Firenze, 06 October RD05Lorenzo Bonechi The PAMELA Silicon Tracker Lorenzo Bonechi - PAMELA collaboration INFN Sezione di Firenze - Dipartimento di Fisica dell’Universita’ di Firenze  INTRODUCTION  MAGNETIC SPECTROMETER  PERMANENT MAGNET  SILICON TRACKING SYSTEM  ( MECHANICS )  PERFORMANCES of the tracking system  CONCLUSIONS

Firenze, 06 October RD05Lorenzo Bonechi The PAMELA experiment RESURS DK1 > antiprotons 80 MeV/c GeV/c > positrons 50 MeV/c GeV/c MAIN TOPICS:  antiproton and positron spectra  search for light antinuclei SECONDARY TOPICS:  Modulation of GCRs in the Heliosphere  Solar Energetic Particles (SEP)  Earth Magnetosphere Satellite-borne experiment: Semi-polar orbit  low energy 3-years mission  high statistics PAMELA  Flight model delivered  Launch from Baikonur end 2005 !!!

Firenze, 06 October RD05Lorenzo Bonechi  Earth observation  350 / 610 km  Inclination = 70.4 o  Soyuz 2 launcher  Baikonur Cosmodrome  Launch date = end 2005  3 year mission km Pamela operational During launch / orbital manoeuvres  Housed in an atmospheric pressure vessel  Temperature = 5 o C ÷ 35 o C  All subsystems must withstand launch vibrations!  Electronics must withstand up to ~3 krad Resurs DK1  Total mass ~ 470kg / 345W power budget Satellite and orbit

Firenze, 06 October RD05Lorenzo Bonechi Requirements: MDR = 740 GV (4  m spatial resolution) Spillover limits:  Antiproton up to 190 GeV  Positron up to 270 GeV Magnetic spectromete r  Magnetic rigidity: R = pc/Ze  Charge sign GF ~20.5 cm 2 sr The PAMELA subdetectors

Firenze, 06 October RD05Lorenzo Bonechi  5 magnetic modules  Permanent magnet (Nd-Fe-B alloy) assembled in an aluminum mechanics  Magnetic cavity sizes (132 x 162) mm 2 x 445 mm  Geometric Factor: 20.5 cm 2 sr  Black IR absorbing painting  Magnetic shields MAGNETIC FIELD MEASUREMENTS  Gaussmeter (F.W. Bell) equipped with 3-axis probe mounted on a motorized positioning device (0.1mm precision)  Measurement of the three components in points 5mm apart from each other  Field inside the cavity 0.48 T at the center  Average field along the central axis of the magnetic cavity : 0.43 T  Good uniformity  Measurement of external magnetic field – magnetic momentum < 90 Am 2 The permanent magnet

Firenze, 06 October RD05Lorenzo Bonechi Double Sided (x & y view) Double Metal on the n side (No Kapton Fanout) AC Coupled (No external chips) Produced by Hamamatsu Geometrical Dimensions70.0 x 53.3 mm 2 Thickness300  m Leakage Current< 3  A Decoupling Capacitance> 20 pF/cm Total Defects< 2% p side Implant Pitch25.5  m Readout Pitch51  m Biasing Resistance (FOXFET)> 50 M  Interstrip Capacitance< 10 pF n side Implant Pitch67  m Readout Pitch50  m Biasing Resistance (PolySilicon)> 10 M  Interstrip Capacitance< 20 pF DESCRIPTION of the SILICON SENSORS The silicon tracking system

Firenze, 06 October RD05Lorenzo Bonechi The structure of the tracking system 6 detector planes composed by 3 “ladders”  ladder :- 2 microstrip silicon sensors - 1 “hybrid” with front-end electronics  silicon sensors (Hamamatsu):  300  m, Double Sided - x & y view  Double Metal - No Kapton Fanout  AC Coupled - No external chips  FE electronics: VA1 chip  Low noise charge preamplifier  Operating point set for optimal compromise:  total FE dissipation: 37 W on the channels (6 planes)  Dynamic range up to 10 MIP

