Polycrystalline CVD Diamonds for the Beam Calorimeter of the ILC C. Grah 1, U. Harder 1, H. Henschel 1, E. Kouznetsova 1, W. Lange 1, W. Lohmann 1, M. Ohlerich 1,3, R. Schmidt 1,3, K. Afanaciev 2, A. Ignatenko 2 N18-6, Tuesday, Oct. 31 st 1 Linear Collider, DESY, Zeuthen, Germany 2 NCPHEP BSU, Minsk, Belarus 3 BTU Cottbus, Germany

10/31/2006 C.Grah: CVD Diamonds2 Contents  Very forward region of the detectors for the International Linear Collider  BeamCal – requirements  Testbeam at CERN  Linearity of the response of CVD diamonds  Testbeam at the TU Darmstadt  Radiation hardness of CVD diamonds  Conclusions

10/31/2006 C.Grah: CVD Diamonds3 Very Forward Region of the ILC Detectors Interaction point  The purpose of the instrumentation of the very forward region is:  Hermeticity: increase the coverage to polar angles > 5mrad  Optimize Luminosity  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

10/31/2006 C.Grah: CVD Diamonds4 The Challenges for BeamCal  e+e- pairs from beamstrahlung are deflected into the BeamCal  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- e+e+ Creation of beamstrahlung at the ILC ≈ 1 MGy/a ≈ 5 MGy/a e-e- e-e- γ e-e- γ e+e+ e.g. Breit-Wheeler process

10/31/2006 C.Grah: CVD Diamonds5 Polycrystalline Chemical Vapour Deposited Diamonds  pCVD diamonds are an interesting material:  radiation hardness (e.g. LHC pixel detectors)  advantageous properties like: high mobility, low ε R = 5.7, thermal conductivity  availability on wafer scale  Samples from two manufacturers are under investigation:  Element Six TM  Fraunhofer Institute for Applied Solid-State Physics – IAF  1 x 1 cm 2  μm thick (typical thickness 300μm)  Ti(/Pt)/Au metallization (courtesy of IAF)

10/31/2006 C.Grah: CVD Diamonds6 Linearity Test at CERN PS Hadronic beam, 3 & 5 GeV Fast extraction mode ~ particles / ~10 ns ADC signal gate 10 ns 17 s Diamond Setup Beam Scint.+ PMTs. Response of diamond sensor to beam particles (no preamplifier/attenuated) Photomultiplier signals

10/31/2006 C.Grah: CVD Diamonds7 Response vs. Particle Fluence 30% deviation from a linear response for a particle fluence up to ~10 6 MIP/cm 2 The deviation is at the level of the systematic error of the fluence calibration. E64 FAP2 Fraunhofer IAF Element Six

10/31/2006 C.Grah: CVD Diamonds8 High Dose Irradiation  Irradiation up to several MGy using the injector line of the S-DALINAC: 10 ± MeV and beam currents from 10 to 100 nA corresponding to about 59 to 590 kGy/h Superconducting DArmstadt LINear ACcelerator Technical University of Darmstadt Energy spectrum of shower particles in BeamCal V.Drugakov 2X 0

10/31/2006 C.Grah: CVD Diamonds9 Preparations and Programme GEANT4 simulation of the geometry => R = N FC /N Sensor = 0.98 /particle = 5.63 MeV/cm Beam setup SampleThickness, 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

10/31/2006 C.Grah: CVD Diamonds10 Realization: Beam Setup exit window of beam line collimator (I Coll ) sensor box (I Dia, T Dia, HV) Faraday cup (I FC, T FC )

10/31/2006 C.Grah: CVD Diamonds11 CCD Setup typical spectrum of an E6 sensor Sr90 source Preamplifier Sensor box Trigger box & Gate PA discr delay ADC Sr 90 diamond Scint. PM1 PM2 Setups partly financed by EUDET.

10/31/2006 C.Grah: CVD Diamonds12 Results: CCD vs. Dose 100 nA (E6_4p)100 nA (FAP5) Silicon starts to degrade at 30 kGy. High leakage currents. Not recoverable. CCD = Q meas /Q induced x thickness Bias voltage = 400V ≈> 1 V/μm After absorbing 7MGy: CVD diamonds still operational.

10/31/2006 C.Grah: CVD Diamonds13 Behaviour after Irradiation Slight increase of currents for higher doses. No significant change of the current-voltage characteristics up to 1.5 MGy.

10/31/2006 C.Grah: CVD Diamonds14 CCD Behaviour after Irradiation after 1.5 MGy ~ -30% ~ -80% after 7 MGy

10/31/2006 C.Grah: CVD Diamonds15 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

10/31/2006 C.Grah: CVD Diamonds16 Summary  BeamCal is an important part of the instrumentation of the very forward region of the ILC detectors.  The requirements on the radiation hardness and linearity of the sensors are challenging.  PCVD diamonds are an interesting material for this task.  The linearity of pCVD diamonds up to particle fluences of 10 6 particles/cm 2 /10ns is better than 30%.  High dose irradiation using 10MeV electrons shows:  all CVD diamonds stay functional even after absorbing up to 7MGy.  degradation of the signal at high doses and dose rates.  partial recovery of the signal after absorbing additional small doses (~20 Gy).  wide variation of the signal sizes as a function of the absorbed dose is an issue for the use as a sensor for BeamCal.