1. Radiation Hard Sensors for the BeamCal of the ILC C. Grah FCAL Collaboration 10 th ICATPP Conference, Villa Olmo

2. 10.10.2007 C.Grah: Radhard Sensors for BeamCal2 Contents  The ILC and the very forward region of the detectors for the International Linear Collider  BeamCal – requirements  Radiation hard materials under investigation:  CVD diamond  Silicon  GaAs and SiC  Conclusions

3. 10.10.2007 C.Grah: Radhard Sensors for BeamCal3 The International Linear Collider ILC Parameters of the ILC: e + e - accelerator, sc cavities, gradient 31.5 MV/m => 30km long CMS energy: 200 to 500 GeV (possible upgrade to 1 TeV) One interaction region, beam crossing angle of 14mrad and two detectors („push-pull“ scenario) Peak luminosity: 2 x 10 34 cm -2 s -1 typical beam size: (h x v) 650 nm x 5.7nm & beam intensity 2 x 10 10 e + e - ~ 30 km

4. 10.10.2007 C.Grah: Radhard Sensors for BeamCal4 Very Forward Region of the ILC Detectors  R&D of the detectors in the forward region is done by the FCAL Collaboration.  Precise (LumiCal) and fast (BeamCal) luminosity measurement  Hermeticity (electron detection at low polar angles)  Mask for the inner detectors  Not shown here: GamCal, a beamstrahlung photon detector at about 180m post-IP. LumiCal TPC ECAL HCAL BeamCal

5. 10.10.2007 C.Grah: Radhard Sensors for BeamCal5 The Beam Calorimeter - BeamCal Interaction point  Compact EM calorimeter with sandwich structure:  30 layers of 1 X 0 o3.5mm W absorber and 0.3mm radiation hard sensor  Angular coverage from 5mrad to 28 mrad (6.0 > |η| > 4.3)  Moliére radius R M ≈ 1cm  Segmentation between 0.5 and 0.8 x R M BeamCal LDC ~10cm ~12cm Space for electronics

6. 10.10.2007 C.Grah: Radhard Sensors for BeamCal6 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.  ~ 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

7. 10.10.2007 C.Grah: Radhard Sensors for BeamCal7 Diamond as Sensor Material  Manufacturing of diamond has become more and more available. CVD deposition of polycrystalline diamonds is available at wafer scale (3”-6” diameter) Properties:DiamondSilicon Hardness* 10,000 kg/mm 2 1100 kg/mm 2 Density 3.52 g/cm 3 2.33 g/cm 3 Atom density* 1.77 x 10 23 1/cm 3 0.50 x 10 23 1/cm 3 Thermal expansion coefficient 1.1 ppm/K2.6 ppm/K Thermal conductivity* 20.0 W/cmK1.412 W/cmK Dielectric strength 10 MV/cm0.3 MV/cm Resistivity 10 13 - 10 16 Ωcm2.3 x 10 5 Ωcm Electron mobility 2,200 cm 2 /Vs1350 cm 2 /Vs Hole mobility 1,600 cm 2 /Vs480 cm 2 /Vs Bandgap 5.45 eV1.12 eV Energy/eh-pair13eV3.62 eV Av. eh/100μm (MIP)36007800 *highest value of all solid materials (diamond values from Fraunhofer IAF webpage)

8. 10.10.2007 C.Grah: Radhard Sensors for BeamCal8 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  200-900 μm thick (typical thickness 300μm)  Ti(/Pt)/Au metallization (courtesy of IAF)

9. 10.10.2007 C.Grah: Radhard Sensors for BeamCal9 IV Characteristics  Typical current-voltage characteristics of a good pCVD diamond.  No breakthrough up to 500V.  Very low currents of a few picoamperes.  Symmetric (linear) behavior (ramping up)  Hysteresis observed for all pCVD samples (ramping down).

10. 10.10.2007 C.Grah: Radhard Sensors for BeamCal10 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

11. 10.10.2007 C.Grah: Radhard Sensors for BeamCal11 CCD Measurement ~ CCD CCD = Charge Collection Distance = mean drift distance of the charge carriers = charge collection efficiency x thickness ADC Channels ~ charge Counts

12. 10.10.2007 C.Grah: Radhard Sensors for BeamCal12 CCD Behavior  CCD is a function of the applied electric field.  Saturation at about 1V/µm.

