of the fitted track with the reference plane. 3. Performancehow to handle track segments • Track is fitted in the frontend electronics through reconstructed 3D hit points • Crossing point between the fitted track and the reference plane is determined • Output has format of crossing point in X-Y (fixed Z) + angles φ and θ • 4 parameters

36. 3. Performancecooling • “Required capacity compared to silicon?” • Exact number not to be given at present, but expected to be substantially lower, especially for the b-layer • Reasons • Less emitted frontend power including digital part (50% of silicon frontend??) • Negligible environmental heat load at room temperature • Sensor bias current (may be 1W/cm2 for silicon, zero for Gossip) • No risk on thermal runaway • Bigger temperature gradient across heat spreader permitted (running at + 20º C instead of -20º C) • No problem with CTE mismatch when running at room temperature • “Why dependence on operation temperature?” • Better heat transfer at higher cooling pipe temperature • => thinner cooling pipe

37. 3. Performancematerial budget (X/X0) • Double layer to provide 100% coverage • Dominated by services and support (78%) • ~50% of that of silicon (2.5 – 3%) because of • Much less cooling material • Massless detecting medium • Less material in LV cables

38. 3. PerformanceExperimental results from testbeam September 2009 • Using T10 at PS • 6 GeV pions, low duty cycle • Detectors built using TimePix chip • 55 x 55 µm2 cell size; TDC running at 80 MHz • Using DME/CO2 for the first time, not tested beforehand • Beam entering under ~ 12º • Gossip 1 => excellent SE efficiency (close to 100%) • Gossip 2 => not working • Gossip 3 => very poor SE efficiency (~16%) • GridPix (DICE) => poor SE efficiency (~ 38%)

39. 3. Performancedata analysis testbeam September 2009 DICE • Noisy events rejected (discharges) • Noisy pixels masked (1 – 2%, mostly at the edges) • DICE (GridPix detector) used as reference • Tracks found in DICE were traced backwards in Gossip 3 and Gossip 1 • Edge zones rejected • Field lines bend because of bad field shaping 4 mm 2.8 mm

40. 3. Performanceangular resolution • Detector Gossip 1 • 1.5 mm drift gap • Single hit events excluded • X – Z plane • slope 4.1 mrad (0.23⁰) • Resolution 15 mrad (0.9⁰) in X • Good for 1.5 mm of gas • Y – Z plane • Y – Z plane: slope 220 mrad (12.6⁰) • Resolution 70 mrad (4⁰) in Y • Deteriorated by discriminator delay • Note the asymmetric distribution • => long erroneous drift time make angle smaller

41. 3. Performance Measuring position resolution Draw straight line between master points in Gossip 1 and DICE • Calculate the master point in Gossip 3 as the simple average of all the pixel hits in X, Y and Z • Calculate the distance between the straight line and the Gossip 3 master point Gossip 3

42. 3. Performanceposition resolution • Limited statistcs: 75 events • 40% track efficiency in Gossip 3 • Residuals in X: σ = 30 - 35 µm • This number includes • Accuracy of the fitted track (10 µm?) • Multiple scattering in 6 GeV beam (10 – 30 µm) • Poor hit statistics • average 1.5 hit pixels instead of 4.5 expected • => σ ≈ 15 µm expected for well operating Gossip • Residuals in Y: σ = 70 - 80 µm • => same correction: σ ≈ 45 µm expected for well operating Gossip • Time info used for all three detectors • Worse result if you don’t use it

43. 3. PerformanceTrack efficiency • Method • tracing tracks in Gossip1 that were found in DICE (GridPix reference detector) • At least one hit in Gossip 1 required • Good track efficiency of Gossip 1 (1.5 mm gap) • 99.5% • But in hit spectrum 1 single-hit event and 5 two-hit events • => if we would use a 1 mm drift gap instead, we would miss on the average: • 1/3 event from 1 event with one hit • 5/9 event from 5 events with two hits • => based on this measurement expected efficiency for 1 mm gap: ~99.1% • But beware of limited statistics (197 events) • Expected from known cluster density for 1 mm gap 98.9%

44. 3. Performancenumber of hits per track Gossip 1 • Method • tracing tracks in Gossip1 that were found in DICE (GridPix reference detector • Tracks entering under 12º • Measurement • MIP through DME/CO2 gives on average 18.8 electrons per track • => naively expected 18.8 hits/track (one hit per electron) • Measured 6.7 hits/track • Caused by pile up • 1 pixel is hit by several electrons • Projection length surface: 0.21 mm • => less than 4 pixel cells

45. 4. Sparkingorigin • Occasional sparking is normal for each gaseous detector (exceeding Raether limit) • At the Landau tail • Alfas • Ions; converting neutrons; gammas • Most probable Gossip charge signal at working point: 62 ke- • Sparking limit for G=5000: 300 ke- • ~ 5 x most probable charge signal • There are indications that a protection layer extends this limit • Still to be investigated using high rate MIP source at Nikhef Gossip working point (b-layer)

46. 4. Sparkinghow to survive sparks InGrid Si3N4 • Limit the energy of the spark • Reducing the capacity of InGrid • High supply resistor and • Small or no decoupling capacitor • InGrid capacity 40 pF for 15 x 15 mm • Adding protection layer • => acts as small coupling capacitance in the input circuit • => Spark energy is distributed across multitude of pixels • Limit the peak current in case of a discharge • Adding resistivity in the discharge circuit (resistive InGrid) • Incorporate input protection (diodes) in the frontend ASIC Pixel chip Functioning protection layer Surface part near discharge is charged up Discharge cannot sustain itself and jumps to neighbouring cell Discharge process continues until grid potential is sufficiently small

47. 4. SparkingHV connections • Spark protection by external HV circuitry Limiting discharge current Filtering HV Component values only indicative Cathode Vcath 100 M 100 M Gossip/GridPix InGrid Vgrid 10 M 10 M 10 n 10 n 0-30 p 0-100 p GND Pixel chip

48. α tracks having high primary ionisation  exceeding Raether limit of 108 e- in the avalanche 4. Sparkingtesting using alfas • Limiting the discharge current. • Reduce amount of charge. • Spread the charge. Pixelman software: IEAP, Prague

49. 4. Sparkingvarious questions • “Demonstration for large system” • Should be done • “Sparking rate?” • Particle rate dependent, to be investigated • “How long insensitive and across which surface?” • Also to be investigated • Wild guess: • Small discharges: insensitive during few µs and across ~ 1 mm • Large discharges: insensitive during ~ 1 ms and across full InGrid • “Demonstrate proper operation in harsh environment (fwd region of present LHC)” • Test like this is crucial after successful tests at the Nikhef facility

50. 5. Frontend electronics • “Threshold should be increased because of threshold dispersion” • Present Gossipo chips have a threshold trim DAC for each channel • “Operating threshold of 350 e- is not realistic, need 5x higher threshold” • Gossipo-2 (pixel chip with 16 x 16 matrix) operates on 350 e- • ASIC designers estimate a threshold of 500 e- a workable value for a big system • Still to be tried out • note very low detector capacity • “Why less power consumption?” • Absence of bias current and negligible input capacity enable a low current in the input stage • Preamp Gossipo-2 => 2 µW • Ref.: FE-I4: 10 µW • Limited contribution of digital electronics (0.4 µW) • Note: local track fitting processor not yet implemented Gossipo-2 chip