1. (non-)Destructive high-rate tests on silicon strip modules Emulating LHC beam incidents using the PS booster and measuring the effect on a LHCb Velo silicon strip module Lars Eklund, on the behalf of the LHCb Collaboration

2. 14 September, 2009 L. Eklund, Vertex 2009 2 Outline Introduction –Motivation and previous publications The participants –The PS booster and the LHCb/VELO module The measurements –Observables and program The surprise –Results and interpretations Summary

3. 14 September, 2009 L. Eklund, Vertex 2009 3 Motivation (1) The LHC Stored beam energy 10 2 - 10 3 times larger than any previous accelerator New machine, limited operational experience The LHCb Velo Very close to the beam: silicon sensors @ 7-30 mm distance (moving!) Located next to the injection line TI8 Designed and built: but operation procedures can be changed –LV & HV on/off at injection? Feedback to the machine –Intensity limit at injection –Currently H/W 10 11 protons and F/W 10 10

4. 14 September, 2009 L. Eklund, Vertex 2009 4 Motivation (2) Possible beam incidents Injection failures: –incomplete or unsynchronized kicker fire=> mostly Alice & LHCb –wrong magnet settings in transfer line=> mostly Alice & LHCb –wrong magnet settings in the LHC=> everybody Circulating beam failures: (mostly caught by collimators) –magnet failure / mishap=> everybody –RF failure=> everybody –collimator failure / mishap=> everybody Extraction failures: –Under-kick, unsynchronized beam dump=> mostly CMS

5. 14 September, 2009 L. Eklund, Vertex 2009 5 Previous studies Atlas silicon strip sensors: LASER (2 types) –IEEE Trans. Nucl. Sci. NS47 (2000) 1902 –Voltage across AC coupling vs. R RC &C RC Atlas silicon strip: 1064 nm LASER (1 W) –NIM A 541 (2005) 15-20 –Beam spot 8 µm, 10 ns pulse, 10 9 MIP equivalent –Damage: HV bias > 200 V @ 10 9 MIP (on one strip) CMS silicon strip: 24 GeV protons (CERN/PS) –NIM A 518 (2004) 328-330 –Beam spot 10x3 cm 2, 42 ns bunch, 2 bunches of 7x10 10 protons –No damage Atlas pixel: 24 GeV protons (CERN/PS) –NIM A 565 (2006) 50 –Beam spot 6x3 cm 2, 42 ns bunch, 8 bunches of 1x10 11 protons –No damage

6. 14 September, 2009 L. Eklund, Vertex 2009 6 The PS booster Resto 2 Mainbldg

7. 14 September, 2009 L. Eklund, Vertex 2009 7 The beam line Proton beam with 1.4 GeV energy Intensity: 2x10 9 – 9x10 12 p Beam spot: 5 mm (max 4x10 13 p/cm 2 ) Bunch length: ~200 ns Cf. tests in the PS: max 3x10 10 p/cm 2 Compare with LHC Pilot bunch @ injection: 2x10 9 protons (450 GeV) –300 µm beam spot –0.4 ns bunch length Full luminosity (L=10 34 ) SPS injection train –288 bunches of 10 11 protons –4x10 13 protons/cm 2 /bunch

8. 14 September, 2009 L. Eklund, Vertex 2009 8 The set-up Module mounted close to the beam dump –Back-splash gives non-negligible dose –Rough estimate of dose: 10 13 n eq & 1 kGy (very preliminary) Small scale experiment

9. 14 September, 2009 L. Eklund, Vertex 2009 9 The victim LHCb/Velo spare from production Double sided (R & Phi sensors) 2048 AC coupled n-on-n strips / side 16 FE chips (IBM 0.25 µm) Mounted in the beam line Cooled to +1 ˚C (LV on) Florescent screen to view the beam Insert/retract from beam line Remote control and read-out

