radiation hard sensors for the beamcal of the ilc c. grah fcal collaboration 10 th icatpp...
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Radiation Hard Sensors for the BeamCal of the ILC
C. Grah
FCAL Collaboration
10th ICATPP Conference, Villa Olmo
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Contents
The ILC and the very forward region of the detectors for the International Linear Collider
BeamCal – requirementsRadiation hard materials under
investigation:CVD diamondSiliconGaAs and SiC
Conclusions
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The International Linear Collider ILC
Parameters of the ILC:•e+e- accelerator, sc cavities, gradient 31.5 MV/m => 30km long•CMS energy: 200 to 500 GeV (possible upgrade to 1 TeV)•One interaction region, beam crossing angle of 14mrad and two detectors („push-pull“ scenario) •Peak luminosity: 2 x 1034 cm-2s-1
•typical beam size: (h x v) 650 nm x 5.7nm & beam intensity 2 x 1010 e+e-
~ 30 km
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Very Forward Region of the ILC Detectors
R&D of the detectors in the forward region is done by the FCAL Collaboration. Precise (LumiCal) and fast (BeamCal) luminosity measurement Hermeticity (electron detection at low polar angles) Mask for the inner detectors Not shown here: GamCal, a beamstrahlung photon detector at about 180m
post-IP.
LumiCal
TPC
EC
AL
HCAL
BeamCal
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The Beam Calorimeter - BeamCal
Interaction point
Compact EM calorimeter with sandwich structure:
30 layers of 1 X0
o3.5mm W absorber and 0.3mm radiation hard sensor
Angular coverage from 5mrad to 28 mrad (6.0 > |η| > 4.3) Moliére radius RM ≈ 1cm Segmentation between 0.5 and 0.8 x RM
BeamCalLDC
~10cm
~12cm
Space for electronics
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The Challenges for BeamCal
e+e- pairs from beamstrahlung are deflected into the BeamCal
15000 e+e- per BX
=> 10 – 20 TeV total energy dep.
~ 10 MGy per year strongly dependent on the beam and magnetic field configuration
=> radiation hard sensors
Detect the signature of single high energetic particles on top of the background.
=> high dynamic range/linearity
e- e+
Creation of beamstrahlung at the ILC
≈ 1 MGy/a
≈ 5 MGy/a
e-
e-
γ
e-
γ
e+e.g. Breit-Wheeler process
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Diamond as Sensor Material
Manufacturing of diamond has become more and more available. CVD deposition of polycrystalline diamonds is available at wafer scale (3”-6” diameter)
Properties: Diamond SiliconHardness* 10,000 kg/mm2 1100 kg/mm2
Density 3.52 g/cm3 2.33 g/cm3
Atom density* 1.77 x 1023 1/cm3 0.50 x 1023 1/cm3
Thermal expansion coefficient 1.1 ppm/K 2.6 ppm/KThermal conductivity* 20.0 W/cmK 1.412 W/cmKDielectric strength 10 MV/cm 0.3 MV/cmResistivity 1013 - 1016 Ωcm 2.3 x 105 Ωcm
Electron mobility 2,200 cm2/Vs 1350 cm2/VsHole mobility 1,600 cm2/Vs 480 cm2/VsBandgap 5.45 eV 1.12 eV
Energy/eh-pair 13eV 3.62 eVAv. eh/100μm (MIP) 3600 7800
*highest value of all solid materials(diamond values from Fraunhofer IAF webpage)
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Polycrystalline Chemical Vapour Deposited Diamonds
pCVD diamonds are an interesting material: radiation hardness (e.g.
LHC pixel detectors) advantageous properties
like: high mobility, low εR = 5.7, thermal conductivity
availability on wafer scale Samples from two
manufacturers are under investigation: Element SixTM Fraunhofer Institute for
Applied Solid-State Physics – IAF
1 x 1 cm2 200-900 μm thick
(typical thickness 300μm) Ti(/Pt)/Au metallization
(courtesy of IAF)
(courtesy of IAF)
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IV Characteristics
Typical current-voltage characteristics of a good pCVD diamond.
No breakthrough up to 500V. Very low currents of a few
picoamperes. Symmetric (linear) behavior
(ramping up) Hysteresis observed for all
pCVD samples (ramping down).
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MiP Response of pCVD Diamond
typical spectrum of an E6 sensor
Sr90 source
Preamplifier
Sensor box
Trigger box
&Gate
PA
discr
discr
delay
ADC
Sr90
diamond
Scint. PM1
PM2
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CCD Measurement
~ CCD
CCD = Charge Collection Distance = mean drift distance of the charge carriers = charge collection efficiency x thickness
ADC Channels ~ charge
Co
unt
s
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CCD Behavior
CCD is a function of the applied electric field. Saturation at about 1V/µm.
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Linearity Test at CERN PSHadronic beam, 3 & 5 GeVFast extraction mode ~104-107 particles / ~10 ns
ADCsignal gate
10 ns
17 s
Diamond
Setup
Beam
Scint.+ PMTs.
Response of diamond sensor to beam particles (no preamplifier/attenuated)
Photomultiplier signals
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Response vs. Particle Fluence
30% deviation from a linear response for a particle fluence up to ~106 MIP/cm2
The deviation is at the level of the systematic error of the fluence calibration.
