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New approach to CPC design

New approach to CPC design. It is my 1-st presentation from LNF/INFN (Frascati ). The scientific work is still under development and the new ideas have to be tested…. Triggered by P.Campana Why results on cross-talks obtained with small chamber in May 02 are somehow better

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New approach to CPC design

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  1. New approach to CPC design A.P.Kashchuk (LNF/INFN), Frascati)

  2. It is my 1-st presentation from LNF/INFN (Frascati) The scientific work is still under development and the new ideas have to be tested… Triggered by P.Campana Why results on cross-talks obtained with small chamber in May 02 are somehow better than with the large M0 prototype tested in October 02? A.P.Kashchuk (LNF/INFN), Frascati)

  3. I’d like to add: ? ? • 2 problems observed in beamtests • have to be explained and suppressed: • rather high cross-talks from wires to pads; • - double and multiple TDC spectra Problems mentioned here were observed already in M2R1 and other prototypes built at CERN, as well as in Ferrara’s prototypes; 50% crosstalks observed in some conditions in M3R3 in October 2002 beam-tests at operational HV What the reason? A.P.Kashchuk (LNF/INFN), Frascati)

  4. Cross-talks ? A.P.Kashchuk (LNF/INFN), Frascati)

  5. Cross-talks along the wires (longitudal) perpendicular to wires (transverse) Longitudal crosstalks are less studied and much less suppressed A.P.Kashchuk (LNF/INFN), Frascati)

  6. According to specification (LHCb 2000-061, W.Riegler) Cross-capacitance Cwp will be increased with pad size, as shown: LNF M0 Cwp=0.475hw (pF) where h, w are pad height and width (cm) A.P.Kashchuk (LNF/INFN), Frascati)

  7. Let’s measure: (very good agreement with table shown above) Cwp measured in large M3R3 is absolutely similar A.P.Kashchuk (LNF/INFN), Frascati)

  8. The original idea was following: Cross-talks from wire strips to pads (longitudal) will be reduced with grounding wire strips through HV-capacitors A.P.Kashchuk (LNF/INFN), Frascati)

  9. RC-model (Rwire =90 Ohm/m) Only capacitive coupling is taken into account in this model Assumed that width of wire strip is equal to cathode pad Wire strip with 4 wires Signal from particle Cathode pad current source HV-capacitor grounded on one side, as shown A.P.Kashchuk (LNF/INFN), Frascati)

  10. Wire strip as a transmission line, i.e. LC-model (first proposed by LNF group) Cathode pad current source Each wire can be considered as a transmission line Wires in strip are connected in parallel: L reduced, C increased (product LC is the same) A.P.Kashchuk (LNF/INFN), Frascati)

  11. Recently it has been found: the wire strip is ringing (response of wire strip in small LNF prototype made with injector) HV-capacitor 680pF directly grounded f=95 MHz The ringing frequency depends on inductance in series to HV-capacitor (what the reason?) f=60 MHz A.P.Kashchuk (LNF/INFN), Frascati)

  12. Cross-talk profile from wires to cathode pads in the large M3R3 prototype Volt. step on strip (strip is floating) 20ns/div Pad-1 (15%) Ringing 18 ns Central Pad Ratio 2-nd/1-st peak 20% Pad+1 (20%) A.P.Kashchuk (LNF/INFN), Frascati)

  13. Fine waveform structure at voltage rise time 1.5ns: One can see 4 ns oscillation High frequency is due to LC of the transmision line itself A.P.Kashchuk (LNF/INFN), Frascati)

  14. Response of wire strip in small LNF prototype made with Current Injector Ringing 13ns Strip is grounded through 680pF, with adding inductance period is increased A.P.Kashchuk (LNF/INFN), Frascati)

  15. Equivalent circuit 1.Inductance blocks HV-capacitor effect Wire strip Terminated end Cathode pad High cross-talk: Compare to ideal case: 2.Another parasite effect Assumed But!!! A.P.Kashchuk (LNF/INFN), Frascati)