13. 10.10.2007 C.Grah: Radhard Sensors for BeamCal13 Linearity Test at CERN PS Hadronic beam, 3 & 5 GeV Fast extraction mode ~10 4 -10 7 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

14. 10.10.2007 C.Grah: Radhard Sensors for BeamCal14 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

15. 10.10.2007 C.Grah: Radhard Sensors for BeamCal15 High Dose Irradiation  Irradiation up to several MGy using the injector line of the S-DALINAC: 10 ± 0.015 MeV and beam currents from 10 to 100 nA corresponding to about 60 to 600 kGy/h Superconducting DArmstadt LINear ACcelerator Technical University of Darmstadt Energy spectrum of shower particles in BeamCal V.Drugakov 6X 0

16. 10.10.2007 C.Grah: Radhard Sensors for BeamCal16 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

17. 10.10.2007 C.Grah: Radhard Sensors for BeamCal17 Testbeam Setup BeamCollimatorSensorFaraday Cup

18. 10.10.2007 C.Grah: Radhard Sensors for BeamCal18 Results: CCD vs. Dose 100 nA (E6_4p)100 nA (FAP5) Silicon starts to degrade at 30 kGy. High leakage currents. Not recoverable. After absorbing 7MGy: CVD diamonds still operational.

19. 10.10.2007 C.Grah: Radhard Sensors for BeamCal19 Behaviour after Irradiation Slight increase of currents for higher doses. No significant change of the current-voltage characteristics up to 1.5 MGy.

20. 10.10.2007 C.Grah: Radhard Sensors for BeamCal20 CCD Behaviour after Irradiation after 1.5 MGy ~ -30% ~ -80% after 7 MGy

21. 10.10.2007 C.Grah: Radhard Sensors for BeamCal21 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

22. 10.10.2007 C.Grah: Radhard Sensors for BeamCal22 Monocrystalline CVD Diamond Sensors sCVD diamond area: a few mm 2, ~thickness 300 µm, metallization Ø3mm -25 V IV Characteristics (too low current for our setup) 100% efficient at low electric fields!

23. 10.10.2007 C.Grah: Radhard Sensors for BeamCal23 GaAs Sensor Material  Produced by the Siberian Institute of Technology, Tomsk  semi-insulating GaAs doped by Sn (shallow donor)  compensated by Cr (deep acceptor): to compensate electron trapping centers EL2+ and provide i-type conductivity.

24. 10.10.2007 C.Grah: Radhard Sensors for BeamCal24 GaAs Prototype Details  500 µm thick detector, divided into 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 and structure is provided by metallization (similar to diamond)

25. 10.10.2007 C.Grah: Radhard Sensors for BeamCal25 Properties of the GaAs Sensor Rpad  500 MOhm, pad capacity about 12 pF, dark current 1 μA @ 500 V CCD = 50% of sensor thickness

26. 10.10.2007 C.Grah: Radhard Sensors for BeamCal26 First View on Testbeam Results  Spatial CCD distribution corresponds to the beam profile  Pad with 2 CCD regions - due to collimation while irradiation → No trap diffusion  Dark current increased up to about 2 μA @ 500 V beam spot (~1 MGy)

27. 10.10.2007 C.Grah: Radhard Sensors for BeamCal27 Radiation Hard Silicon 400 V reverse voltage depletion zone mCz Si, radiation hard, thickness 380 μm, 5x5 mm 2 n+ on n-configuration works as solid state ionization chamber, but active volume = depletion zone signal by drifting excess charge carriers guard rings to avoid surface currents guard rings

28. 10.10.2007 C.Grah: Radhard Sensors for BeamCal28 Radhard Silicon - Before Irradiation depletion voltage: 336 V → operational voltage 400 V

29. 10.10.2007 C.Grah: Radhard Sensors for BeamCal29 Silicon - Under Irradiation Signal/Noise vs DOSE Intended as a first step using the radhard silicon CCD remained constant Noise increased strongly No cooling CCD vs DOSE

30. 10.10.2007 C.Grah: Radhard Sensors for BeamCal30 Silicon Carbide  SiC is a potential sensor material with a high bandgap of > 3eV  First SiC material provided by the Technical University of Cottbus (BTU)  ~1cm 2 size  very asymmetric behavior with high dark currents at low voltages => no signal detectable.  Need material with higher resistivity.

31. 10.10.2007 C.Grah: Radhard Sensors for BeamCal31 Summary  The FCAL Collaboration develops the detectors in the very forward region of the ILC detectors.  BeamCal is an important part of the instrumentation.  The requirements on the radiation hardness and linearity of the sensors are challenging.  CVD diamonds, radiation hard silicon, GaAs and SiC are interesting materials for this task and are under investigation. http://www-zeuthen.desy.de/ILC/fcal/

32. Cooperation with: SLAC Stanford University Iowa State University Wayne State University FCAL Collaboration Aim: design and construction of Collaboration High precision design luminosity detectors beam monitors photon detectors University of Colorado Brookhaven National Lab NY Yale University New Haven Laboratoire de l Accélérateur Linéaire Orsay Royal Holloway University London AGH University, Cracow I nstitute of N uclear P hysics, Cracow DESY J oint I nstitute N uclear R esearch Dubna N ational C enter of P article & HEP Minsk Prague Acad. of Science VINCA Inst. f. Nuclear Science Belgrade Tel Aviv University http:// www-zeuthen.desy.de/ILC/fcal / EUROTeV, EUDET, NoRHDIA INTAS