1. Summary of MM meeting at CEA Saclay, 25/26 Jan 2010 Some selected topics

2. CLAS12 and Compass Damien Neyret H4 (RD51) test beam run in fall 2009 in magnetic field Discharge studies (10 prototypes, different meshes) – Resistive layers, GEM foils pre-amplification – Charge spreading Preliminary results – compatible with old Compass studies (D. Thers et al.) – very small differences between classic MM and bulk – no impact of magnetic field on discharge rate so far – promising results from MM+GEM detector – further studies to be done: resist and MM+GEM with high and low intensity hadrons, performances with magnetic field, time resolutions

3. Damien Neyret, slide 8

5. Sebastien Procureur Simulation of the spark rate in a Micromegas detector with Geant4 Geant4 simulation of MM in hadron beams

6. Spark rate estimate and experiment Tool will be useful to optimize detector design Still some doubts about reliability of simulation at low energies Sabstien Procureur

7. Shuoxing Wu Analysis on November test beam Standard bulk detectors (2 M Ω/ ☐ ) Resistive Kapton: R3 & R4 (250 M Ω/ ☐ ) Resistive paste: R5 (400K Ω/ ☐ ) Resistive strips: R6 (Few tens of k Ω/ ☐ ) Resistive pads: R7 Segmented one: S1 Y Resistive Non-Resistive XYX X Beam 1 mm0.25 mm1 mm Detectors in test

8. Sparking behaviors of R6&S1: eight sparking six sparking five sparking four sparking three sparking two sparking one sparking S1: R6: 400K Ω/ Resistive strips (paste) 8 Shuoxing Wu

9. DetectortypeSpark rateSpark current /  A Voltage drop SLHC2 standard 7*E-50.45% R3 2 M Ω/ resistive kapton 9.6*E-60.22% R5 250 M Ω/ resistive paste 1.6*E-40.11.5% R6 400K Ω/ resistive strip 6.4*E-60.080.5% R7 tens of K Ω/ resistive pad 5.9*E-40.354.5% Detector performance at same gas gain (~3000)(preliminary): Shuoxing Wu

10. Conclusion and outlook: Resistive coating is a successful method to reduce the micromegas spark rate and limit the change in mesh voltage and current. Good spatial resolution<100  m can be reached with a resistive strip coating detector of 1mm pitch. High efficiency (>98%) can be achieved with resistive strip coating micromegas detector, and efficiency drops less than 4% when increasing the beam intensity from 5KHz to 40KHz. The definition of real ‘spark’ needs to be discussed. R&D and studies will continue inside the MAMMA collaboration (next beam test in 6 months) Shuoxing Wu

11. Topology of sparks: tests in the laboratory Esther Ferrer Ribas, Arnaud Giganon, Yannis Giomataris, Fabien Jeanneau 24th-25th January 2010, Spark working Meeting Saclay Compare in exactly the same conditions (same electronic chain) Amplitude of the spark (charge released) Dead time Esther Ferrer Ribas

12. Measuring sparks: The Chain R1 5.6 KΩ MM detector HT mesh R2 5.6 KΩ C = 470 pF C = 1.5 pF ORTEC 142B Am 241 Oscilloscope Esther Ferrer Ribas

13. Examples of pulses STANDARD RESISTIVE Esther Ferrer Ribas

14. Amplitude – charge considerations Standard case: the whole mesh is completely decharged Q tot = C det × V mesh C det = 600 pF, V mesh = 400 V N e = Q tot / q e = 24 × 10 4 pC/ q e ~ 1.5 × 10 12 N e ~ 1.5 × 10 12 With the measured pulses in the resistive case: V PA ~ 8 V, C= 1.5 pF Gain PA = 450 mV/pC N e ~ 2 × 10 10 To be continued In a systematic way and with all types of resistive detectors… Need a lower gain PA to avoid saturation in the standard pulses It seems that the released charge in a resistive detector is ~1000lower than in a standard one Dead time probably a high gain as well Careful analyis of the pulses is needed. Study and understand the different regimes < Esther Ferrer Ribas

15. Status of test beam data analysis … with emphasis on resistive coating studies Progress and questions 15Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN

