1. Andrej Gorišek J. Stefan Institute, Ljubljana
ATLAS BCM/BLM Status Commissioning and First Operational Experience of the ATLAS Beam Conditions and Loss Monitors Based on pCVD Diamond Sensors
Andrej Gorišek
J. Stefan Institute, Ljubljana
11th Pisa Meeting on Advanced Detectors
La Biodola, Isola d'Elba (Italy), May , 2009

2. Outline Introduction ATLAS Beam Condition Monitor
principles of operation
commissioning
ATLAS Beam Loss Monitor
design and installation
First measurements with as installed system
BCM with cosmic data
first beam
Luminosity monitoring
ATLAS BCM/BLM Status
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3. The ATLAS BCM collaboration
CERN
B. Demirkoz, D. Dobos, J .Hartert, H. Pernegger, P. Weilhammer
JSI, Ljubljana
V. Cindro, I. Dolenc, A. Gorišek, G.Kramberger, B. Maček, I. Mandić, E. Margan, M. Zavrtanik, M. Mikuž
OSU, Columbus
H. Kagan, S. Smith
Univ. of Applied Science, Wiener Neustadt
E. Griesmayer, H. Frais-Kölbl, M. Niegl
Univ. Toronto
M. Cadabeschi, E. Jankowski, D. Tardif, W. Trischuk
All you ever wanted to know about BCM:
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4. (misfiring of kicker magnet)
Motivation
Experiences (recent at Tevatron) show that beam accidents happen
LHC will store much more energy than ever before (~3000 bunches with 1011 protons of 7 TeV)  about 200-times more energy stored in beams compared to maximum value in previous accelerators like HERA or Tevatron
Potentially dangerous to ATLAS Inner Detector
Time constants of magnets in LHC typically much larger than time of one orbit  can act to prevent beam accidents
20-30 Tevatron turns
(misfiring of kicker magnet)
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5. Beam Accident – Protection
ATLAS is furthest from injection – safest (?)
Passive protection:
ATLAS and CMS have Target Absorber Secondaries (TAS) z=±18m: protecting inner triplet of quadrupoles from secondaries produced in p-p collisions and Inner Detector from beam failures
Active protection:
Beam Interlock System (BIS): two redundant optical loops transporting BeamPermit signals – a logical AND of UserPermit signals provided by user systems (machine beam loss or beam position monitors, experiment Beam Condition Monitors (BCMs), etc.)
If UserPermit is set to False optical loop is interrupted  BeamPermit removed, beam dump procedure initiated (beam is dumped within 3 turns ~270 μs) + no injection from SPS
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6. ATLAS Spectrometer
ATLAS BCM/BLM systems will protect Inner Detector against beam accidents (+luminosity, +trigger,…)
25m
44m
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7. ATLAS Inner Detector BCM
4 BCM detectors installed inside PIXEL volume on each side
z=±1.84 m, r=55 45o
PIXEL
SCT B.
TRT B.
TRT End Cap
SCT End Cap
BCM
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8. BCM – Beam Accidents Protection
Continuous measurement with single MIP sensitivity
Distinguish between interactions and background (scraping of collimators, beam gas,...)  requirement: better than 12.5 ns width+baseline restoration
2 detector stations, symmetric in z
TAS (collimator) event: Δt=2z/c=12.5ns (ideally)‏
Interaction: Δt = 0, 25, … ns
-6ns
6ns
Time difference
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9. pCVD Diamond Material
bunch by bunch measurement  fast signal rise time (1ns), narrow width (2ns), short baseline restoration (10ns)
very close to BP and IP  radiation hardness (50MRad in 10years of ATLAS operation)
pCVD diamond fulfils these requirements (developed in collaboration RD42 – Diamond Detectors Ltd./E6 Ltd.):
high resistivity
low dielectric constant
almost negligible leakage current (room temperature, low noise) – even after irradiation (<100pA)
high charge mobility and ccd of >200m
proven radiation hardness
 talk by H. Kagan on “Diamond Pixel Modules” (Friday afternoon)
REQUIREMENTS
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10. ATLAS Beam Condition Monitor
pCVD sensors of 1x1cm2 and 500m thickness with 8x8mm2 Al finish rad-hard contacts (OSU)
8 detector modules (aluminum oxide base board + 2 pCVD diamond sensors back to back in FE module box)
Fast & short signal (FWHM~2ns, rise time<1ns)‏
Agilent MGA Mhz (gain: 22 dB, NF: 0.9dB)‏
pCVD diamond
Mini Circuits GALI GHz (20 dB)‏
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11. BCM Signal Optimization
double sensor layout – double decker – noise increase of 30% only
45o mounting angle w.r.t. beam axis – increase of signal by 2
most probable MIP energy loss: eo  signal to noise ratios of 10 achievable
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12. BCM Detector modules installed
SLA brackets on PIXEL support structure
BCM Detector module
Beam pipe
Pixel
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13. BCM Readout Chain
analogue signals from BCM detector modules routed behind calorimeter (lower radiation levels – 10Gy in 10 years) where they are digitized by custom board based on ALICE ToT NINO chip
individual BCM detector modules are connected to separate NINO boards for electrical ground separation – minimize interference (grounds connected together close to detector modules)
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14. BCM Readout Chain
rad-tolerant laser diodes transmit signal trough 70m of optical fibers to USA15 counting room
optical signals received and transformed into PECL on two 8 channel optical receiver boards
PECL signal from individual receiver board connected to Read Out Driver (ROD) based on Xilinx Virtex-4 based FPGA board
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15. BCM Data Acquisition
personality modules developed for interfacing input and output signals to RODs
input signal sampled with 2.56 GHz  64 samples of 390ps for each BC (25ns)
connected to ATLAS Central Trigger Processor (CTP), data acquisition (TDAQ), Detector Control System (DCS), Detector Safety System (DSS) and the Controls Interlocks Beam User (CIBU) systems.
