1. Radiation Hard Sensors for the Beam Calorimeter of the ILC C. Grah 1, R. Heller 1, H. Henschel 1, W. Lange 1, W. Lohmann 1, M. Ohlerich 1,3, R. Schmidt 1,3, S. Schuvalow 1, K. Afanaciev 2, A. Ignatenko 2, J. Gajewski 4, S. Kulis 4, A. Rosca 5, Z. Krumshteyn 6, A. Sapronov 6 N48-4, Thursday, Nov. 1 st 1 DESY, Zeuthen, Germany 4 AGH University of Cracow, Poland 2 NCPHEP BSU, Minsk, Belarus 5 West University of Timisoar, Romania 3 BTU Cottbus, Germany 6 JINR, Dubna, Russia

2. 11/1/2007C.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 investigation  Measurement of Charge Collection Distance (CCD) and high dose test beam  Radiation hardness of  polycrystalline Chemical Vapor Deposited (CVD) diamonds  GaAs  singlecrystalline CVD diamonds  Conclusions

3. 11/1/2007C.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 X 0 o3.5mm W and 0.3mm sensor  Angular coverage from 5mrad to 28 mrad  Purpose:  hermetic detector, important for particle searches  optimize 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

4. 11/1/2007C.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 ε R = 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 mm 2 (courtesy of IAF)  Samples from two manufacturers:  Element Six TM  Fraunhofer Institute for Applied Solid-State Physics – IAF  1 x 1 cm 2  200-900 μm thick (typical thickness 300μm)  Ti(/Pt)/Au metallization  500 µm thick detector, 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  structure is provided by metallization  scCVD diamond  area 5x5 mm2, thickness 340 µm,  metallization Ø3mm

5. 11/1/2007C.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 delay ADC Sr 90 diamond Scint. PM1 PM2

6. 11/1/2007C.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 Counts

7. 11/1/2007C.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 10 15 e -/ cm 2 ) Superconducting DArmstadt LINear ACcelerator Technical University of Darmstadt Beam setup collimator preamp box absorber

8. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 8 Test Beam Setup BeamCollimatorSensorFaraday 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%.

9. 11/1/2007C.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 depumping by UV

10. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 10 Comparison to Data from 2006 Results from 2006 have been confirmed using lower beam currents. Very similar behavior of all samples for high doses. Keep in mind that the sensors are continuously in their pumped state during the irradiation. (Percentage of the maximum CCD)

11. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 11 Irradiation of GaAs CCD vs DoseCCD vs HV before and after (500µm thickness) Irradiated one individual pad of each prototype to about 1 – 1.5 MGy. Starting at about 50% of the sensor thickness. ~ 80% decrease Ending at about 3 %

12. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 12 GaAs after Irradiation Partially irradiated pads show two very distinct signal peaks. High: signal from not irradiated area Low: signal after ~1.5 MGy Leakage currents increase by about a factor of 2...but this time it is in the μA range.

13. 11/1/2007C.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

14. 11/1/2007C.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/

15. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 15 Backup Slides

16. 11/1/2007C.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 X 0 o3.5mm W and 0.3mm sensor  Angular coverage from 5mrad to 28 mrad  Moliére radius R M ≈ 1cm  Segmentation between 0.5 and 0.8 x R M BeamCal LDC ~20 cm ~ 25 cm

17. 11/1/2007C.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- e+e+ Creation of beamstrahlung at the ILC ≈ 5 MGy/a e-e- e-e- γ e-e- γ e+e+ e.g. Breit-Wheeler process V.Drugakov 6X 0 Energy deposition and spectrum of shower particles.

18. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 18 Procedure Correction factors are obtained from a GEANT4 simulation of the geometry  R = N FC /N Sensor ~ 0.96  /particle = 5.63 MeV/cm Apply HV to the DUT Measure CCD ~20 min Irradiate the sample ~1 hour During the irradiation the Faraday cup current is monitored and used to calculate the accumulated dose with a total error of ΔD/D < 10%

19. 11/1/2007C.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

20. 11/1/2007C.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

21. 11/1/2007C.Grah: Radiation Hard Sensors for BeamCal 21 Polarization of Single-crystalline CVD Diamond Observation a) Signal current and from MIPs decreases.  No trapping-detrapping on short timescales Observation b) MIP response is dependent on time (after setting HV) and rate Homogeneous creation of traps + creation of eh pairs by a MIP plus electric field leads to polarization. Measurement at 100V Prediction at 100V Prediction at 200V Prediction at 200V (switching HV) Measurement at 200V (switching HV) Dose calculation uncorrected! Dose calculation uncorrected!