1. Zerguerras T. – IPNO – RDD – 14/06/2013 RD51 Collaboration Meeting July, Zaragoza 5-6th 2013 1/12 New results on gas gain fluctuations in a Micromegas detector Unité mixte de recherche CNRS-IN2P3 Université Paris-Sud 91406 Orsay cedex Tél. : +33 1 69 15 73 40 Fax : +33 1 69 15 64 70 http://ipnweb.in2p3.fr T. Zerguerras, B. Genolini, M. Imré, M. Josselin, A. Maroni, T. Nguyen Trung, J. Pouthas, E. Rindel, P. Rosier, L. Séminor, D. Suzuki, C. Théneau

2. Zerguerras T. – IPNO – RDD – 14/06/2013 2/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 A Laser test bench for MPGD study - MPGD characterization with a point-like electron source ( <100 µm) of variable intensity produced by a 337nm UV laser. - Study performed with a prototype for the ACTAR (ACTive TARget) project Laser Conversion gap (1.6 mm) Amplification gap (160 µm) X Photon Quartz lamina with a 0.5nm-thick Ni-Cr layer Micromegas Ni mesh Anode Micromegas PMT Laser optics Optical fiber Energy resolution following the number of primary electrons N 0 a :laser intrinsic constant F las : N 0 fluctuations from f and ( f + F las ) Single Electron Response Relative gain variance : f = 0.30 ± 0.01 Gain= 6.0 10 4 0 e - 1 e - 1) 2) Electronic: Gassiplex (2 000 e - rms) T. Zerguerras et al., NIM A 608 (2009) 397 Ne 95% iC4H10 5%

3. Zerguerras T. – IPNO – RDD – 14/06/2013 3/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Improvements in 2013 Simplified geometry : - Complex anode pad plane geometry - Position of the 55 Fe source Lower noise level: - Lower limit of gain at ~ 3. 10 4 for SER measurements - Only for high-gain gas mixtures (ex: Ne:iC 4 H 10 95:5) Redesigned detector Simplification of the anode plane segmentation Change Front-End Electronics Adapt the electronics chain Lower pressure: Pressure regulation and control system for studies at lower pressure. 2009 2013 2009 2013

4. Zerguerras T. – IPNO – RDD – 14/06/2013 4/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Detector improved Conversion gap: 3,2mm Amplification gap: 160µm Mesh: Buckbee Myers © 333 lpi nickel electroformed micromesh 5mm 10mm Anode: 3 pads Change of the mechanics and simplification of the anode pad plane geometry Improvement of electronics S/N ratio Cremat CR-110 PAC Gain: 1.4V/pC Noise : 200 e - RMS (table) 380 e - RMS (detector) + CAEN N568B Spectroscopy Amplifier (CG, FG fixed, SH=3µs, PZ fixed, Offset fixed) Pressure control system Calibration through a high-precision 1pF capacitance at the channel test-input

5. Zerguerras T. – IPNO – RDD – 14/06/2013 5/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Measurement with a 55 Fe source Ar 95% iC 4 H 10 5%, 750 torrs, V d = 738V V mesh = 450V, CG 5 FWHM @5.9keV: 21% Ne 95% iC 4 H 10 5%, 750 torrs, V d = 718V V mesh = 430V, CG 2 FWHM @5.9keV: 14%

6. Zerguerras T. – IPNO – RDD – 14/06/2013 6/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Method for Single-Electron Response (SER) measurement - The laser is focused on the drift electrode in front of the central pad - A light-attenuator of factor 100 is put at the output of the laser box. Trigger: XP2282B anode signal - Trigger: XP2282B anode signal Proportion of non-zero events (outside pedestal) is < 5% - Proportion of non-zero events (outside pedestal) is < 5% - The anode charge is measured to monitor the laser light intensity (variation < 4%) The CG of the N568B Spectroscopy Amplifier is adjusted depending on - The CG of the N568B Spectroscopy Amplifier is adjusted depending on the mesh voltage, all the other parameters being fixed the mesh voltage, all the other parameters being fixed -The drift field is of 900V/cm -Gas mixtures: Ar 95% iC 4 H 10 5%, Ne 95% iC 4 H 10 5%, He 95% iC 4 H 10 5% @ 750 torrs @ 750 torrs -To avoid any damage on the CR-110 chips, the maximum voltage applied on the mesh was 10V below the sparking limit voltage

7. Zerguerras T. – IPNO – RDD – 14/06/2013 7/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Single-Electron Response Gain < 10 4 G = 5.5 10 3  = 0.8 ± 0.1 f = 0.56 ± 0.03 Ar 95% iC 4 H 10 5%, V mesh =450V, CG 7 G = 5.4 10 3  = 2.0 ± 0.1 f = 0.33 ± 0.01 Ne 95% iC 4 H 10 5%, V mesh = 390V, CG 6 He 95% iC 4 H 10 5%, V mesh = 420V, CG 7 G = 5.7 10 3  = 1.7 ± 0.3 f = 0.37 ± 0.03 Gain: G Relative gain variance: f =1/1+  Sum of a Polya distribution: and a Gaussian (pedestal) fitted on data

8. Zerguerras T. – IPNO – RDD – 14/06/2013 8/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Single-Electron Response 10 4 < Gain < 10 5 10 4 < Gain < 10 5 G = 5.9 10 4  = 2.0 ± 0.1 f = 0.33 ± 0.01 Ne 95% iC 4 H 10 5%, V mesh = 470V, CG 4 Ar 95% iC 4 H 10 5%, V mesh = 490V, CG 6 G = 2.0 10 4  = 0.7 ± 0.1 f = 0.59 ± 0.03 Polya distribution fitted on data Gain: G Relative gain variance: f =1/1+  G = 5.3 10 4  = 1.9 ± 0.2 f = 0.34 ± 0.02 He 95% iC 4 H 10 5%, V mesh = 500V, CG 4 Maximum achievable gain before sparking

9. Zerguerras T. – IPNO – RDD – 14/06/2013 9/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Single-Electron Response Gain > 10 5 Gain > 10 5 G = 2.6 10 5  = 1.7 ± 0.1 f = 0.37 ± 0.01 Ne 95% iC 4 H 10 5%, V mesh = 520V, CG 2 G = 2.1 10 5  = 1.6 ± 0.2 f = 0.38 ± 0.03 He 95% iC 4 H 10 5%, V mesh = 550V, CG 2 Maximum achievable gain for both gas mixtures.

