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sNoise in the Readout of ATLAS LAr Calorimeters

Summer Student Sessions 13 August 2008

Chew Soo Hoon University Of Malaya, Malaysia (caseycsh@cern.ch) Jan Stark LPSC, Grenoble, France (stark@in2p3.fr)

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CERN has just announced the start-date for LHC!

Unhappy channels in the ATLAS LAr calorimeters

10 September 2008

What has been going around or is going around now at ATLAS?

One major issue that keeps everyone busy for these few months…

S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

NOISY CHANNELS IN THE DETECTORS!

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The ATLAS LAr Calorimeters

LAr forward (Fcal)

Tile barrelTile extended

barrel

LAr electromagnetic

barrel

LAr electromagnetic end-cap (EMEC)

LAr hadronic end-cap (HEC)

S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

Hadronic Calorimeter Endcap (Cu-LAr)

Electromagnetic Calorimeter Barrel,endcap (Pb-LAr)

Forward Calorimeter Endcap (W, Cu-LAr)

LAr is the ‘active’ medium and the Pb, Cu and W are absorbers

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The signals detected by LAr calorimeters are very small (~fC or ~µV)…So, huge amplification is needed.

There are about 200 k readout channels in the LAr calorimeters…

Hence, there is a need for the sophisticated electronics creates noises in the readout channels!

Special attention is needed to solve this problem.

Lists of unhappy channels have been discussing in many meetings.

S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

The bunch crossing time=25 nsBut, the drift time in the LAr gap ~ 450 ns

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5S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

Front-end board is read with no input signal to detect noise.

The LAr Readout Electronics in a Nutshell

Front-end board

LAr cell electrodes collect the ionization electrons

The preamplifier amplifies the current signal

The CR-RC2 shaping filter shapes the amplified signals in 3 gains

The SCA stores the signals samples in analogue format

The trigger will select the samples to be digitized

Ionization signal Shaped signal

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An Example of Lists of Unhappy Channels

S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

We wrote a program and displayed the rms values for the empty detectors in histograms to hunt for the unhappy channels!

7S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

• Icell layer ieta iphi region barrel or ec pos or neg FT slot channel gain ped rms detector• 11060 1 116 19 0 0 0 6 3 52 0 974.349 11.2143 0• 13202 1 274 17 0 0 0 7 6 18 0 944.784 30.2519 0• 31093 1 245 60 0 0 0 17 5 117 0 944.236 13.3464 0• 39679 1 63 50 0 0 0 22 2 127 0 983.196 10.7274 0• 47604 1 436 42 0 0 0 26 8 116 0 934.201 17.025 0• 47605 1 437 42 0 0 0 26 8 117 0 916.555 17.8317 0• 47606 1 438 42 0 0 0 26 8 118 0 934.462 17.6548 0• 47607 1 439 42 0 0 0 26 8 119 0 951.01 17.2807 0• 61640 1 264 5 0 0 1 2 6 72 0 967.332 21.1794 0• 68987 1 379 13 0 0 1 6 7 123 0 934.017 17.2334 0• 95734 1 310 43 0 0 1 21 6 118 0 965.97 10.401 0• 113029 1 5 62 0 0 1 31 2 5 0 952.183 14.8943 0• 145444 1 36 46 2 1 0 19 2 36 0 986.41 10.5099 0• 153767 1 31 34 3 1 0 24 5 39 0 968.51 11.6612 0• 178351 1 63 36 4 1 1 14 7 47 0 992.54 11.8433 0• 184619 1 59 44 4 1 1 18 7 43 0 945.703 14.459 0• 315531 3 4 29 0 1 0 3 7 11 1 947.216 11.1312 1• 315570 2 7 31 0 1 0 3 7 50 1 991.372 12.198 1• 326890 2 2 1 0 1 0 10 6 106 1 949.995 13.4252 1• 336547 3 6 63 0 1 0 16 7 35 1 992.161 45.2964 1• 336551 3 6 62 0 1 0 16 7 39 1 973.108 10.9021 1• 336563 3 7 63 0 1 0 16 7 51 1 1012.84 18.8718 1• 336655 3 4 52 0 1 0 16 8 15 1 988.347 10.6762 1• 346250 2 4 37 0 1 0 22 8 10 1 944.161 13.5916 1• 346266 2 5 37 0 1 0 22 8 26 1 952.744 16.1664 1• 346302 2 7 36 0 1 0 22 8 62 1 980.425 12.5365 1• 355842 2 4 8 0 1 1 3 8 2 1 1001.42 16.2463 1

The list we obtained for unhappy channels

It agrees well with the list obtained in the meeting!

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So, we wrote another program and obtained the plots.

S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

To determine why the channels are unhappy…

ADC counts

Num

ber o

f eve

nts

Num

ber o

f eve

nts

ADC counts

Num

ber o

f eve

nts

ADC counts

two humps???

9S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

Again, we wrote another program to display the noise signal in the empty detectors

ADC

coun

ts

Number of samples

The normal noise signal Look for the noise frequency which has the same pulse pattern…

ADC

coun

ts

Number of samples

The abnormal noise signal (from the plot which has two humps)

ADC

coun

ts

Number of samples

10 MHz

ADC

coun

ts

Number of samples

30 MHz

ADC

coun

ts

Number of samples

19.2 MHz

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Conclusions

We suspected the noise is resulted from the power supply which has a frequency of ~19.2 MHz.

S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

But, according to the electronics experts, the noise comes from the input clock somewhere in the electronics.The answer is yet to be found out…