Firenze, 06 October RD05Lorenzo Bonechi Request to Hamamatsu: Defects < 2% Defects: Short Circuit of AC coupling (Most common, not destructive) Short between adjacent strips Open circuit on metal lines It seems to be ‘ perfect ’ BUT… The first batch was OK (Prototype ladders were ‘perfect’, bad strip < 2%) We started the mass production… Huge number of bad strips (>10%)!!!!! After a big ‘fight’ we discovered in many sensors short circuits between adjacent strips at the level of implantation (p side). Hamamatsu replaced all the bad sensors (few months of delay) Silicon sensors defects

Firenze, 06 October RD05Lorenzo Bonechi Implantation procedure problems! Transverse ‘cuts’ on the junction side reduce the interstrip resistance

Firenze, 06 October RD05Lorenzo Bonechi Requirements: 1 plane made by 3 ladders no material above/below the plane (1 plane = 0.3% X 0 !!!) survive to the launch phase (7.4 g rms, 50 g shocks!!!) good alignment precision thermal stresses ( C) Solution: Solution: Carbon fibers stiffeners glued laterally to the sensors very high Young module carbon fiber (300 Gpa) pultrusion technology Elastic + Rigid gluing A very thin (2.5  m) Mylar foil is glued on the plane to increase the safety of the whole spectrometer during integration and flight phases No coating on the bonding The mechanical assembly

Firenze, 06 October RD05Lorenzo Bonechi The first silicon plane

Firenze, 06 October RD05Lorenzo Bonechi Mylar film protecting the plane

Firenze, 06 October RD05Lorenzo Bonechi Test plane lodging on the magnet

Firenze, 06 October RD05Lorenzo Bonechi The flight model of the magnetic spectrometer

Firenze, 06 October RD05Lorenzo Bonechi Detector performances (1) Strip noise GOOD = 9.2 GOOD = 4.4 Y view X view MIP signal 50 GeV/c proton (CERN-SPS 2003)

Firenze, 06 October RD05Lorenzo Bonechi  x = (2.77 ± 0.04)  m  y = (13.1 ± 0.2)  m GeV pions (CERN-SPS 2000) beam-test of a small tracking- system prototype Spatial resolution Simulation of silicon detector: best p.f.a.  angle-dependent non- linear ETA algorythm (n=number of used strips) ETA2 ETA3 ETA 4 ETA2 Detector performances (2)

Firenze, 06 October RD05Lorenzo Bonechi Momentum resolution 2003  Last beam-test of PAMELA flight CERN-SPS MDR ~ 1 TV Multiple scattering N x &  x Track selection cuts:  Nx  5 Ny  4  Hit views 1x and 6x  95%-efficiency cut on  GeV/c protons

Firenze, 06 October RD05Lorenzo Bonechi On-ground muon results 2005  acquisition of atmospheric particles during PAMELA test before delivering  Check of spectrometer systematics with positive and negative muons Very preliminary results: - no efficiency correction - first-order alignment - no ETA p.f.a. Very preliminary! Very preliminary!

Firenze, 06 October RD05Lorenzo Bonechi PAMELA apparatus integrated and delivered to the Russian space agency  PAMELA apparatus integrated and delivered to the Russian space agency  launch foreseen for the end of 2005  Detectors tested with particle beams and atmospheric muons during integration phase Spectrometer:   x ~3  m at 0 o,  x < 4  m up to 10 o  MDR up to 1 TV  The spectrometer meets the requirements for the PAMELA mission Conclusions

Firenze, 06 October RD05Lorenzo Bonechi

Firenze, 06 October RD05Lorenzo Bonechi The PAMELA experiment fluxes measurement Search for light Antinuclei Modulation of GCR’s in the Heliosphere Solar Energetic Particles (SEP) Earth Magnetosphere … spectra 80 MeV/c … 190 GeV/c spectra 80 MeV/c … 190 GeV/c e + spectra 50 MeV/c … 270 GeV/c MAIN TOPICS: SECONDARY TOPICS: Antiproton flux Positron charge ratio