10. Zerguerras T. – IPNO – RDD – 14/06/2013 10/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Gain comparison The maximum achievable gain is 10 times higher in Ne 95% iC 4 H 10 5% than in Ar 95% iC 4 H 10 5%. For a given mesh voltage, the gain is about 7 (resp. 2) times higher in Ne 95% iC 4 H 10 5% than in Ar 95% iC 4 H 10 5% (resp. He 95% iC 4 H 10 5% ).

11. Zerguerras T. – IPNO – RDD – 14/06/2013 11/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Relative gain variances -In the measurement range, the relative gain variance f is rather independent of the gain. -For the same gain value, f is almost twice higher in Ar 95% iC 4 H 10 5% than in the two other mixtures. -As a consequence of their higher ionization yields, lighter gases have a lower value of f H. Schindler, S.F. Biagi and R. Veenhof, NIM A 624 (2010) 78-84 (H. Schindler, S.F. Biagi and R. Veenhof, NIM A 624 (2010) 78-84). - In the present study, gas mixtures with lower relative gain variance have higher sparking limits. Lower limit of 2009 study: ~ 3.7 10 4

12. Zerguerras T. – IPNO – RDD – 14/06/2013 12/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Conclusions Single-Electron Response (SER) can be measured After the test-bench improvements, Single-Electron Response (SER) can be measured down to gains of ~ 5.10 3 Relative gain variances of three binary gas mixtures (Ar, Ne, He + 5% iC 4 H 10 @ 750 torrs ) are deduced from the SER of a Micromegas detector. the relative gain variance is almost twice higher in the Ar-based mixture For a given gain, the relative gain variance is almost twice higher in the Ar-based mixture The maximum achievable gain in the Ar-based mixture (~2. 10 4 ) is ten times lower than in the Ne and He-based mixtures Comparisons with calculations are needed Comparisons with calculations are needed (discussion with WG4) and could help quantifying Penning effect in the three tested mixtures. Other parameters are worth of interest for further measurements Other parameters are worth of interest for further measurements: nature and proportion of quencher, pressure, type of mesh, amplification gap thickness …

13. Zerguerras T. – IPNO – RDD – 14/06/2013 13/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Backup Slides

14. Zerguerras T. – IPNO – RDD – 14/06/2013 14/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Relative gain variance calculations H. Schindler, S.F. Biagi and R. Veenhof, NIM A 624 (2010) 78.

15. Zerguerras T. – IPNO – RDD – 14/06/2013 15/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Ionization yield calculations for pure rare gases H. Schindler, S.F. Biagi and R. Veenhof, NIM A 624 (2010) 78.

16. Zerguerras T. – IPNO – RDD – 14/06/2013 16/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Neon Electron scattering cross-sections Argon H. Schindler, S.F. Biagi and R. Veenhof, NIM A 624 (2010) 78.

17. Zerguerras T. – IPNO – RDD – 14/06/2013 17/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Log(G)= d/ x exp(-I e / E amp ) Ne 95% iC 4 H 10 5% :  = 4.22 +/- 0.03 µm I e = 15.3 +/- 0.1 eV Pure Neon: I e = 21.6eV Ar 95% iC 4 H 10 5% :  = 3.24 +/- 0.15 µm I e = 16.0 +/- 1.2 eV Pure Ar: I e = 15.8eV d: amplification gap  electron mean-free path  I e : energy ionisation threshold E amp : amplification field F.J. Iguaz et al., 2012 JINST 7 P04007 following F.J. Iguaz et al., 2012 JINST 7 P04007 He 95% iC 4 H 10 5% :  = 4.16 +/- 0.04 µm I e = 16.4 +/- 0.3 eV Pure Helium: I e = 24.6eV Rose-Korff parameterisation

18. Zerguerras T. – IPNO – RDD – 14/06/2013 18/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Photon-absorption cross-sections O. Sahin et al., 2010 JINST 5 P05002

19. Zerguerras T. – IPNO – RDD – 14/06/2013 19/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Measurements @ different CG values G = 7.7 10 4  = 2.3 ± 0.1 f = 0.30 ± 0.01 Ne 95% iC 4 H 10 5%, V mesh = 480V, 750 torrs CG 2 CG 3 G = 7.3 10 4  = 2.2 ± 0.1 f = 0.31 ± 0.01 CG 4 G = 7.7 10 4  = 2.0 ± 0.1 f = 0.33 ± 0.01 CG 5 G = 8.1 10 4  = 2.2 ± 0.1 f = 0.31 ± 0.01

20. Zerguerras T. – IPNO – RDD – 14/06/2013 20/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 A pulse signal is injected on the test input of the central pad (Pad_C) through a 1pF capacitance Electronic chain calibration

21. Zerguerras T. – IPNO – RDD – 14/06/2013 21/12 RD51 Collaboration Meeting, Zaragoza, 5-6th July 2013 Electronic chain calibration