10. Electrical model – static case Al SiO 2 n p+ n+ C DET R DET C AC R bias C RC Q RC C RC R RC HV bias (-300V) HV return (GND) Q RC RC filter GND bonds (16x5) pre-amp C FB V fp CGCG protection diodes bond wires FE inputs (2048 channels) V DD bonds (16x4) LV (GND) LV (V DD ) C LV C DET = 1 nF/2048 ch. R DET = 1-100 MΩ/2048 ch. C AC = 250 nF/2048 ch. R bias = 1 kΩ x 2048 ch. C RC = 10 nF R RC = 5 kΩ C FB = 400 fF (per ch.) C G = 10 pF (per ch.) C LV = 32 x 100nF 10 MΩ GND probe HV probe Osc. GND 22 nF 1 kΩ 10 MΩ 10 pF

11. 14 September, 2009 L. Eklund, Vertex 2009 11 The measurement sequence - observables Intensity steps: 2x10 9, 2x10 10, 2x10 11, 2x10 12 & 9x10 12 Each step: LV/HV off, LV on/HV off, LV on/HV 150 V & LV on/HV 300V Each beam ‘shot’ follows the same pattern –A set of standard measurements I/V of both sensors Noise & pedestal data Test pulse data at +1.5, 0 and -150 V (for some shots) –Insert the module, acquire during the shot 14 consecutive triggers of front-end data Voltage on hybrid GND and sensor bias via oscilloscope Beam spot image via a a camera –Repeat the same set of measurements Shots on two sensor positions Shots on five front-end chips (only LV on/off matters) No measurable damage up to 9x1012 @ 300V bias on the sensor 2x1011 (LV on) on the FE chips

12. 14 September, 2009 L. Eklund, Vertex 2009 12 Beam images Beam line camera on scintillating screen Combined R-Φ sensor front-end data

13. 14 September, 2009 L. Eklund, Vertex 2009 13 I/V curves I/V curves in-situ between each shot –Superimpose temperature corrected I/V curves –Small increase probably due to accumulated dose –Rough estimate between first and last curve: 3x10 12 n eq & 200 Gy Work in progress –Correlate with radiation monitoring data

14. 14 September, 2009 L. Eklund, Vertex 2009 14 Thermal image: No hot-spots The majority of the shots hit this area

15. 14 September, 2009 L. Eklund, Vertex 2009 15 Noise & Pedestals Noise & pedestals measured in-situ between each shot –Plots show date taken towards the end of the program –No change visible Detailed analysis is in progress

16. 14 September, 2009 L. Eklund, Vertex 2009 16 Test pulse response – post-zap Test pulse response – ‘booster’: in-situ after a few shots at 2x10 9 – ‘lab’: lab measurement after the full program Gain difference due to different analogue drivers/receivers Bad channels identical to production QA

17. 14 September, 2009 L. Eklund, Vertex 2009 17 Post-mortem – why did it survive? Deposited energy (in 300 µm Si) –9x10 12 x 24 k MIPs x 3.6 eV = 1.2 Joule / 200 ns –Temperature increase in 1 cm 2 Si: 2.5 ˚C –Maximum SPS injection train (288x10 11 ): 4 Joule / 10 µs Local energy store: the RC filter –10 nF @ 300V => 0.5 mJ –Absorption volume critical Massive ionisation in biased silicon –Q RC (300V) = 3 µC –Deposited charge @ 2x10 9 : 7.5 µC Possible transient damage –Current through front-end –AC coupling diode –Voltage on front-end input –Fast HV ramp-down vivum HV bias reduced to 0 V

18. 14 September, 2009 L. Eklund, Vertex 2009 18 Voltage across the sensor vs. time Oscilloscope measurements –Hybrid GND –Backplane –1 sample / ns Ground reference arbitrary –Huge ground bounce –Large pick-up –Plot V backplane -V hybridGND Two distinct features –Sharp rising edge (50 ns) –Slow charge-up time [µs]

19. 14 September, 2009 L. Eklund, Vertex 2009 19 time [µs] The first 50 ns … 6 GV/s 2 GV/s 2.5 GV/s