Firenze, 06 October RD05Lorenzo Bonechi Orbit development

Firenze, 06 October RD05Lorenzo Bonechi ParticleNumber (3 yrs)Energy Range Protons MeV – 700 GeV Antiprotons> MeV – 190 GeV Electrons MeV – 2 TeV Positrons> MeV – 270 GeV He MeV/n – 700 GeV/n Be MeV/n – 700 GeV/n C MeV/n – 700 GeV/n Antihelium Limit MeV/n – 30 GeV/n ‘Semi-Polar’ orbit (70 0 )  Low energy particles Wide energy range + 3 years mission  Reliable measurements Expected Fluxes in 3 Years

Firenze, 06 October RD05Lorenzo Bonechi TRD Threshold device. Signal from e ±, no signal from p,  p 9 planes of Xe/Co 2 filled straws (4mm diameter). Interspersed with carbon fibre radiators  crude tracking. Aim: factor 20 rejection e/p (above 1GeV/c) ( with calorimeter) Si Tracker + magnet Measures rigidity 5 Nd-B-Fe magnet segments (0.4T) 6 planes of 300  m thick Si detectors ~3  m resolution in bending view demonstrated, ie: MDR = 740GV/c +/-10 MIP dynamic range Time-of-flight Trigger / detects albedos / particle identification (up to 1 GeV/c) / dE/dx Plastic scintillator + PMT Timing resolution = 120ps Si-W Calorimeter Measures energies of e ±.  E/E = 15% / E 1/2 + 5% Si-X / W / Si-Y structure. 22 Si / 21 W  16X 0 / Imaging: EM - vs- hadronic discrimination,longitudinal and transverse shower profile Anticoincidence system Defines acceptance for tracker Plastic scintillator + PMT Pamela Subdetectors Acceptance ~20.5 cm 2 sr 1.2 m Mass ~450 kg Pamela Subdetectors

Firenze, 06 October RD05Lorenzo Bonechi The PAMELA Magnetic Spectrometer Magnetic SystemMagnetic System –It produces an intense magnetic field region where charged particles follow curved trajectories Tracking SystemTracking System –It allows to determine six points in the high field region to reconstruct the particle trajectory and so its momentum and charge sign e+e+e+e+B Momentum p   m   v Charge sign ( e + /e - ) ( p/p )  If B uniform and perpendicular to p, then

Firenze, 06 October RD05Lorenzo Bonechi A glossary of magnetic spectrometers for cosmic rays studies e+e+e+e+ B Momentum p = qBr (r=radius of curvature) Rigidity R = p/q = Br Deflection  = 1/R = q/p  R/R =  = R  (  = constant  point’s measurement error) Maximum Detectable Rigidity (MDR) : spatial resolution

Firenze, 06 October RD05Lorenzo Bonechi 5 magnetic modules permanent magnet assembled in an aluminum mechanics –Nd-Fe-B –Nd-Fe-B alloy magnetic cavity sizes: –(132 x 162) mm 2 x 445 mm field inside the cavity: –0.48 T –0.48 T at the center places for detector planes and electronics boards lodging 20.5 cm 2 srGeometric Factor: 20.5 cm 2 sr Black IR absorbing painting (not shown in the picture!) MAGNETIC SYSTEM The PAMELA Magnetic Spectrometer Geometry of a magnetic block Permanent magnet elements Aluminum frame Magnetic Tower The “Magnetic Tower” Base Plate prototype

Firenze, 06 October RD05Lorenzo Bonechi The PAMELA Magnetic System Magnetic field measurement Gaussmeter F.W. Bell equipped with 3-axis probe mounted on a motorized positioning device (0.1mm precision) 67367Measurement of the three components in points 5mm apart from each other 0.43 TAverage field along the central axis of the magnetic cavity: 0.43 T Good uniformity !Good uniformity ! Main field component along the cavity axis Main field component for z=0 (I) Main field component for z=0 (II)

