Radiation Hard Sensors for the BeamCal of the ILC

Radiation Hard Sensors for the BeamCal of the ILC

C. Grah

FCAL Collaboration

10th ICATPP Conference, Villa Olmo

10.10.2007 C.Grah: Radhard Sensors for BeamCal 2

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


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


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


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


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


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)


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)


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).


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


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


CCD Behavior

CCD is a function of the applied electric field. Saturation at about 1V/µm.


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


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


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


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


Testbeam Setup

Beam Collimator Sensor Faraday Cup


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.


Behaviour after Irradiation

Slight increase of currents forhigher doses.

No significant change of the current-voltage characteristics up to 1.5 MGy.


CCD Behaviour after Irradiation

after 1.5 MGy

~ -30%

~ -80%

after 7 MGy


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


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!


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.


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)


Properties of the GaAs Sensor

Rpad 500 MOhm, pad capacity about 12 pF, dark current 1 μA @ 500 V

CCD = 50% of sensor thickness


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)


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


Radhard Silicon - Before Irradiation

depletion voltage: 336 V → operational voltage 400 V


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


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.


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

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Radiation Hard Sensors for the BeamCal of the ILC

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