20. 14 September, 2009 L. Eklund, Vertex 2009 20 Electrical model – the first 50 ns … Al SiO 2 n p+ n+ C DET IZIZ C AC R bias C RC = 10 nF Q RC = 3 µC R RC RC filter GND bonds (16x5) pre-amp CGCG protection diodes bond wires FE inputs (2048 channels) V DD bonds (16x4) C LV I Z /2048 V AC I GND = I Z /80 V IN IZIZ R IN Current during the discharge Divided between 2048 inputs and 80 GND bonds Q RC transferred to C AC V IN = I Z /N x R IN N is large (~ 2048) R IN is small (~Ωs) Ramping 300 to 0 V in 50 ns seems to be OK! R bias reduced to ~100kΩ/2048 via punch-through mechanism Still to large to play a role

21. 14 September, 2009 L. Eklund, Vertex 2009 21 Shots on the FE chips 56 shots on the FE chips: 2x10 9 – 2x10 11 No destructive latch-up –Design rules include structures to prevent latch-up –Seems to be effective! SEU analysis in progress: none observed so far –Requires large energy deposited in small volume –Nuclear reactions necessary –Cross-section very low –Triple-redundant registers: corrected every 2 ns

22. 14 September, 2009 L. Eklund, Vertex 2009 22 Summary The PS booster provided beam to emulate LHC beam incidents –200 ns shots, 2x10 9 to 9*10 12 protons A VELO strip module was subject to a large number of shots –Two positions on the sensor, five FE chips Survived 9x10 12 protons on sensor with 300 V bias Survived 2x10 11 protons on the FE chip No visible change in performance –I/V curves, noise, pedestals, thermal imaging, … Saving graces –The whole sensor responds as a unit –Large area sensor – many channels –C AC >> C RC (+C DET ) –Protection diodes on the FE inputs –Triple-redundant registers in FE chips Analysis & measurement still in progress

23. 14 September, 2009 L. Eklund, Vertex 2009 23 Back-up slides

24. 14 September, 2009 L. Eklund, Vertex 2009 24 Total number of shots Intensity LV off HV off LV on HV off LV on HV 150V LV on HV 300V 2*10 9 1229+32 2*10 10 1111 2*10 11 1111 2*10 12 1111 9*10 12 2255 Shots on the sensor (position 1+2) Intensity Beetle 4Beetle 5Beetle 6Beetle 7 LV onLV offLV onLV offLV onLV offLV onLV off 2*10 9 --243336 2*10 10 33533366 2*10 11 -3------ Shots on the front-end chips B2 B6 B0 B3 B4 B7 B5 B1 63 shots on the sensor 56 shots on the FE chips

25. 14 September, 2009 L. Eklund, Vertex 2009 25 Beam size – seen by the Φ-sensor “FWHM” of beam ~80 strips of 70  m pitch ~5.5 mm Response to beam during initial 25 ns of beam rising edge in  detector

26. 14 September, 2009 L. Eklund, Vertex 2009 26 Fitting rising edge of all shots Termination of HV monitoring signal was improved during the program Rising edge not affected by termination 150 V: Shots 3-5 & 24 @ 2e9, shot 10 @ 2e10 and shot 14 @ 2e11 are less than 1 GV/s 300V & 9e12: Shots 34, 42, 44 are greater than 5 GV/s Weak correlation with intensity & voltage Large shot-to-shot variation

27. 14 September, 2009 L. Eklund, Vertex 2009 27 Re-charge of HV … Average time constants –τ = 6.8 μs @ 2e9 & 150V –τ = 13 μs @ 9e12 & 150V –τ = 10 μs @ 9e12 & 300V Need spice simulation to understand recovery times Re-charge depend on intensity –Some long term (10μs) process in the sensor?

28. 14 September, 2009 L. Eklund, Vertex 2009 28 Decay-time of all available wave forms Falling edge clearly affected by the termination Not possible to compare the two data-sets De-convolution of impulse response maybe possible