The ATLAS Beam Conditions Monitor

The ATLAS Beam Conditions Monitor

Marko MikužUniversity of Ljubljana & Jožef Stefan Institute

IEEE NSS’07 N31-7

Hawaii, October 31, 2007

NSS’07, Hawaii, Oct 31, 2007 ATLAS BCM (M.Mikuž, Ljubljana) 2

The ATLAS BCM collaboration

• CERN D. Dabos, H. Pernegger, P. Weilhammer

• Fotec & Univ. Wiener Neustadt E. Griesmayer, H. Frais-Kölbl, M. Niegl

• JSI & Univ. 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. Toronto M. Cadabeschi, D. Tardif, W. Trischuk

~20 people from 5 institutes


Aim of the ATLAS BCM

• Goal of the BCM detector system inside the ATLAS Inner Detector:

Monitor instantaneous background rate and collision rate during normal running

• Measure background rate close to vertex• Compare to rate of collisions and provide basic bunch-by-bunch

luminosity measurement

Protection in case of larger beam losses• Detect early signs of beam instabilities (e.g. wrong magnet settings,

trips,…)• Issue warning and alarm signals for equipment protection• Input to ATLAS Detector Safety system and LHC beam abort


Timing of background vs. interactions• Distinguish collisions from background through time-of-flight measurement with detectors at either side of

the IP Is measured for every bunch crossing (25ns) Requires fast and radiation hard detector + electronics ( rise time ~ 1ns, pulse width ~ 3ns, baseline restoration < 10ns) Out of collision time hits signatures of beam anomalies

Time difference

Interactions: t = 0, 25, … ns Upstream background: t = 2z/c = 12ns

BCM Side A - Side C


The Beam Conditions Monitor

• 4 BCM stations on each side of the Pixel detector Mounted on Pixel support structure at z

= +/- 183.8 cm and r = 5.5 cm Each station: 1 cm2 detector element +

front-end analogue readout

183cm

38 cm


The BCM is installed in ATLAS

• BCM installed on Pixel detector, lowered into ATLAS pit in June 2007


The BCM Module

• Sensors are poly-crystalline CVD diamonds Developed by RD42 and Element Six Ltd

• Radiation hard Shown to withstand > 1015 p/cm2

• Fast & short signal (FWHM~2ns, rise time<1ns) Large charge carrier drift velocity (107 cm/s)

(operates at high drift field ~2 V/m)

• Very low leakage current after irradiation Does not require detector cooling

2 diamonds each with:Thickness 500 mCCD @1V/m ~ 200mSize: 10 x 10 mm2

Contact size: 8 x 8 mm2

BCM operation: 2 V/m


Front-end readout: RF amplifier

• 2-stage amplification of ionization current pulse RF amplifier, no feed-back

• Parameters Bandwidth 500 MHz (1st stage) Amplification ~40 dB

• Radiation hard to ~1015 n/cm2

Tested at Ljubljana TRIGA reactor and CERN PS Find gain reduction of 20% after 5x1014 n/cm2 plus 5x1014 p/cm2 at constant

noise


BCM system overview

Inside Pixel Package At PP2 (~1st muon chamber) Counting room USA15

~30 Mraddetector

~1 kradTOT “digitization”


Functional tests of BCM chain

• BCM modules and performance of the signal processing chain have been tested in several lab tests and test beams

• We currently use beam tests to commission the readout electronics using three spare modules

• The next slides will show an overview of the tests done: Module tests during production Analogue signal response during beam tests Performance after analogue-to-digital conversion and optical link Efficiency & Noise Timing resolution


Module tests• Diamonds

IV curve & CCD measurements before assembly to modules

• Use 90Sr source test setup to characterize each module Measure signal distribution and noise in HV scan from -1000V to +1000V Done before and after burn-in (80°C@12hrs) and thermal cycling (10 cycles -20 to

+40°C) while modules are operated

• Measure on modules a most probable SNR = (7.3 ± 0.56) :1 for 90° impact Meets our requirement of 10:1 in final configuration at 45° ( x √2)

Smp ~ 2.7mVNoise rms~330 V

200 MHz BWL


Test beam (CERN SPS)

• Test BCM modules in high energy pion beam at CERN SPS

• Goal: Evaluate analogue signals Test NINO time-over-threshold

(TOT) conversion and opto-link Measure efficiency, noise rate and

timing resolution Test V1.0 of FPGA readout board

• Setup: Telescope with 5 scintillators and

2x2 mm2 trigger area, BCM modules moved across beam

BCM stations connected via 16 m coax cable to Ortec 300 MHz amplifier for analogue measurements and VME 2 Gs/s ADC

BCM stations connected via 16 m coaxial cable to NINO board + opto transmitter + fibre + opto receiver going to VME readout and FPGA readout


Signal uniformity & time resolution

• Efficiency versus beam position Analogue signal > 150 ADC counts Scans in steps of 1x1 mm2

• Exhibits very efficient and uniform response over active area

• Time difference of NINO outputs between 2 BCM stations NINO threshold fixed to 200 mV

• Easily meets requirement of 1 ns

NINOTime res ~ 490ps

No tails !

Effi

cie

ncy


Time resolution

• Time difference between 2 BCM stations

• Two measurement sets: Offline analysis of analogue signals assuming a start time at 50% amplitude

(“constant-fraction-discriminator”) Time resolution of NINO output with fixed threshold in NINO operational

range (200mV)

AnalogTime res ~ 360ps

NINOTime res ~ 490ps

No tails !


