Radiation Hard Sensors for the Beam Calorimeter of the ILC

C. Grah1, R. Heller1, H. Henschel1, W. Lange1, W. Lohmann1, M. Ohlerich1,3,

R. Schmidt1,3, S. Schuvalow1, K. Afanaciev2, A. Ignatenko2, J. Gajewski4, S. Kulis4, A. Rosca5, Z. Krumshteyn6, A. Sapronov6

N48-4, Thursday, Nov. 1st

1 DESY, Zeuthen, Germany 4 AGH University of Cracow, Poland2 NCPHEP BSU, Minsk, Belarus 5 West University of Timisoar, Romania3 BTU Cottbus, Germany 6 JINR, Dubna, Russia

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Contents

Very forward region of the detectors for the International Linear Collider and the beam calorimeter - BeamCal

Materials under investigationMeasurement of Charge Collection Distance

(CCD) and high dose test beamRadiation hardness of

polycrystalline Chemical Vapor Deposited (CVD) diamonds

GaAssinglecrystalline CVD diamonds

Conclusions

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Very Forward Region of the ILC Detectors

Interaction point

EM calorimeter with sandwich structure: 30 layers of 1 X0

o3.5mm W and 0.3mm sensor Angular coverage from 5mrad to 28 mrad

Purpose:hermetic detector, important for particle searchesoptimize luminosity

LDC

e+e- pairs from beamstrahlung are deflected into the BeamCal

Several MGy per year strongly dependent on the beam and magnetic field configuration

=> Radiation hard sensors, qualified for up to 10 MGy/a

BeamCal

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Materials under Investigation

pCVD diamonds: radiation hardness under

investigation (e.g. LHC pixel detectors)

advantageous properties like: high mobility, low εR = 5.7, thermal conductivity

availability on wafer scale GaAs:

semi-insulating GaAs, doped with Sn and compensated by Cr

produced by the Siberian Institute of Technology

available on (small) wafer scale

sCVD diamonds: available in sizes of

mm2

(courtesy of IAF) Samples from two manufacturers: Element SixTMFraunhofer Institute for Applied Solid-State Physics – IAF

1 x 1 cm2 200-900 μm thick (typical thickness 300μm) Ti(/Pt)/Au metallization

500 µm thick detector, 87 5x5 mm padsMounted on a 0.5 mm PCB with fanoutMetallization is V (30 nm) + Au (1 µm)Works as a solid state ionization chamberstructure is provided by metallization

scCVD diamondarea 5x5 mm2, thickness 340 µm,

metallization Ø3mm

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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 (assuming 36 ionized e-h pairs per μm)

ADC Channels ~ charge

Co

unt

s

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High Dose Irradiation

Irradiation up to several MGy:10 ± 0.015 MeV and beam currents from 10 to 50 nA corresponding to 60 to 300 kGy/h.

Keeping the sensor under bias permanently. This is a much higher dose rate compared to

the application at the ILC (~1 kGy/h)

(1 MGy = 100 Mrad is deposited by about 4 x 1015 e-/cm2)

Superconducting DArmstadt LINear ACceleratorTechnical University of Darmstadt

Beam setupcollimator

preamp box

absorber

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Test Beam Setup

Beam Collimator Sensor Faraday cup

Beam current is measured using the Faraday cup.

Together with correction factors from a GEANT4 simulation we determine the absorbed dose with an error of less than 10%.

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Irradiation of Polycrystalline CVD Diamond

After absorbing 5-6 MGy:

CVD diamonds still operational.

Very low leakage currents (~pA) after the irradiation. Decrease of the charge collection distance. Generation of trapping centers due to irradiation.

pumping

decrease

depumpingby UV

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Comparison to Data from 2006

Results from 2006 have beenconfirmed using lower beam currents.

Very similar behavior of allsamples for high doses.

Keep in mind that the sensorsare continuously in their pumped state during the irradiation.

(Percentage of the maximum CCD)

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Irradiation of GaAs

CCD vs Dose CCD vs HV before and after(500µm thickness)

Irradiated one individual pad of each prototype to about 1 – 1.5 MGy.

Starting at about 50% ofthe sensor thickness.

~ 80% decrease

Ending at about 3 %

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GaAs after Irradiation

Partially irradiated pads show two very distinct signal peaks.High: signal from not irradiated areaLow: signal after ~1.5 MGy

Leakage currents increase byabout a factor of 2...but this timeit is in the μA range.

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Irradiation of Singlecrystalline CVD Diamond

Starts at 100%

Reduction of measured signal, but still operating after 5 MGy.(~340µm thickness)

before irradiation after irradiation

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Summary BeamCal is an important part of the instrumentation of the

very forward region of the ILC detectors. The requirements on the radiation hardness of the BeamCal

sensors are challenging. Up to 10MGy of TID will be accumulated close to the beam.

Diamonds, GaAs and also Si (not covered here) are materials under investigation for this task.

High dose irradiation using 10MeV electrons shows: all CVD diamonds stay functional even after absorbing up to 5

MGy and more. GaAs was irradiated to 1-1.5 MGy. The CCD (efficiency) decreases

and the leakage currents increases to critical levels (without cooling).

poly- and singlecrystalline CVD material show a loss of charge collection, but stay functional with very low leakage currents.

Thanks to: EUDET, the S-Dalinac crew, Norhdia, Worldlab and Intas

http://www-zeuthen.desy.de/ILC/fcal/

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Backup Slides

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Very Forward Region of the ILC Detectors

Interaction point

The purpose of the instrumentation of the very forward region is: Electron veto down to lowest angles supplying a fast luminosity signal to the feedback system of the

accelerator.

EM calorimeter with sandwich structure: 30 layers of 1 X0

o3.5mm W and 0.3mm sensor Angular coverage from 5mrad to 28 mrad Moliére radius RM ≈ 1cm Segmentation between 0.5 and 0.8 x RM

BeamCalLDC

~20 cm

~ 25 cm

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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.

Several MGy per year strongly dependent on the beam and magnetic field configuration

=> radiation hard sensors needed qualified for 10 MGy/a

e- e+

Creation of beamstrahlung at the ILC

≈ 5 MGy/a

e-

e-

γe-

γ

e+

e.g. Breit-Wheeler process

V.Drugakov

6X0Energy deposition and spectrum of shower particles.

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Procedure

Correction factors are obtained from a GEANT4 simulation of the geometry

R = NFC/NSensor ~ 0.96 <Edep>/particle = 5.63 MeV/cm

Apply HV to the DUT

Measure CCD ~20 min

Irradiate the sample~1 hour

During the irradiationthe Faraday cup currentis monitored and used tocalculate the accumulateddose with a total error ofΔD/D < 10%

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CCD Behaviour after Irradiation

Before irradiation

After irradiation before UV illumination

After irradiation, UV illuminated

Value used at testbeam

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Comparison to Earlier Study

strong „pumping“ after irradiation

▪ before irradiation ▪ after irradiation

before/after ~ 7MGy (irradiated in 2006)

After removal of the surface (2.5μm) and remetallization => no change

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Polarization of Single-crystalline CVD Diamond

Observation a)

Signal current and from MIPs decreases.No trapping-detrappingon short timescales

Observation b)

MIP response isdependent on time(after setting HV) and rate

Homogeneous creation of traps+ creation of eh pairs by a MIP pluselectric field leads to polarization.

Measurement at 100V Prediction at 100V

Prediction at 200V

Prediction at 200V (switching HV)

Measurement at 200V (switching HV)

Dose calculationuncorrected!

Dose calculationuncorrected!