Presentation on theme: "A potential cost saver for the CMS GEM upgrade: GEM readout with zigzag strips Marcus Hohlmann Florida Institute of Technology CMS GEM Workshop III, April."— Presentation transcript:
A potential cost saver for the CMS GEM upgrade: GEM readout with zigzag strips Marcus Hohlmann Florida Institute of Technology CMS GEM Workshop III, April 20, 2012
Motivation Cost is one of the biggest current issues for the CMS GEM upgrade project The single-largest budget item in the current GEM budget estimate is electronics: ~3M out of 6.4M total (TP CMS IN 2012/001) Clearly, we should seriously look for ways to reduce the electronics cost if possible –One potential real cost saver would be the significant reduction of readout channels Can a zigzag strip readout help with that? 4/20/2012 GEM Workshop III - M. Hohlmann 2
Previous BNL 4/20/2012 GEM Workshop III - M. Hohlmann Zigzag strips: Charge sharing among adjacent strips allows quite sensitive position-interpolation in x-direction We are sacrificing the measurement of the 2 nd coord. (y) to gain precision in the 1 st coord. (x) CMS GE x/1 detectors are currently intended for 1D-coordinate measurements, so the zigzag approach is applicable to these detectors x (measured coordinate) Previous exp. studies show <100 µm resolution with 2 mm strip pitch is possible: y 3 Concept: ava- lanche BNL
Zigzag strips vs. straight strips 4/20/2012 GEM Workshop III - M. Hohlmann 4 Can reduce # of readout channels (and electronics cost) by 70% of current design Improve resolution by factor 3-4 Pitch [mm]Typical Resolution [µm] Zigzag strips & analog r/o2.080 Straight strips & VFAT (current design, short end) Improvement factor w/ zigzag strips A “figure of merit”: 3.33 × 3.75 = 12.5 ~ Potential for order of magnitude improvement over current design Well worth a try! &
Zigzag r/o PCB (10cm × 10cm) 4/20/2012 APV25 Hybrid (using only 38% of 128 ch.) + SRS Readout Board for std. CERN 10cm×10cm Triple-GEM Detector 2 sets of 10cm zigzag strips with different zigzag pitch (along strip) BNL/FIT/Stony Brook Collaboration 24 fine zigzag strips 24 coarse zigzag strips LEMO footpads GEM Workshop III - M. Hohlmann 5 PCB with solder finish CAD Design by C. Pancake, Stony Brook 2 mm 0.5 mm 1 mm Solid ground plane on the back side.
2 nd batch: Gold plating finish 4/20/2012 GEM Workshop III - M. Hohlmann 6 Ordered second batch with gold plating finish because hot-air solder leveling (HASL) finish shows non-uniform surfaces: HASL Au plated Much higher surface quality
WHAT ABOUT NOISE? 4/20/2012 GEM Workshop III - M. Hohlmann 7 First commissioning step addressed noise question: Measure pedestals and compare with regular straight strips Does the noise increase substantially due to the increased strip area and capacitance?
Pedestal Distributions 4/20/2012 Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane: ADC channel # ev. per ch. ADC channel # ev. per ch. APV ch. 63 (example) pedestal width: r.m.s 3 → 4 cts. GEM Workshop III - M. Hohlmann 8 straight strips zigzag strips APV25 Hybrid (using only 38% of channels) + SRS
Pedestals for all channels 4/20/2012 Pedestal width (rms) [ADC counts] APV channel number 48 channels connected to zigzag strips (24+24) channels not connected (open APV inputs) Channels connected to LEMO footpads (5) Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane: GEM Workshop III - M. Hohlmann 9
First pulses with zigzag r/o 4/20/2012 GEM Workshop III - M. Hohlmann 10 GEM stack being assembled on zigzag r/o board Completed Triple-GEM with zigzag r/o board under gas, HV, and x-rays (Cd 109 ) Strips ganged together using adapter board plugged into a Panasonic connector Pulses recorded with ORTEC preamp and (slow) lin. amp. Currently setting up for cosmics test with APV + SRS…
30cm × 30cm zigzag PCB 4/20/2012 GEM Workshop III - M. Hohlmann 11 Plans for next design: Design and build a zigzag readout pcb for the 30cm × 30cm self-stretch CMS GEM (on order w/ Rui) 128 zigzag strips of 10cm length covering the full 30cm width & read out by a single APV25 hybrid + SRS Test also 30cm long strips on same board (given the good noise performance of the 10cm long strips) ~ 300 mm Photo-montage
Impact on electronics design 4/20/2012 GEM Workshop III - M. Hohlmann 12 Potential for removing the need for 2/3 of the electronics of current baseline design: from Paul Aspell’s talk on Thu. 1
Implications Potential for saving 70% of readout channels and ~50% (?) of electronics cost, could mean potentially saving MCHF on the project Simplifies also cooling, cabling, power, etc., which would lead to additional cost savings Total project cost < 5 MCHF possible ?! Analog pulse height measurement is mandatory for charge interpolation, so VFAT3 would not work → need a GdSP design 4/20/2012 GEM Workshop III - M. Hohlmann 13
Conclusion & Outlook Noise increases by only 1.5 ADC counts (~ 0.1% of range) for zigzag strips compared w/ straight strips. Encouraging! Can potentially read out one GE1/1 strip row with single 128-ch. front-end hybrid while improving spatial resolution; could lead to substantial channel number & cost savings. Next: –Measure spatial resolution using tracked cosmics –Test zigzag prototype in 2012 test beam –Design, produce & test larger prototype boards 4/20/2012 GEM Workshop III - M. Hohlmann 14