ECAL status and plans

Current status and problems

Recent activities: C-W noise studies summary; Lab measurements of LED Monitoring system performance;

Future plans

by Yu. Gilitskiy, T. Kvaratskheliya, I. Machikhiliyan

and special thanks to P. Shatalov for very useful laboratory studies of

electronics part

Current status-I

optimization of voltage delivery/control boxes – finished; integrators for PM current measurement: installed, adjusted and connected to dedicated control box; PIN-diodes system: fine gain tuning to account for large PM gains spread over ECAL is finished; results of this procedure are to be checked;

Current status-II: access summary

malfunctioning PM channels: few power lines are fixed; C-side: about 30 connectors on signal cables are repaired (FEB side); More problems are expected. Typical pattern: small / unstable PM signal; wall side ~ 40 PM/C-W doublets are replaced A-side: residual problems in cabling (swapped connections, wrong mapping, bad contact, etc) are fixed; List of few problematic FEB channels was sent to Jacques;

Current status-III: access summary (cont)

Optics of the monitoring system:

3 optical bundles are found to be damaged irreparably: LED groups A3.08.4; A3.11.4 and A1.05.1 (partially)

Besides: 5 (C) + 8 (A) cells with absent / week LED signal due to damaged single optical fibers

Short-circuited power lines

After voltage delivery / control boxes modification: got 7 cases of short-circuits in low voltage power lines (2 in March, 5 in April) All cases show the same pattern:

short-circuit is in +6V chains; short-circuit is due to not recovered resettable fuse (new type is used in modified version) in the voltage delivery / control box; short-circuit happens after (? incorrectly preformed ?) low voltage power supply (MARATON) shut-down (e.g. power cut);

Two versions of what is happening: small fraction of fuses is defective. As soon as all of them will malfunction and replaced, the problem disappears; abnormally high currents sometimes appear at the moments of ECAL LV power sources shut-down for reasons unknown. These reasons must be understood;

Short-circuited power lines-IISeries of laboratory tests:

fuse always recovers while it experiences one single trip (several current and voltage settings are checked); latest news: fuse can burned if:

after the first trip it trips again several times with time interval in-between less that ~30 seconds. Than it goes to an intermediate state. If the fuse stays in this state with the voltage supplied for a certain time, it becomes damaged;

NOT TO SWITCH ON ECAL LV RIGHT AFTER POWER CUT, BUT WAIT ~30 MINUTES MIGHT

BE A SOLUTION

Short-circuited power lines-III Our proposal is:

avoid unnecessary switching ON/OFF MARATON LV;if there is a need to switch it OFF (e.g. for preshower people) – contact us first, we will check current ECAL conditions;each turning ON/OFF of MARATON should be mentioned in CALO logbook together with the status of ECAL MV Agilent power supply; request to ECS group: is that possible to record automatically all moments when MARATON’s and also Agilent’s channels are turned ON/OFF? Also useful: to mention in CALO logbook time of all power cuts

Correct procedure to switch OFF the ECAL: Set zero HV codes on ECAL PMs (wait for confirmation from SW); Set zero MV on Agilent power supply (wait for confirmation from SW); Switch OFF LV (MARATON). All 4 dedicated channels of MARATON power supply must be turned OFF at once. DO NOT TURN OFF single channel, it can cause MARATON supply failure;

In case of any emergency shut-down Agilent is turned off first, only then – MARATON, not contra vise!

Pick-up noise appears regularly in time with the frequency as twice as high as the one of C-W base internal pumping oscillator f (f=60 kHz). Pulses have complex shape, typical amplitude less than 3 mV and duration much less than the period of internal oscillator; On the pedestal distribution the effect of the noise manifests itself as rare tails around the core Gaussian distribution of “ideal” pedestal;

C-W noise studies-I

C-W noise studies-II

Data from all ECAL R/O crates (CAT DAQ + random trigger + LEDs OFF);

Two settings for C-W base feeding medium voltage - 50V and 80 V;

