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Tracker Week, January 20021 Lab measurements and simulations of hips previously presented APV measurements* assumed signal divided.

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Presentation on theme: "Tracker Week, January 20021 Lab measurements and simulations of hips previously presented APV measurements* assumed signal divided."— Presentation transcript:

1 Tracker Week, January Lab measurements and simulations of hips previously presented APV measurements* assumed signal divided equally between 7 channels -> significant deadtime predictions for CMS but relative absence of –ve saturated baseline events (no signal) in test beam data either beam test analysis biased (true for results presented previously) or 7 channel model pessimistic (probably also true) => worth investigating effects of different hip signal distributions OUTLINE Introduction Simulations (SPICE) New deadtime measurements for hip signals on one/two channels Hit loss rate predictions for new deadtime measurements Summary *http://cmsdoc.cern.ch/Tracker/managment/Agenda_GTM/GM_01_12/Mark_CMShipstalk.ppt

2 Tracker Week, January ~ 8 mip range X5 hip event shows up as saturated signals in several channels APV output range only ~ 8 mip (0.7 MeV) so no information on actual signal size in saturated channels First measurements on APV modelled hip charge shared equally between 7 channels (choice simply governed by number of chans available on test setup) Recoil nucleus should have short range (e.g. < 43  m for E < 100 MeV) but true situation more complicated V. large signals on one/two channels still give > 0.7 MeV signals on neighbours due to inter-channel capacitance saturated signals in 4 strips in this example X5 hip event Introduction

3 Tracker Week, January v CM vivi v o = -v i + v CM hip signal SPICE simulations R (on hybrid 1/chip) preamp s.f. inverter source follower O/Pinverter O/P sensor APV motivation: can’t see what’s going on inside chip otherwise model: 128 channels with nearest neighbour interstrip capacitance (10pF) and AC coupling to APV I/P preamp o/p (after s.f.) linear to ~ 50 mips (4.5 MeV) inverter O/P linear to ~35 mips (3.2 MeV) signals > ~ 50 mips on a single channel cause that channels inverter to draw max current -> significant voltage disturbance on v CM mip 10 mip steps

4 Tracker Week, January v CM vivi v o = -v i + v CM Simulations (2) R (on hybrid 1/chip) results here for 200 mip (18 MeV) signal on one channel only saturated signal in hip channel big signal in nearest neighbours (~25 mip), shorter duration combination -> transient disturbance v CM on R v CM disturbance couples to inverter O/Ps of all channels reduced value of R reduces effect “spikey” behaviour of v CM interesting, could be decoupled preamp s.f. inverter source follower O/P inverter O/P v CM hip channel nearest neighbours non-hip channel

5 Tracker Week, January Lab measurements - “improved” setup for charge injection 7 APV I/Ps see hip charge shared equally hip charge injected on one or two channels other channels see signal due to interstrip capacitance 10pF previous 111 mips500 mips1111 mips These results for hip charge injection on one channel only Inter-channel capacitance -> signal sharing and saturated signals in several channels i.e. localised hip signal still shows results consistent with beam data this study 10 MeV 45 MeV100 MeV

6 Tracker Week, January Deadtime measurement technique Inject and measure amplitude (in APV O/P frame) of normal size signal sweep injection time of hip signal normal signal disappears during period when hip signal causing baseline saturation for all channels unplug normal signal and repeat to get baseline subtract baseline measurement from measurement with signal -> result gives deadtime = period during which the chip is insensitive to signals all measurements here in deconvolution mode t inject normal signal trigger on normal signal latency vary injection time of hip signal

7 Tracker Week, January Deadtime measurements hip signal confined to 1 channel only Deadtime dependence on hip signal size characterised by a threshold and then rising to a saturated level Main difference when R -> 50 is increase in energy threshold required to produce deadtime Deadtime saturation level ~125 ns R=100  (5 bunch crossings) ~100 ns R=50  (4 bunch crossings) 10 MeV 100 MeV