E64 FAP2
Fraunhofer IAFElement Six
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High Dose Irradiation
Irradiation up to several MGy using the injector line of the S-DALINAC:10 ± 0.015 MeV and beam currents from 10 to 100 nA corresponding to about 60 to 600 kGy/h
Superconducting DArmstadt LINear ACceleratorTechnical University of Darmstadt
Energy spectrum ofshower particles in BeamCal
V.Drugakov
6X0
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Preparations and Programme
GEANT4 simulation of the geometry
=> R = NFC/NSensor = 0.98
<Edep>/particle = 5.63 MeV/cm
Beam setup Sample Thickness, µm
Dose, MGy
E6_B2 (E6) 500 >1
DESY 8 (IAF) 300 >1
FAP 5 (IAF) 470 >5
E6_4p (E6) 470 >5
Apply HV to the DUT
Measure CCD ~20
min
Irradiate the sample~1 hour
CCD: Charge Collection Distance
collimator
preamp box
absorber
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Testbeam Setup
Beam Collimator Sensor Faraday Cup
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Results: CCD vs. Dose
100 nA (E6_4p) 100 nA (FAP5)
Silicon starts to degrade at 30 kGy.High leakage currents.Not recoverable.
After absorbing 7MGy:
CVD diamonds still operational.
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Behaviour after Irradiation
Slight increase of currents forhigher doses.
No significant change of the current-voltage characteristics up to 1.5 MGy.
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CCD Behaviour after Irradiation
after 1.5 MGy
~ -30%
~ -80%
after 7 MGy
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After Irradiation: IAF Sample
strong „pumping“ behaviour.
before/after ~ 7MGy
signal recovery after 20 Gy
▪ FAP 5 irradiated, 1st measurement
▪ FAP 5 irradiated, additional 20 Gy
▪ before irradiation ▪ after irradiation
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Monocrystalline CVD Diamond Sensors
sCVD diamondarea: a few mm2, ~thickness 300 µm,
metallization Ø3mm
-25 V
IV Characteristics (too low current for our setup)
100% efficient at low electric fields!
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GaAs Sensor Material
Produced by the Siberian Instituteof Technology, Tomsksemi-insulating GaAs doped by Sn
(shallow donor) compensated by Cr (deep acceptor):to compensate electron trapping centers EL2+ and provide i-type conductivity.
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GaAs Prototype Details
500 µm thick detector, divided into 87 5x5 mm pads
Mounted on a 0.5 mm PCB with fanout
Metallization is V (30 nm) + Au (1 µm)
Works as a solid state ionization chamber and structure is provided by metallization (similar to diamond)
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Properties of the GaAs Sensor
Rpad 500 MOhm, pad capacity about 12 pF, dark current 1 μA @ 500 V
CCD = 50% of sensor thickness
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First View on Testbeam Results
Spatial CCD distribution corresponds to the beam profile
Pad with 2 CCD regions - due to collimation while irradiation → No trap diffusion
Dark current increased up to about 2 μA @ 500 V
beam spot (~1 MGy)
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Radiation Hard Silicon
400 Vreverse voltage
depletion zone
• mCz Si, radiation hard, thickness 380 μm, 5x5 mm2
• n+ on n-configuration• works as solid state ionization chamber, but active volume = depletion zone signal by drifting excess charge carriers• guard rings to avoid surface currents
guard rings
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Radhard Silicon - Before Irradiation
depletion voltage: 336 V → operational voltage 400 V
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Silicon - Under Irradiation
Signal/Noise vs DOSE• Intended as a first step using the radhard silicon• CCD remained constant• Noise increased strongly• No cooling
CCD vs DOSE
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Silicon Carbide SiC is a potential
sensor material with a high bandgap of > 3eV
First SiC material provided by the Technical University of Cottbus (BTU)
~1cm2 size very asymmetric
behavior with high dark currents at low voltages => no signal detectable.
Need material with higher resistivity.
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Summary
The FCAL Collaboration develops the detectors in the very forward region of the ILC detectors.
BeamCal is an important part of the instrumentation.
The requirements on the radiation hardness and linearity of the sensors are challenging.
CVD diamonds, radiation hard silicon, GaAs and SiC are interesting materials for this task and are under investigation.
http://www-zeuthen.desy.de/ILC/fcal/
Cooperation with: SLAC
Stanford University Iowa State University Wayne State University
FCAL CollaborationAim: design and construction of
CollaborationHigh precision design
luminosity detectors
beam monitors
photon detectors
University of Colorado
Brookhaven National Lab NY
Yale University New Haven
Laboratoire de l Accélérateur Linéaire Orsay
Royal Holloway University London
AGH University, Cracow
Institute of Nuclear Physics, Cracow
DESY
Joint Institute Nuclear Research Dubna
National Center of Particle & HEP Minsk
Prague Acad. of Science
VINCA Inst. f. Nuclear Science Belgrade
Tel Aviv University
http://www-zeuthen.desy.de/ILC/fcal/
EUROTeV, EUDET, NoRHDIAINTAS