PM gains range: from 1K to 300K; Noise characterizing parameters are chosen to be:

i. fraction of entries outside the range <P> −2σ ≤ I(ADC) ≤ <P> +2σ (<P> − 3σ ≤ I(ADC) ≤ <P> + 3σ ), where I(ADC) is ADC reading, while <P> and σ are position and width of the pedestal as obtained from Gaussian fit of the core distribution.

ii. noise sweep, estimated according to the minimal and maximal values reached by ADC readings in the current r/o channel;

MVU

C-W noise studies-III

Minor dependence on No significant dependence on PM gain in LHCb ECAL operational range;No correlations between channels; The clear difference (factor 1.6 in the tails sweep) is observed between Inner cells and the rest of ECAL channels;

MVU

Different gain settings from 1K to 300K in the same r/o crate #20

Noise sweep (in Et terms) vs r(cm). Black, red and blue – Inner, Middle and Outer cells

C-W noise studies-IV Summary/Conclusions:

channel-to-channel difference in the noise level can be neglected for all cells, belonging to the same section (at nominal gain settings); pedestal distributions for groups of channels of the same section type can be summed up. Reason: resulting net distributions (either one per ECAL section or one per readout crate) comprise much higher statistics in comparison with the ones for individual channels and therefore more useful for further studies Details can be found in Internal note LHCb-2008-016 Beyond the note. News from the lab: difference between sections could be attributed to the interference in grounding lines of the flat power cable. The size of effect depends on the distance between neighboring C-W bases on the line, i.e. cell size;

Further step - MC studies: it is proposed to use for Monte Carlo simulations the description of C-W noise in the form of three net pedestal distributions summed up over channels of readout crates #13 (Inner), #12 (Middle) and #9 (Outer), which are obtained under the conditions of nominal PM gains and “pessimistic” value of equal to 80 V. use these distributions to implement C-W noise in Monte Carlo simulations and to understand its impact on ECAL performance (in progress, by A. Kozlinskiy)

MVU

ECAL monitoring system performance lab studies

LED drivers: time delay between arrival of LED fire signal and LED flash: 39.6±1.8 ns (on the basis of 55 LED drivers); PIN amplifiers (on the basis of 31 amplifier):

time delay 12.5±0.5 ns gain dispersion: r.m.s. < 0.9%

Further plans

ECAL system now is in more or less final shape. The majority of channels is operational; Next step: study of the whole detector performance. In that purpose time sharing with other commissioners is needed:

near future: collect several samples with significant LED statistics in order to develop analyzing algorithms (will be used further for LED based calibration and monitoring); later, periodically: several hours of DAQ in order to study detector behavior at different PM gain / LED intensity settings and to understand long-term stabilities of the PM and PIN responses;

Spare slides

Brief comments on modificationGoal: stabilization and increase of low voltage on ECAL C-W basesChange: new type of (resettable) fuse in LV chains. Fuses of old type have large dispersion in internal resistance R, which, together with large value of R itself, resulted in noticeable voltage drop on it. As a consequence, there is an undesirable decrease of LV on the C-W bases. The value of the effect depends also on the load of the line (i.e. number of C-W bases served by it).

Fuse data sheet

Laboratory studies: burn tests

1. Operational conditions check: at U=8V no trip up to I=0.4A; Internal resistance value R is 1.6 Ohm and

does not change2. Trips at “soft” conditions: U=8V, I varies from 0.5 up to 3A:

1. After the first trip at 0.5A R increases up to 2.3 Ohm2. Next trips: fuse recovers to the value R=2.3 Ohm; recovery time is

~10min3. Trips at “hard” conditions:

1. high U=24V, I varies from 3 to 5A. Fuse recovers to the value R=2.3 Ohm; recovery time increases to 60 min;

2. Data sheet max U=30V. R increase to 3.9 Ohm, but fuse is still operational

3. I=10A and U=60V. Fuse recovers to the value R=3.9Ohm; it is still operational

Even at the abnormal current/voltage conditions, which can not be achieved in the ECAL system, it was not possible to reproduce

an effect of non-recovery in the lab