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GEM Readout with Zigzag Strips: A Potential Cost Saver for the CMS GEM Upgrade

This presentation discusses the use of zigzag strips for the readout of the CMS GEM upgrade project, which has the potential to reduce the number of readout channels and electronics cost. The presentation includes previous work, PCB designs, noise analysis, and implications for the project's cost and design.

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GEM Readout with Zigzag Strips: A Potential Cost Saver for the CMS GEM Upgrade

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  1. A potential cost saver for the CMS GEM upgrade: GEM readout with zigzag stripsMarcus HohlmannFlorida Institute of Technology CMS GEM Workshop III, April 20, 2012

  2. 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? GEM Workshop III - M. Hohlmann

  3. Previous Work @ BNL Previous exp. studies show <100 µm resolution with 2 mm strip pitch is possible: Zigzag strips: y ava-lanche BNL x (measured coordinate) Concept: • Charge sharing among adjacent strips allows quite sensitive position-interpolation in x-direction • We are sacrificing the measurement of the 2nd coord. (y) to gain precision in the 1st coord. (x) • CMS GE x/1 detectors are currently intended for 1D-coordinate measurements, so the zigzag approach is applicable to these detectors GEM Workshop III - M. Hohlmann

  4. Zigzag strips vs. straight strips & Can reduce # of readout channels (and electronics cost) by 70% of current design Improve resolution by factor 3-4 A “figure of merit”: 3.33 × 3.75 = 12.5 ~ Potential for order of magnitude improvement over current design  Well worth a try! GEM Workshop III - M. Hohlmann

  5. Zigzag r/o PCB (10cm × 10cm) 2 sets of 10cm zigzag strips with different zigzag pitch (along strip) PCB with solder finish 24 coarse zigzag strips 24 fine zigzag strips 1 mm CAD Design by C. Pancake, Stony Brook LEMO footpads 0.5 mm APV25 Hybrid (using only 38% of 128 ch.) + SRS Readout Board for std. CERN 10cm×10cm Triple-GEM Detector 2 mm 2 mm BNL/FIT/Stony Brook Collaboration Solid ground plane on the back side. GEM Workshop III - M. Hohlmann

  6. 2nd batch: Gold plating finish Ordered second batch with gold plating finish because hot-air solder leveling (HASL) finish shows non-uniform surfaces: HASL Much higher surface quality Au plated 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? What about noise? GEM Workshop III - M. Hohlmann

  8. Pedestal Distributions Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane: # ev. per ch. straight strips ADC channel APV ch. 63 (example) pedestal width: r.m.s 3 → 4 cts. # ev. per ch. zigzag strips APV25 Hybrid (using only 38% of channels) + SRS ADC channel GEM Workshop III - M. Hohlmann

  9. Pedestals for all channels Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane: Pedestal width (rms) [ADC counts] 48 channels connected to zigzag strips (24+24) Channels connected to LEMO footpads (5) channels not connected (open APV inputs) APV channel number GEM Workshop III - M. Hohlmann

  10. First pulses with zigzag r/o Pulses recorded with ORTEC preamp and (slow) lin. amp. GEM stack being assembled on zigzag r/o board Completed Triple-GEM with zigzag r/o board under gas, HV, and x-rays (Cd109) Currently setting up for cosmics test with APV + SRS… Strips ganged together using adapter board plugged into a Panasonic connector GEM Workshop III - M. Hohlmann

  11. 30cm × 30cm zigzag PCB • 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) Photo-montage ~ 300 mm GEM Workshop III - M. Hohlmann

  12. Impact on electronics design  Potential for removing the need for 2/3 of the electronics of current baseline design: from Paul Aspell’s talk on Thu. 1 GEM Workshop III - M. Hohlmann

  13. Implications • Potential for saving 70% of readout channels and ~50% (?) of electronics cost, could mean potentially saving 1-1.5 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 GEM Workshop III - M. Hohlmann

  14. 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 GEM Workshop III - M. Hohlmann

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