14 December nd CARAT Workshop, GSI, Darmstadt1 Radiation hardness studies with relativistic electrons Sergej Schuwalow, Uni-HH / DESY On behalf of FCAL collaboration

14 December nd CARAT Workshop, GSI, Darmstadt2 Content Why electrons? scCVD diamond irradiation at TU-Darmstadt CCD vs dose Polarization effects Beam pumping tests Measurements at ELBE - Rossendorf Summary

14 December nd CARAT Workshop, GSI, Darmstadt3 ILC – International Linear Collider First stage : 90 – 500 GeV Second stage : up to 1 TeV Luminosity : 500 fb -1 / 4years 1 ab -1 at 1 TeV L ~ 2 x cm -2 s -1 Polarisation : 80% e- 50% e+ (later phase) Beam energy : < uncertainty Options : GigaZ (high lumi running at the Z), e- ,  - 

14 December nd CARAT Workshop, GSI, Darmstadt4 Two photon process cross section cross section about 10 5 larger than SUSY cross section. Serious source of background for SUSY if not tagged. Beam Calorimeter Studies e+e+ e- e-   q.l q,l in the detector very forward into BeamCal very forward into BeamCal From U.Nauenberg

14 December nd CARAT Workshop, GSI, Darmstadt5 Beam related background e+e+ e-e-   into beampipe

14 December nd CARAT Workshop, GSI, Darmstadt6 Beam related background e+e+ e-e-   e+e- pairs B in the detector

14 December nd CARAT Workshop, GSI, Darmstadt7 Beam related background e+e+ e-e-   e+e- pairs B Detector solenoid field BeamCal ~15000 e + e - pairs per BX TeV total energy deposition Up to 10 MGy annual dose at showermax depth ~10 MeV electrons Radiation hard sensors 2  - event

14 December nd CARAT Workshop, GSI, Darmstadt8 Very Forward Region of the ILD Detector BeamCal, Pair Monitor LumiCal LHCal

14 December nd CARAT Workshop, GSI, Darmstadt9 CLIC Forward Region LumiCal BeamCal

14 December nd CARAT Workshop, GSI, Darmstadt10 High dose irradiation at the beam Beam Collimator DetectorDetector Detector box Faraday cup

14 December nd CARAT Workshop, GSI, Darmstadt11 Irradiation of scCVD Diamond After 5 MGy dose diamond detector is operational CCD is decreasing with the absorbed dose Generation of trapping centers due to irradiation Traps release? CCD current < CCD MIP ? Too high ‘missing charge’ ~N atoms in the sample Pure trapping mechanism is contradictory Recombination is important Polarization? ‘missing charge’ DALINAC, TU-Darmstadt June 2007 CCD from 90 Sr setup CCD from I sens

14 December nd CARAT Workshop, GSI, Darmstadt12 Irradiation of scCVD Diamond No annealing! 1.5 years, a lot of tests with 90 Sr source, UV-light, several TSC measurements After 10 MGy absorbed dose MIP signal is still detectable Leakage current is very small (few ~pA) Continued in December 2008 Jun 2007 Data Dec 2008 Data 10 MGy – 3.65·10 16 e/cm 2

14 December nd CARAT Workshop, GSI, Darmstadt13 MIP Response of scCVD Diamond Diamond 90 Sr Scint. PM1 PM2 discr PAdelay & ADC 90 Sr Source Sensor box & Preamplifier Trigger box ADC spectrum 90 Sr spectrum Number of electrons Energy of electrons [MeV] I(V) measurements MIPs

14 December nd CARAT Workshop, GSI, Darmstadt14 Damaged Sensor under 90 Sr source: CCD vs time Illuminate by UV-light to free all traps Apply HV and source 90 Sr -HV

14 December nd CARAT Workshop, GSI, Darmstadt15 Damaged Sensor under 90 Sr source: CCD vs time 90 Sr ±HV Illuminate by UV-light to free all traps Apply HV and source

14 December nd CARAT Workshop, GSI, Darmstadt16 Damaged Sensor under 90 Sr source: CCD vs time 90 Sr ±HV Illuminate by UV-light to free all traps Apply HV and source

14 December nd CARAT Workshop, GSI, Darmstadt17 Damaged Sensor under 90 Sr source: CCD vs time 90 Sr ±HV Illuminate by UV-light to free all traps Apply HV and source Short living traps