Firenze, 06 October RD05Lorenzo Bonechi The PAMELA Tracking System 6 detector planes each plane: composed by 3 “ladders” the “ladder”: 2 microstrip silicon sensors + 1 hybrid circuit with front-end electronics (VA1 chip) silicon sensors: double sided; double metalization; integrated decoupling capacitance resolutions: 740 (GV/c)MDR > 740 (GV/c) The TRACKER Thedetector planes The detector planes The“ladder” The “ladder” Thesilicon sensor The silicon sensor

Firenze, 06 October RD05Lorenzo Bonechi Requirements: Very small power consumption (60 W all included for readout channels) Very low noise (3  m resolution required!!!!) Redundancy and safety (satellite experiment) Protection against highly ionizing cosmic rays (Mainly Single Event Effect tests) Very big data reduction (4 GB/day of telemetry, 5 Hz trigger rate, 30 GB/day of data, >90% reduction is mandatory) Solutions: CMOS low power analog and digital electronics VA1 chips: ENC = 185 e e -  C(pF) Small input Capacitance (<20pF) Decoupling between front-end and read-out Big modularity, hot/cold critical parts Selection of components (dedicated tests) Limiting circuits on the power lines Architectural `tricks’ (error correction codes, majority logic etc.) 12 dedicated DSP (ADSP2187) with highly efficient compression alghoritm Few words on the electronics….

Firenze, 06 October RD05Lorenzo Bonechi The silicon tracker front-end 1.2 µm CMOS (6.2 · 4.5 mm2 chip area); ±2 V power rails; low-noise charge preamplifier; operating point set for optimal compromise: VA1 chip - total VA1 dissipation: 37 W; - output saturation at ~ 10 MIP (MIP release 4.6 fC in 300 µm Si).

Firenze, 06 October RD05Lorenzo Bonechi MAGNETIC FIELD MEASUREMENTS  Test were done in the following conditions:  Mechanical aluminum frames with iron replacing the magnet;  Different paints;  System closed in a vacuum chamber to avoid air convection;  Tracker planes replaced by mechanical planes (mechanical silicon + raw alumina) with the front-end electronics replaced by resistors;  Several PT1000 temperature sensors glued on the plane and on the iron blocks. Tracker front-end: thermal test

Firenze, 06 October RD05Lorenzo Bonechi Silicon gluing points Siliconic glue

Firenze, 06 October RD05Lorenzo Bonechi First resonance frequency: 340 Hz!!!! Test plane survived to +6db spectrum (10.4 g rms) and repeated 50 g/5 ms + 40g/1 ms shocks Vibrations tests in Galileo (Florence)

Firenze, 06 October RD05Lorenzo Bonechi On 2000 Beam Tests:94.6% compression factor no loss of resolution no loss of efficiency 3.3 kB/event (tracker) No Zero Suppression (Losses of particles in case of bad strips or change in the pedestals!!!) We use a reversible alghoritm (Zero Order Predictor, ZOP)  event strip  ADC event strip - PED strip - CN event  event strip  is distributed around 0 First word is transmitted Following word is transmitted if above/below n   A word is transmitted with the corresponding address if the preceding one was not transmitted If a cluster is identified (  event strip > N  )  +/- 2 strips are transmitted ZOP compression algorithm

Firenze, 06 October RD05Lorenzo Bonechi Compression time<1ms Compression factor>96% First Plane Last Plane Decompressed data o Non compressed data Signal/Noise Decompressed data o Non compressed data Resolution  x (  m) Some results on the compression…

Firenze, 06 October RD05Lorenzo Bonechi 2002: production of flight model detector planes Performances obtained with cosmic rays in Firenze : s/n for MIP

Firenze, 06 October RD05Lorenzo Bonechi July 2000: CERN SPS Spatial resolution (July 2000 beam test with 5 ladder prototype MS) FINAL LADDERS FINAL ELECTRONICS SMALLER MAGNETIC SYSTEM  DISTRIBUTION  R  q  p  p/p versus p

Firenze, 06 October RD05Lorenzo BonechiSignal non bending view bending viewSignal/Noise s/n  26 s/n  GeV/c Electron event non bending view bending view During the last test (June 2002) the spectrometer flight model has been tested to determine the performances July 2002: CERN SPS