Efficiency and noise rate • Efficiency and noise rate measured after analogue-to-digital

conversion with NINO and optical link

Median signal 335mV onNINO discriminator

Slope = 31mV rms noise *

* Baseline noise of NINO without input connected = 13.5mV rms

• Efficiency >99% for threshold of 180mV or less

• Median SNR after full signal chain ~ 11:1

Beam blocker IN

Muons “leaking” through beam blocker

Machine development – lower muon rate


Operation in ATLAS

• For operation want to maximize efficiency at minimal number of noise hits per LHC BX (25 ns)

• Threshold optimized with efficiency versus noise occupancy per module and BX: Horizontal axis is calculated from fit to previous noise vs threshold plot

e.g. 180 mV threshold:

Efficiency is 99% atnoise occupancy of 3 x 10-8 /module/BX

At low luminosity (5x1032 cm-2s-1) expect ~13% of BX’s have Side A-C coincidence


Radiation test of complete module

• Radiation hardness of sensors, electronics and components verified separately up to level of 1015 cm-2 (30 MRad)

• Want to assess performance of complete module

• Irradiation/test of one module Test in beam – June 07 Irradiate to 1014 p/cm2 – July 07 Test in beam – August 07 Irradiate to 3x1014 p/cm2 – September 07 Test in beam – now Irradiate to 1015 p/cm2 – Spring 08 Test in beam – Summer 08

non-irradiated

1014 p/cm2

• ~20 % of signal loss observed in test beam after 1014 p/cm2

Diamonds not properly pumped – need to cover complete sensor

Loss consistent with that of samples irradiated to same fluence with neutrons – see talk N44-5 tomorrow

Expect complete signal recovery after pumping Tests with module irradiated to 3x1014 p/cm2 ongoing


Summary

• ATLAS BCM will monitor beam conditions close to the IP in ATLAS using a time-of-flight measurement

• Based on pCVD diamonds readout by fast RF amplifiers to achieve very fast signal response and required radiation hardness Rise time 1.3ns & ~2ns FWHM pulse width

• We have tested the full set of BCM modules in beam tests demonstrating the required performance Efficiency of ~99% at operational threshold with noise occupancy

/module/BX <10-7

Time resolution ~500ps

• All BCM modules were installed in ATLAS together with the ATLAS Pixel detector in June 2007


Backup slides …


LHC beam losses

• E.g. wrong magnet settings or trips can lead to beam scraping on collimators Simulations of beam orbits with wrong magnet settings near ATLAS IP (D. Bocian

Accidental Beam Losses during Injection in the Interaction Region IR1 Dariusz Bocian / EST-LEA and ATLAS)

• Time constants of failures (trips ,…) are often large (~ms)

• If signs are detected early, the beam can be aborted


Signal optimization• Step 1: 2 Diamonds read out in parallel increase signal by factor 2, noise

increases only by ~30%

• Step 2: Place at 45 degrees -> 2 signal increase, no noise increase

• Step 3: Adding ~200-300MHz BWL on NINO input improves SNR by 30% (timing resolution worsens by ~ 10%)

• Step 4: operate at 2V/m instead of 1V/m -> increases signal by up to 50%

amplitude noise

SNR

no BWL

200MHz BWL

RMS=0.66mV

RMS=0.33mV

MP=3.7mV

MP=2.5mV


Analogue response in test beam

• Single event and signal distribution

• <Signal rise time>=1.3 ns and <FWHM pulse width> = 2.1 ns

• Signal and noise well separated


5 x 1032

2.8 x 1034

1 x 1034

Number of BCM hits & coincidences

• Number of BCM station hits/BCO At low luminosity

expect ~ 50% of BCO have >= 1 hit

• Coincidences Plots as # Side A * #

Side C At low luminosity

expect ~13% of BCM have a coincidence

No timing cut


Radiation Test results

• Measure response of irradiated 1st stage after full irradiation with Si-diode and 90Sr source

• Noise constant

• Overall gain reduction of ~ 20% after full irradiation


LHC Beam loss scenario

• Simulation by CMS: single proton lost on collimator (“TAS”)

(dose [Gy])

(M. Huhtinen, LHC Machine Protection WG, Oct. 2003)

~ MIPs/cm2 per proton


Passive signal summation

• Increase signal by using 2 diamonds acting as one current source (“Double diamond assembly”) 2 independent current signals summed at input

signal

HV drift voltage


FPGA backend

Have developed the V1.0 signal processing code

Rocket I/O acquisition of BCM signals from optical board (2.6 GHz sampling)

Edge detection, pulse width calculation

DDR2 circular buffers Ethernet + Client Software on

PC In-time/out-of-time

coincidences

Tested in most recent beam tests with full signal chain and two BCM stations

Data analysis is ongoing Plan second run with FPGA

end October in SPS testbeam


BCM simulations

• Simulations in full ATHENA framework

• Average number of tracks in BCM diamonds per p-p collision: 0.375

• Surprise: half of events from decays and scattering in material

• Studies of coincidences to establish FPGA algorithms ongoing

BCM

Pixels

Beam pipeDecays


BCM simulations – movement of vertex

• Explored sensitivity of BCM rates to vertex displacements• Vertex displaced to z = +10 cm• Surprise: more BCM hits on side C – secondaries dominate• dPA/dz = (-0.11 ± 0.05) m-1, effect at % level (• dPA/dz = +0.12 m-1 for primaries only

Vertex at z=0 Vertex at z=+10

More material towards Side C

The ATLAS Beam Conditions Monitor

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