14 December nd CARAT Workshop, GSI, Darmstadt18 Long-term signal evolution in radiation damaged sCVDD sensor Try to minimize an influence of the measurement onto the filled trap distribution Use the source only for short CCD evaluation runs Polarization is seen even after 1 month after the initial pumping – long living traps, possibility to fill all of them! t 0 = 35 days

14 December nd CARAT Workshop, GSI, Darmstadt19 Beam Pumping Test Trigger BoxLinear Drive 90 Sr Source Collimator Faraday Cup Detector+Preamp Box Collimator Beam Use intensive beam to fill up short living traps Move (remotely) detector/preamp box to the low intensity 90 Sr line Measure signal evolution with time since beam-off

14 December nd CARAT Workshop, GSI, Darmstadt20 Beam Pumping Test Clear indication to the presence of fast decaying traps. Additional polarization due to shallow traps filling Faster trap release at higher bias voltage: “Poole-Frenkel”-like effect? 5 MGy 10 MGy Dose rate ~ 100 x highest dose ILC detector

14 December nd CARAT Workshop, GSI, Darmstadt21 TSC measurements At least 3 levels are visible: trap1trap2trap3 Ec-E T [eV] n T 0 [10 14 cm - 3 ] After 5 MGy Trap concentration ~ cm -3 (still 8 orders of magnitude less than normal atom density)

14 December nd CARAT Workshop, GSI, Darmstadt22 CCD 0 vs Dose – free traps case Are thin sensors more radiation hard? Plan: irradiate thin (~100 μm) sensor at the test beam in Feb 2010

14 December nd CARAT Workshop, GSI, Darmstadt23 Testbeam February 2010, Dresden 20 MeV electron beam ELBE facility (FZD Rossendorf)

14 December nd CARAT Workshop, GSI, Darmstadt24 Faraday cup Collimator Sensor box Bias voltage source FC and Collimator current read-out Oscilloscope Testbeam February 2010, Dresden

14 December nd CARAT Workshop, GSI, Darmstadt25 Free trap charge collection efficiency of radiation damaged scCVD diamond When free traps are uniformly distributed in the bulk, CCE could be calculated analytically: Where D – detector thickness, a is proportional to the trap density and trapping cross section. Free trap case => sensor is irradiated by UV light before CCE measurement. E = 6000 V/cm Compatible with TSC measurements

14 December nd CARAT Workshop, GSI, Darmstadt26 Summary The performance of scCVD Diamond sensors were studied at MeV electron beam as a function of absorbed dose up to 10 MGy Strong polarization effects are observed in the radiation damaged scCVD Diamond detector Polarization significantly decreases the detector charge collection efficiency in addition to pure trapping mechanism Method of switching bias HV polarity allows to suppress bulk polarization caused by long-living traps Beam pumping tests indicate that short-living traps are responsible for the residual detector inefficiency Additional studies of radiation damaged sensor CCD vs temperature are planned

14 December nd CARAT Workshop, GSI, Darmstadt27 Thank you

14 December nd CARAT Workshop, GSI, Darmstadt28 Diamond properties Density 3.52 g cm -3 Dielectric constant 5.7 Breakdown field 10 7 V cm -1 Resistivity >10 11 Ω cm Band gap 5.5 eV Electron mobility 1800 (4500) cm 2 V -1 s -1 Hole mobility 1200 (3800) cm 2 V -1 s -1 Energy to create e-h pair 13.1 eV Average signal created 36 e μm -1 *High purity single crystal CVD diamond

14 December nd CARAT Workshop, GSI, Darmstadt29 BeamCal Sensors example Baseline: GaAs kGy Up to 600 kGy a MIP signal from all sensors is clearly seen Sensors with a lower concentration of shallow donor and Cr as deep acceptor show better radiation tolerance (up to 1MGy) GaAs BeamCal sector prototype

14 December nd CARAT Workshop, GSI, Darmstadt30 BeamCal Sensors, Sapphire Band gap: 9.9 eV (diamond: 5.5 eV, Si: 1.12 eV) Single crystal, 1x1x0.05 cm 3 Wafer: up to 30 cm diameter Metallization: Al 200 nm or 50/50/100 nm Al/Ti/Au Normalized ratio of the detector and Faraday cup currents Charge collection efficiency: few % for nonirradiated samples ~ 30 % of the initial charge collection efficiency after 12 MGy

14 December nd CARAT Workshop, GSI, Darmstadt31 Study of Sapphire sensors (preliminary)