The ATLAS The ATLAS BBeam eam CConditionsonditions MMonitoronitor

The ATLAS The ATLAS BBeam eam CConditionsonditions MMonitoronitor

AbstractThe ATLAS Beam Conditions Monitor is being developed as a stand-alone device allowing to separate LHC collisions from background events induced either on beam gas or by beam accidents, for example scraping at the collimators upstream the spectrometer. This separation can be achieved by timing coincidences between two stations placed symmetric around the interaction point. The 25 ns repetition of collisions poses very stringent requirements on the timing resolution. The optimum separation between collision and background events is just 12.5 ns implying a distance of 3.8 m between the two stations. 3 ns wide pulses are required with 1 ns rise time and baseline restoration in 10 ns. Combined with the radiation field of 1015 n/cm2 in 10 years of LHC operation only diamond detectors are considered suitable for this task. pCVD diamond pad detectors of 1 cm2 and around 500 μm thickness were assembled with a two-stage RF current amplifier and tested in proton beam at MGH, Boston and SPS pion beam at CERN. To increase the S/N ratio two back-to-back diamonds were read out by a single amplifier and the detectors inclined to 45 degrees. Limiting the bandwidth at the readout to 200 MHz provided further improvement; S/N ratio of nearly 10:1 could be achieved with MIP's. Amplifiers of the two stages were irradiated with protons and neutrons to 1015 n/cm2. Evaluating the irradiated electronics with silicon pad diodes, 20 % degradation in S/N ratio was observed. Ten detector modules are being assembled and tested at CERN for their final installation into the ATLAS pixel support structure in the beginning of 2006.

M. Mikuž1, V. Cindro1, I. Dolenc1, H. Kagan5, G. Kramberger1, H. Frais-Kölbl4, A. Gorišek2, E. Griesmayer4, I. Mandić1, H. Pernegger2, W. Trischuk3, P. Weilhammer2, M. Zavrtanik1

1Univ. Ljubljana / Jožef Stefan Institute, Ljubljana, Slovenia, 2CERN, Geneva, Switzerland, 3University of Toronto, Toronto, Canada, 4Fotec, Wiener Neustadt, Austria, 5Ohio State University, Columbus, USA

Motivation Provide distinctive signature of beam anomalies in ATLAS

such as Beam scraping at TAS collimators Beam gas interactions

Stand alone device providing information about genuine interactions Monitoring of interactions at LHC start-up Luminosity assessment

Requirements Fast signals

Rise-time ~ 1 ns Width ~ 3ns Base line restoration in ~ 10 ns to prevent pile-up

Single MIP sensitivity S/N ~ 10 for MIP before irradiation

Installation close to beam pipe at large η Radiation hardness up to 50 MRad and 1015 π/cm2

No maintenance scenario – robust detector

Working principle Distinguish interactions from background via time of flight With two symmetric stations at ±Δz/2

Interactions: in time Background: out of time by Δt = Δz/c

At high luminosity expect hits for each bunch crossing (BX) Interactions at Δt = 0, 25, 50 … ns Optimally background at Δt = 12.5 ns ⇒ Δz = 3.8 m

X

2 detector stations, symmetric in z

TAS events: t = 0, 2z/c; Δt=2z/c

Interactions: Δt = 0, 25, … ns

Δ

Sensors pCVD diamond sensors chosen

Radiation hard – shown to work at > 1015 π/cm2

Fast signals – high velocity and cut-off due to trapping Small leakage current – no cooling required

Procurement in collaboration with CERN RD-42 Sensors produced and conditioned by Element Six Ltd. Metallized with proprietary radiation hard process at

OSU Sensor properties

Size 10 mm x10 mm, active 8 mm x 8 mm (metallization) Thickness ~500 μm Charge collection distance ~220 μm Holds ~ 2 V/ μm, operating voltage 1000 V, current ~ 30

pA

Sensor assembly – two sensors back-to-back at 45° to increase signal

183cm

38 cm

ATLAS

44 m

Pixel

BCM

BCMmodules

Realization Two stations with four detector modules each

Mounted on pixel support structure at z = ±183.8 cm Sensor at r ~ 55 mm, about 20 mm from beam pipe

Sensor with Autest metallization

Sensor inmodule box

MIP

Back-to-back diamonds at 45°

Front-end electronics Two stage Fotec HFK500 amplifier

1st stage: 500 MHz Agilent MGA-62563 GaAs MMIC low noise amplifier (A = 22 dB, NF = 0.9 dB)

2nd stage: Mini Circuits Gali-52 InGaP HBT broad-band micro-wave amplifier (A = 20 dB)

Amplifiers tested for radiation hardness Up to 1015/cm2 reactor neutrons and protons from CERN

PS Agilent: ~ 20 % amplification loss observed with Si

diodes, no noise increase Gali-52: 0.5 dB amplification loss FE amplifier OK for BCM application

Amplifier schematic

1st 2nd stage

Amplifier in module box

Si diode signal Si diode noise Gali-52 amplification

Non-irradiated/irradiated Agilent FE comparison

BCM modules Fe amplifier and sensor in module box

RF design Sensors mounted back to back on ceramics Amplifiers ~10 cm from sensor to reduce radiation dose

Mounted on pixel support tube in a bracket at 45°

η range of BCM compared to other luminosity monitors in ATLAS

The total of 10 BCM module boxes ready to be equipped with sensors

BCM module equipped with sensors

BCM module boxin prototype bracket

BCM module tests Beam test at MGH Boston

Proton beam 200 MeV and 125 MeV Signal ≥ 2.3 MIPs Single and back-to-back sensors at 0 and 45° Signal increase 0->45° by ~ √2 Signal increase in double-decker by 2, noise by 1.3

Beam test at CERN SPS SPS H8 pion beam – MIPs signal with 16 m of cable: S/N (most probable) ~ 7.5:1 Timing: difference between two stations 2.7 ns FWHM Improved to 9.2:1 by implementing 200 MHz BWL on

scope

Bench tests at CERN 30 MBq 90Sr source; ~ MIPs signal QA for BCM modules Module stability tests Noise independent of HV Good reproducibility of signals Signal stable to 4 % during 24 h, longer tests running

NINO amplifier-discriminator tests Differential timing amplifier-discriminator (1 ns peak, 25

ns jitter) LVDS output with width proportional to time-over-

threshold Radiation tolerant design by CERN-MIC Signal split 1:12 into two inputs to increase dynamic

range Tests confirm suitability as BCM back-end chip

Back-to-back Single diamond

0°

45°single double

Beam-test set-up at MGH Boston

Fotec FE (500 MHz) 200 MHz BWL

S/N ~ 7.5:1 S/N ~ 9.2:1

Typical MIP pulse

30 MBq 90Sr sourceBCM module box

Scintillator & PMT

Source QA set-up at CERN

FE output

NINO output

Amplitude

Pulse-width

NINO time-over-threshold functionalityNINO count-rate vs. threshold

for noise / signal & noise

~30 MRad

~100 kRad

ATLAS PIXEL

ATLAS PP2electronics

cavern

Signal processing schematics

~15 m

~100 m

Signal Noise