Giovanni De Lellis

University of Naples (Italy)

An overview of the European Scanning System (ESS)

Nucl.Instrum.Meth. A568 (2006) 578-587 Nucl.Instrum.Meth. A554 (2005) 247-254 Nucl.Instrum.Meth. A551 (2005) 261-270

Working principles

• High speed computer-controlled precision mechanics for both horizontal and vertical stages, able to move from one field of view to the next in less than 0.1 s

• Standard optical system customized to analyze 300 µm thick emulsion films

• Mega pixel camera interfaced with a high speed frame grabber and a vision processor grabbing and analyzing images at 350 fps

An European R&D project started in 2000 ended with the

first prototype in Summer 2004, achieving 20cm2/hour

Bari, Bern, Bologna, Lyon, Naples, Neuchatel, Rome,

Salerno

Mechanical movementsF

ield

of

view

Time evolution of the stage positionduring the field of view change

Measurement of the time needed for the field of view change

dumping the vibration within 0.2µm

Movement cycle• Goal of 20 cm2/hour • One field of view of 390 x 310 µm2 1cm2 ~ 827 views

4.6 views/s• 1 view to be scanned within 217 ms• 10% contingency (overlapping of neighboring views)

f.o.v change < 190 ms

X and Z movements during 2 datacycles. A cycle of 170 ms achieved

Optical system

• Objective: 50x Nikon immersion oil with N.A. 0.9 and W.D. 400 µm• Illumination system below the table developed jointly with the Nikon-

Italy: tungsten halogen lamp with computer controlled power supply• image of the lamp filament focused on the aperture diaphragm of a

condenser which concentrates the light into a cone illuminating the emulsion sheets

• Mikrotron CMOS camera: 1280 x 1024 pixel images at up to 500 fps• 377 fps and 8-bit gray level images lead to 471 MB/s

Software• Improvements in terms of speed obtained by an asynchronous data-

taking scheme: parallel execution of several tasks• Execution proceeds along 4 independent steps, synchronized at the end

of each cycle• A) move the optical system along the vertical axis during the grabbing;

at the end of the image taking, it resets the Z position and move X and Y to the next field of view (stop and go)

• B) acquire images through the frame grabber• C) image processing • D) loads the processed image of the previous field of view and performs

cluster and track recognition

Measurements

Base-track to micro-track slope difference for perpendicular (left) and 400 mrad inclined tracks (right)

Base-track angular and position accuracy as a function of the angle (10 GeV - beam at CERN)

Emulsion and base thickness Cluster profile after a smoothing procedure

Derivative of the cluster profile

flat distribution except at the edges

(maximum and minimum)

mean values computed over a 3 region around maximum and minimum emulsion edges

relative accuracy of ~ 0.2%

Correction especially effective on large angle tracks

µm µm

µm

Position and angular accuracy

X projection Y projection

0.05 µm

Straight tracks (up to 50 mrad)

Median ~ 0.4 mrad

200 mrad inclined tracks

0.6 mrad

300 mrad inclined tracks

0.9 mrad

Residual of base tracks w.r.t. fitted tracks

Nucl. Instrum. Meth. A554 (2005) 247

Conclusions• The ESS working since 2004 when the first

prototype was developed

• The system is capable of scanning 20cm2/hour with a routine accuracy of 2 mrad in angle

• About 15 systems operative in Europe

• A similar system devoted to precision measurements is also available

• Currently scanning OPERA and PEANUT films