1. Update from Wellesley SF6 + Micromegas & Multi-channel DAQ
James Battat & Catherine Nicoloff
2017 June 7

2. Summary Detector description
Single-channel work: Fe-55 spectra with Micromegas in 30, 40 and 50 Torr SF6. Now integrating preamp pulses (no shaper)
DAQ electronics from BNL for 1000-channel readout. Development of FPGA back-end to handle data stream (buffer, trigger, save).

3. micromegas

4. 10 x 10 cm2
Gap: 128 um and 256 um
Strips:
* 200 um pitch
* 500 channels in x, * 500 in y

5. Resistive strip micromegas J. Burnens, R. de Oliveira et al
Resistive strip micromegas J. Burnens, R. de Oliveira et al., arXiv:

6. Effective gas gain vs. drift field, 30 Torr Fixed ampl: 550V over 256um = 21.5 kV/cm = 720 V/cm/Torr
400
Vdrift = 1250V
From last presentation (used a shaper)
Gain
150 4 16
Reduced Drift Field [V/cm/Torr]
Vdrift = 750V
Note: results are from an automated fitting routine that is still under development, some wiggle in y-values expected as we refine...

7. Gas gain studies: system diagram (single channel readout)
to scope (then integrate waveforms off-line)
= Vamp
= Vdrift

8. SF6 results
Gas gain demonstrated at 30, 40 and 50 Torr SF6 using a 256 um gap micromegas.
Have not yet (re)visited 20 Torr.
Max gain so far is ~2000 (in 40 Torr) (though gain calibration very preliminary, trust at 50% level...).
Have a 128um device (not yet used in SF6). Interested to buy a 512um device from CERN.

13. Brookhaven National Lab DAQ Developed or LAr, but works with NITPC
At BNL, help from:
Drs. Hucheng Chen and Gianluigi de Geronimo and Jack Fried
Custom FPGA development (Back-end) by Wellesley & Boston University (Prof. Martin Herbordt and grad student Ethan Yang).
Have demonstrated circular buffer with 31 Gbps throughput.
Challenge: BNL Front-End FPGA code is undocumented...

14. Paper written for IEEE High Performance Extreme Computing 2017 Conference

15. Slides from last time (2017-01-18) for reference

16. First believable spectrum (30 Torr)
Vamp = 555 V (256um gap)
Eamp = 21.7 kV/cm = 720 V/cm/Torr
Vdrift = 1050 V
Edrift = 330 V/cm = 11 V/cm/Torr
Gas gain ~ 260

17. Effective gas gain vs. drift field, 30 Torr Fixed ampl: 550V over 256um = 21.5 kV/cm = 720 V/cm/Torr
400
Vdrift = 1250V
Gain
150 4 16
Reduced Drift Field [V/cm/Torr]
Vdrift = 750V
Note: results are from an automated fitting routine that is still under development, some wiggle in y-values expected as we refine...

18. Gas gain vs. amplification, 30 Torr Fixed Vdrift (oops) = 1200V
Gas gain vs. amplification, 30 Torr Fixed Vdrift (oops) = 1200V. Drift field range: 420 to 450 V/cm
Gas Gain (effective)
1000
100
Amplification Field [V/cm]
Vamp range: 530 to 575V
Eamp/P range: 690 to 750 V/cm/Torr
1e4
1e5