  16. What LC-model shows? with HV-capacitors grounded at inductance 3nH in series (perhaps, can be acheaved) 1-side strip termination with 0 Ohm 2-side (peak less factor 2) Peak=1uA Ringing= 8ns Peak=0.5uA Ringing= 3ns A.P.Kashchuk (LNF/INFN), Frascati)

  17. Stray inductance (printed traces) in series to HV-capacitors and full capacitance of the wire strip mainly specify the ringing frequency Green – 3nH Red – 300nH (can be if width of traces 0.25mm, see M3R3) 1-side strip termination with 0 Ohm 2-side termination Green peak=1uA Red peak=1uA Ringing=30ns Green peak=0.5uA Red peak=1uA Ringing=20ns A.P.Kashchuk (LNF/INFN), Frascati)

  18. Correct strip termination with 377Ohm can not be used 1- signal at far end to capacitor Ohm 2-side termination through 680pF At 1-side termination amplitude will depend on signal position along the strip (see next slides) 2- middle 3- near end No ringing, waveforms are independed to position of the signal source, but the highest crosstalks will be in this case A.P.Kashchuk (LNF/INFN), Frascati)

  19. Inductance in series to HV-capacitors (1-side termination with 680pF and 50 Ohm) Same schematics No ringing Peak independ on Lstray due to 50 Ohm , but not enough cross-talk attenuation 3 1 2 Green=3nH Red=100nH Scale +/-2uA 10ns/div A.P.Kashchuk (LNF/INFN), Frascati)

  20. Inductance in series to HV-capacitors (1-side termination with 680pF and 0 Ohm) Same schematics Better attenuation, but ringing at R=0 1 2 3 Scale +/-2uA 10ns/div Green=2nH/Ringing 200MHz Red=100nH/Ringing 70MHz A.P.Kashchuk (LNF/INFN), Frascati)

  21. Inductance in series to HV-capacitors (2-side termination with 680pF and 20 Ohm) Same schematics Good cross-talk attenuation factor at 20 Ohm High inductance leads to ringing even at R=20 Ohm and drastically reduces cross-talk attenuation 3 1 2 Red=100nH/Ringing 100MHz Green=3nH/No ringing Scale +/-2uA 10ns/div A.P.Kashchuk (LNF/INFN), Frascati)

  22. Inductance of printed trace (example): if w=0.25mm trace width (in M3R3 prototype) h=1.5mm pcb thickness l=3-10cm length of trace (in M3R3 prototype) then L=100-1000nH if w=1.2cm then L=5nH can be achieved @ C=100pF A.P.Kashchuk (LNF/INFN), Frascati)

  23. Ringing on wire strip can double/multiple signals and TDC spectra Threshold defined experimentally: for wire readout –7fC for cathode (single) – 5fC FEE noise 50e/pF is not the first reason for threshold choice, mainly cross-talks define threshold, at efficiency 95%/gap Dynamic range of signals in CPC is large (100) Average signal 50fC So, high probability for after-pulsing can be found at bad wire strip termination and imperfect layout in CPC at any frequency of ringing (it depends on design) A.P.Kashchuk (LNF/INFN), Frascati)

  24. If Cstrip=Cwire is high? +/-2uA Excellent result +/-0.2uA No ringing and high cross-talk attenuation A.P.Kashchuk (LNF/INFN), Frascati)

  25. ! Conclusion CPC design can be improved following the way: No ringing must be on the wire strips at perfect design 1.No wire segmentation is needed in CPC design - one of theeffective way No HV-capacitors and resistorrs (cheaper and much easy design), wires are connected to one HV-resistor. Minimisation of the trace inductances has to be done in the Combined readout chambers, which dumps effect of low impedance. 2.Double Cathode Readout scheme,perhaps, can be used in some cases below M3R3 also effective way at large Cwires(it allows increase threshold at fixed HV) already tested in M1R1 with excelent results (because very low Cwp and good attenuation of the cross-talks from wires) Happy end ? A.P.Kashchuk (LNF/INFN), Frascati)

  26. Summary Voltage zero must be on the wire strips at perfect CPC design, i.e. LNF M0 ? Single CRO. No wire segmentation Double Cathode readout (CRO) below M3R3. No wire segmentation A.P.Kashchuk (LNF/INFN), Frascati)

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