8 Tracker Week, January Deadtime measurements hip signal shared between 2 channels Threshold energy for onset of deadtime significantly worse than for signal on one channel case Significant improvement in threshold energy and deadtime duration when R -> 50  Deadtime saturation level ~300 ns R=100  (12 bunch crossings) ~100 ns R=50  (4 bunch crossings) 10 MeV 100 MeV

9 Tracker Week, January v CM measurements vs. simulation Voltage measured (with scope probe) on inverter supply resistor -> some similarity between measurement and simulation Decoupling inverter supply effective at removing spike Effect on deadtime worth investigating simulationmeasurement

10 Tracker Week, January Deadtime measurements – effect of decoupling inverter supply Results here for signal shared between 2 chans Effect of decoupling “spike” on inverter supply quite dramatic for R=100  case, Less so in 50  case, but still some improvement 10 MeV 100 MeV

11 Tracker Week, January Deadtime measurements – comparison with previous result Results here for 100  inverter supply resistor (existing situation) 7 channel case shows smooth rise (up to ~ 60 bunch crossings at high energies) one/two channel + inter-channel capacitance model show big reduction in saturation level over 7-channel equal sharing model (5 – 12 bunches) but deadtime starts to appear sooner in 2 chan case and hit loss calculation sensitive to this threshold 111 MeV 1111 MeV

12 Tracker Week, January Deadtime measurements – effect of decoupling and/or reducing R Deadtime dependence on whether hip signal on 1 or 2 channels significant only in R=100  case Decoupling and/or reducing R -> substantial improvement in deadtime Can parameterise deadtime and use to predict deadtime in CMS but already obvious that R-> 50  and/or adding decoupling will give significant improvement

13 Tracker Week, January X5 CMS Prob. of missing hit (E) = Prob.(E)*[deadtime(E)/25ns]*128*occupancy Hit loss rate predictions - method Total probability of hit loss per layer =  Prob.(E) (note: above plots taken from previous talk (7 – channel case)) E Prob.(E) deadtime(E) Prob. of missing hit (E) 10 MeV100 MeV1 MeV 10 MeV100 MeV

14 Tracker Week, January Total probability of hit loss (per 300(500)  m layer, per % occupancy) Hit loss rate predictions – for CMS (G.H.) signal shared equally between 7 chans (previous result adjusted for latest simulations (M.H.) signal shared equally between 2 chans (+ inter-channel capacitance) R=100  R=50  0.33 (0.76) %0.20 (0.49) % 0.34 (0.65) %0.023 (0.053) % 7 chan vs. 2 chan: No significant difference in hit loss prob. for R = reduction in deadtime at high hip energy compensated for by lower threshold for deadtime onset 7 channel results: R: 100 -> 50 gives ~ 40% reduction in hit loss probability but in 2 channel case get better than order of magnitude reduction - presumably reduction in v CM transient much more effective for charge distribution produced by 2 chan. + inter-chan capacitance model not calculated exhaustively but other variants (1 chan only and/or decoupling) will give results similar to 2 chan/50  case

15 Tracker Week, January Threshold hip energy required for saturated baseline APV lab measurements 7 – channel equal sharing9 – 18 Mev 1 chan + inter-channel capacitance13 – 16 MeV 2 chan + inter-channel capacitance6 – 8 Mev simple linear CM assumption depends on analogue O/P baseline position if ¼ to ½ output range25 – 50 MeV discrepancy => saturated baseline threshold = non-linear function of hip energy actual hip energy required to saturate baseline depends on details of charge distribution

16 Tracker Week, January Summary Modelling hip signal as large charge deposited in one or two channels -> saturated signals in more channels if inter-channel capacitance included Resulting hit loss rate prediction (2 chan.) similar to previous 7 chan equal sharing measurements but order of magnitude improvement if R -> 50   relative hit loss rate could go from 0.3% -> 0.02% per 300  m layer per % occ.) One/two channel results here suggest deadtime resulting from hip events could be in range 5 – 12 bunch crossings for existing inverter power scheme -> some evidence for this in existing X5 beam data. Accurate determination of hit loss rate in CMS depends on: how well hip spectrum known (magnitude and rate) hip energy distribution between channels (will vary from event to event)


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