PS Timing & Alignement Progresses 17 April 2008 LPC Clermont

2 Delays from Fibres MAPMT ( 64 channels ) scintillator Clear Fiber ( L c = m ) WLS Fiber ( L w = m ) Fiber in Grooves ( m ) From Pascal PS/SPD Comm. Meeting Tue. 5 Feb From Evgueni & Sergey Neglected … unknown impact Various optical fiber lengths in front of PMTs introduce various propagation delays  signals in time at detector input no more in time on PMTs Expected delay from fibre as ( typical ) and

3 Delay Compensation in VFEs FEB ADC 1 st capture FEB ADC 1 st capture VFE integration FEB cycle nFEB cycle n+1 FEB cycle n-1 VFE integration signal p-e from PMT FEB FEPGA 2 nd capture FEB FEPGA 2 nd capture signal p-e from PMT Translate VFE clocks to ‘follow’ fibre delays Other phasers must follow the VFE shift … Goal: ensure ‘equal sampling’ of signals

4 FE / VFE Synchronisation plateau FEB cycle n-1 FEB cycle n FEB phaser values are functions of the VFE clock delay : caution: ‘arbitrary’ FEB cycle  FEB ~= 8

5 Cosmic Setup Arbitrary time origin:  relative VFE clock delays follow fibres  T  global translation such that all signals fall within same FEB cycle SLOTVFERSTADCFEB Example: PRS0 settings Signals in input fall within same FEB cycle From fibres

6 Fiber Delays with LEDs: Schematic MAPMT ( 64 channels ) scintillator Clear Fiber ( L C = m ) WLS Fiber ( L W = m ) Fiber in Grooves ( L G = m ) LEDFlash LED Trigger Cables ( L T ~ 3-8 m ) Trigger Signal LEDTSB / CU ( ) ‘Re-measure’ fiber lengths using LED flashes From Evgueni & Sergey

7 Fiber Delays with LEDs: Protocol q to-1 q to (1) Measure LED arrival cycle within FE-PGA RAMS (2) Locate LED pulse within cycle by moving VFE phase  t Tuning: detect ‘close to peak’ position of LED pulse by looking for minima of: close to peak off peak

8 1 FEB 64 channels VFE Phase  LED Peak Position within VFE Cycle

9 Fiber Delays with LEDs: Corrections (3) Average  t over all (32-64) channels for each FEB  ( taken as measurement error ) (4) Subtract LED trigger start cable delays ( From Evgueni & Sergey )  (5) Compare to fibre lengths delay ( ‘clear’ from Pascal / ‘WLS’ from Evgueni & Sergey )   Fit LED measurement to fibre delays with a single arbitrary time origin  t 0 as fit parameter Measured fibre delay with LEDs:

 t Fibre (ns) Inner From LEDs From fibres lengths 1 single time origin 30 Error 3  (99% CL) ‘statistical’ only

11 Fiber Delays with LEDs: Systematics (  ) There are remaining biases that can be corrected per trigger cable  Fit time origin  t 0 per trigger cable now ( typical correction: 2-3 ns ) (  ) The ‘inner’ detector parts have has a  13 ns offset as regard to outer parts  and (  ) Measurement related to the trigger cable #2 of SM2 are inconsistent by 5 ns: already the very top level before any correction from trigger cable lengths (  ) Measurements related to the trigger cables #3 in SM1 and SM2 are not constrained ( 1 single cable per FEB measured ) LED trigger cables were indicated by their number within a SM on the previous plot, close to the corresponding ‘measurement dot’. - 1 Trigger cable triggers flashes on 1 to 3 FEBs

 t Fibre (ns) From LEDs From fibres lengths 1 time origin per LED trigger cable ?? 30 Error 3  (99% CL) ‘statistical’ only

13 Conclusion Delays computed from fibres length are in fair agreement with LED measurements / use these delays as initial guess for PRS timing  Systematics left: - SM2 (miss-cabling ???) - Inner wrt Middle/Outer (  LEDs ???)