16. R5  Similar to R3 but with more robust resistive layer and different technique (Rui’s talk)  R ≈ 5 kΩ Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN16 PCB Resistive paste Insulator ≈ 50 µm 1mm x 0.15 mm pad Mesh

17. R5 spectra Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN17 Gain = 5000 10000 S3 (570 V)

18. R5: first observations  First measurements of R5 ( 55 Fe source)  Sparking starts at HV mesh ≈ 560 V  Large currents (several µA)  Large HV drop (100–200 V)  R5 signal ≈2 x S3 signal  For comparison: R3 signal ≈ 0.8 x S3 signal  Charge resolution much worse than for S3 (and R3); escape peak not well separated Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN18

19. Two stages mMega Double mesh (Dmesh) or Gem as options for Preamplification gap

20. Gain vs. HV on the mMega and Gem Gain vs. HV on the mMega and Dmesh

21. Max. gain vs. HV Gem or D mesh for Fe55 and Alpha

22. 09/06/2009Rui De Oliveira22 Resistive protections Rui de oliveira

23. 09/06/2009Rui De Oliveira23

24. 09/06/2009Rui De Oliveira24 40um kapton >1kv breakdown voltage 1 mm resistor More than 1kv breakdown Voltage 5Kohms (Omegaply in future) Copper Strip 0.1mm x 100mm Pad : 150um x 1.5mm Microvia

25. 09/06/2009Rui De Oliveira25 R1 c2c3 GND -500V c1 Mesh Strip 0.1mm x 10cm Gas 130um PCB 3mm c4 C1 : 200pF ?Decoupling capacitor for readout C2 : in the range of 5pFParasitic capacitor mesh to strip C3 : in the range of 1.5pFParasitic capacitor strip to GND C4 : in the range of 1nFParasitic capacitor mesh to GND R1 : 1Mohms ?Resistor to discharge strip R2 : 10 Ohms ?Limiting resistor for spark current R3 0 ohms charge

26. 09/06/2009Rui De Oliveira26 R1 c2c3 GND -400V c1 -In normal operation the induced charge will be split between Z1 and Z2 -Maximum charge will flow through Z1 if Z1<<Z2 -Z2 = (C2 serial C4)//C3 we forget R1 which is high compared to the capacitors -Z2= C2//C3 because C2 serial C4 is close to C2 -C1 min should be 10 x C2//C3 : 10x 6.5pf  65pf min  200pf good choice -to capture the maximum of charge :Z1 should be as low as possible charge Z1 Z2 c4 0 ohms R3

27. 09/06/2009Rui De Oliveira27 R1 c2c3 GND -500V c1 -In spark mode the current will be mainly define by C4 and Z1 - Z1 at 1Ghz is: ZC1 + R3 -C1=200pF  3 Ohms at 1Ghz and 100 Ohms at 10Mhz -Peak current : 500V/13ohms = 39A during a few ns (170 A without R3) 500V/110 =4.5A during 100ns -the average current is in this case around 0.7uA (1.5uA without R3) -Up to 10 lines should be sparking at the same time looking at the currents measured sparkZ1 c4 0 ohms R3

28. 09/06/2009Rui De Oliveira28 c2c3 GND -400V c5 signal c4 0 ohms c6 -In normal operation the induced charge will be split between C5 and C6 (on both sides capacitors are virtually grounded) -C6 is in the range of 0.01pf and C5 0.1pf -R1 should be higher than C5 at any frequency but low enough to keep high rates (5K for test 3) Strip 0.1mm x 10cm pad R1

29. 09/06/2009Rui De Oliveira29 c2c3 GND -400V c5 signal c4 0 ohms c6 -In case of spark C4 will be discharged through C5 (1k Ohms @ 1Ghz, 100k@10Mhz) It will create a peak current of 500V/1k=0.5 A during a few ns +500V/100K= 5mA during 100ns (0.1A with R1=5K) the average value is in this case in the range of 3nA (R1=50K) and 10nA (R1 =5K) Here also many pads should be sparking at the same time (up to 4uA measured) (500 pads have an area of 15mm x 15mm) Strip 0.1mm x 10cm pad R1