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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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 2
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 3
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 4
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 5
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 6
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 7
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 8
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%.
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 9
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 10
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)
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 11
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 %
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 12
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.
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 13
Irradiation of Singlecrystalline CVD Diamond
Starts at 100%
Reduction of measured signal, but still operating after 5 MGy.(~340µm thickness)
before irradiation after irradiation
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 14
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/
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 15
Backup Slides
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 16
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 17
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.
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 18
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%
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 19
CCD Behaviour after Irradiation
Before irradiation
After irradiation before UV illumination
After irradiation, UV illuminated
Value used at testbeam
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 20
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
11/1/2007 C.Grah: Radiation Hard Sensors for BeamCal 21
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!