ATLAS LAr Calorimeters Summer Student Sessions 13 August 2008 Chew Soo Hoon University Of Malaya Malaysia caseycshcernch Jan Stark LPSC Grenoble France starkin2p3fr ID: 572637
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Slide1
s
1
Noise in the Readout of
ATLAS
LAr Calorimeters
Summer Student Sessions 13 August 2008Chew Soo Hoon University Of Malaya, Malaysia (caseycsh@cern.ch) Jan Stark LPSC, Grenoble, France (stark@in2p3.fr)Slide2
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…2S. H. Chew Noise in the Readout of ATLAS LAr CalorimetersNoisy channels in the detectors!Slide3
The ATLAS
LAr
Calorimeters
LAr
forward (Fcal
)Tile barrelTile extended barrel LAr electromagnetic barrelLAr electromagnetic end-cap (EMEC)
LAr
hadronic end-cap (HEC)
3
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 absorbersSlide4
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.
4
S. H. Chew Noise in the Readout of ATLAS
LAr
Calorimeters
The bunch crossing time=
25
ns
But, t
he
drift time in the
LAr
gap
~
450 ns
1
2
3Slide5
5
S. 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 NutshellFront-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 signalSlide6
6
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! Slide7
7
S. 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 detector11060 1 116 19 0 0 0 6 3 52 0 974.349 11.2143 013202 1 274 17 0 0 0 7 6 18 0 944.784 30.2519 031093 1 245 60 0 0 0 17 5 117 0 944.236 13.3464 039679 1 63 50 0 0 0 22 2 127 0 983.196 10.7274 047604 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 047606 1 438 42 0 0 0 26 8 118 0 934.462 17.6548 047607 1 439 42 0 0 0 26 8 119 0 951.01 17.2807 061640 1 264 5 0 0 1 2 6 72 0 967.332 21.1794 068987 1 379 13 0 0 1 6 7 123 0 934.017 17.2334 095734 1 310 43 0 0 1 21 6 118 0 965.97 10.401 0113029 1 5 62 0 0 1 31 2 5 0 952.183 14.8943 0145444 1 36 46 2 1 0 19 2 36 0 986.41 10.5099 0153767 1 31 34 3 1 0 24 5 39 0 968.51 11.6612 0178351 1 63 36 4 1 1 14 7 47 0 992.54 11.8433 0184619 1 59 44 4 1 1 18 7 43 0 945.703 14.459 0315531 3 4 29 0 1 0 3 7 11 1 947.216 11.1312 1315570 2 7 31 0 1 0 3 7 50 1 991.372 12.198 1326890 2 2 1 0 1 0 10 6 106 1 949.995 13.4252 1336547 3 6 63 0 1 0 16 7 35 1 992.161 45.2964 1336551 3 6 62 0 1 0 16 7 39 1 973.108 10.9021 1336563 3 7 63 0 1 0 16 7 51 1 1012.84 18.8718 1336655 3 4 52 0 1 0 16 8 15 1 988.347 10.6762 1346250 2 4 37 0 1 0 22 8 10 1 944.161 13.5916 1346266 2 5 37 0 1 0 22 8 26 1 952.744 16.1664 1346302 2 7 36 0 1 0 22 8 62 1 980.425 12.5365 1355842 2 4 8 0 1 1 3 8 2 1 1001.42 16.2463 1The list we obtained for u
nhappy
c
hannels
It agrees well with the list obtained in the meeting!Slide8
So, we wrote another program and obtained the plots.
8
S. H. Chew Noise in the Readout of ATLAS
LAr
CalorimetersTo determine why the channels are unhappy…
ADC countsNumber of eventsNumber of eventsADC countsNumber of eventsADC countstwo humps???Slide9
9
S. 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 countsNumber of samplesThe normal noise signalLook for the noise frequency which has the same pulse pattern…ADC countsNumber of samplesThe abnormal noise signal (from the plot which has two humps)ADC countsNumber of samples10 MHz
ADC counts
Number of samples
30 MHz
ADC counts
Number of samples
19.2 MHzSlide10
Conclusions
We suspected the noise is resulted from the power supply which has a frequency of
~19.2
MHz
.10S. 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…