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16. Signal analysis - NINO
signals measured in Time-over-Threshold fashion: 25 ps jitter, 1 ns rise time
analogue signals from modules split into two channels of NINO chip in ratio of 1:11 to increase dynamic range of the chip
PH corrections for nonlinearity required (look-up table)
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17. Signal analysis - ROD
cable length differences compensated internally in FPGA
raw data stored in DDR2 memory module for more than the last 1000 LHC turns (circular buffer)
rising edges and pulse widths are reconstructed in signals (at most the first 2 for each BC) and stored in DDR memory module  LHC post mortem  on L1A signal data is formatted and sent over optical link to Read Out Subsystem (ROS)  in time and out of time coincidences: 9 trigger signals to CTP  + high multiplicity  LHC beam abort system and ATLAS DSS
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18. ATLAS Beam Loss Monitor
Recently proposed and built a redundant system to BCM
Simpler – aims only to be a “safety system”
Electronics based on LHC BLM system
pCVD diamond sensors used instead of ionization chambers (similar to CDF at Fermilab)
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19. LHC Beam Loss Monitor
measure and localize beam loses (number of lost particles)
measure particle rates with different integration times (running sums in interval of 40µs to 84s) and act on the basis of them exceeding configurable thresholds
up to 8 ionization chambers read out by “tunnel card”: BLMCFC
converts current into frequency and sends encoded data over optical link to the “surface card”: BLMTC (based on DAB64x card)
connection to the combiner card and trough it
… to BIC
… and beam energy tracker
VME bus:
logging rates
reading out the post-mortem buffer
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20. ATLAS BLM system
8x8mm2 0.5mm thick diamond sensors used (instead of ionization chambers as in LHC)
6 sensors on each side (A and C) installed on IDEP
Modified BLMTC firmware to receive beam dump signals on front panel LEMO outputs  connection to BIC
BLMTC inserted into BCM (standard ATLAS) VME crate
VME bus used for monitoring rates and recording the postmortem buffer
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21. ATLAS BLM detector module
mechanical support:
rad-hard PEEK plastic support
standard double sided PCB – mechanical rigidity and electrical insulation
layers screwed together with M3 screws
sensor:
8x8 mm2 0.5 mm pCVD diamond (by DDL)
metalized at OSU (7.5x7.5 mm2)
assembly:
conductive glue, bonding, soldering
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22. ATLAS BLM Installation
detector mounted to the “Inner Detector End Plate” close to the Beam Pipe
6 detector modules installed on each side
z~3450mm, r~65mm
IDEP
SIDE A
view towards IP
1 A
2 A
4 A
3 A
6 A
5 A
SIDE C
view towards IP
1 C
2 C
4 C
3 C
6 C
5 C
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23. BCM Cosmic data
November 2008 – 1 week of combined Inner Detector cosmic data-taking
Two different triggers:
by Resistive Plate Chamber (RPC) Muon Subsystem and
Transition Radiation Tracker (TRT) Fast OR mechanism
 with combined trigger rate of ~150 Hz
51 M events triggered
131 events with hits reconstructed in BCM
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24. Timing plot preliminary preliminary
each trigger from CTP triggers readout of 31 consecutive BCs
histogram BC of reconstructed hits in BCM
width of distributions – convolution of timing distributions of trigger systems and BCM
both plots show peak around BC=19 as expected
random uniform background
preliminary
preliminary
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25. Channel occupancy preliminary preliminary
channels 0-7 are low gain channels (expect to show signal for ~5 or more MIPs traversing the sensor simultaneously)
NINO thresholds not calibrated  different noise occupancies of readout channels
no hits on C side with TRT Fast OR  also due to known unequal efficiencies of TRT endcaps in the data taking of November 2008 C A
preliminary
preliminary
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26. Track reconstructed
Couple of events show hints that cosmic muon track could have passed trough BCM module
BCM hit reconstructed along with several hits in SCT and TRT tracking systems
TRT
SCT
BCM
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27. First LHC Experience Timing of our RODs was not fully calibrated
Monitor hit rates (integration time of 1 s) transmitted to DCS computer over Ethernet showed increase during the events when beam was splashed into closed collimators
Diamond (erratic) dark currents decrease when sensors are operated in magnetic field  nominal voltage of 1000V is decreased to 800V during magnet off periods
I(A)
time
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28. Luminosity monitoring
Goals of BCM system within the ATLAS Luminosity Working Group:
Monitor instantaneous luminosity
vertex position monitoring
determine dead time
beam separation scans
Counting number of tracks trough BCM modules – monitoring instantaneous luminosity:
BC rate
number of pp in single BC (function of luminosity)
number of tracks per pp
probability of track going to side A
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29. Luminosity monitoring - Simulation
sum of number of tracks per pp collision in BCM
(z,r)-origin distribution of tracks that cross BCM sensor volume
½ of particles from secondaries
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30. Summary
Two pCVD diamond based safety systems Beam Condition Monitor (BCM) and Beam Loss Monitor (BLM) built and being commissioned for ATLAS experiment
First operation experience with BCM obtained throughout last year
BCM has further more ambitious goals (data taking, triggering, luminosity monitoring, beam separation scans,…) while BLM is safety system only
Looking forward to test the fully commissioned systems in the real LHC environment later this year
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