1. Plans for Radiation Damage Studies for Si Diode Sensors Subject to 1 GRaD Doses SLAC Testbeam Workshop August 23 2012

2. 2 The Issue: ILC BeamCal Radiation Exposure ILC BeamCal: Covers between 5 and 40 miliradians Radiation doses up to 100 MRad per year Radiation initiated by electromagnetic particles (most extant studies for hadron – induced) EM particles do little damage; might damage be come from small hadronic component of shower?

3. 3 Hadronic Processes in EM Showers There seem to be three main processes for generating hadrons in EM showers (all induced by photons): Nuclear (“giant dipole”) resonances Resonance at 10-20 MeV (~E critical ) Photoproduction Threshold seems to be about 200 MeV Nuclear Compton scattering Threshold at about 10 MeV;  resonance at 340 MeV  These are largely isotropic; must have most of hadronic component develop near sample

4. Proposal: JLAB Hall B Beam Dump (Plan to run 0.05  A through next May)  Total power in beam ~250W. Oops – too much background for Hall B! What about SLAC? Pre-radiator Post-radiator and sample

5. 5 Hadronic Processes in EM Showers Status: Thermal prototype under testing at SCIPP

6. 6 Proposed split radiator configuration Radius (cm) Fluence (particles per cm 2 ) 5mm Tungsten “pre” 13mm Tungsten “post” Separated by 1m 1.02.03.0

7. Rastering Need uniform illumination over 0.25x0.75 cm region (active area of SCIPP’s charge collection measurement apparatus).  Raster in 0.05cm steps over 0.6x1.5 cm, assuming fluence profile on prior slide (see next slide for result) Exposure rate: e.g. 100 MRad at 1 nA 13.6 GeV e -  ~ 6 Hr

8. ISSUES/CONCERNS/FEATURES Alignment and Rastoring We’ll need to know the absolute beam location to 1mm or so Will rastoring be available, or will we need to move samples around ourselves? It would be much easier for our design if the beam moved. Radiomtery We’ll need dosimetry at ~10% accuracy Will we need to worry about activation (we plan to do our damage assessment back in Santa Cruz

9. ISSUES/CONCERNS/FEATURES II Long Running periods (~1 shift for 100 MRad; many samples) Can we run parasitically? What access can we have during parasitic running? Infrastructure Temperature control (thermal load from full beam ~500W, plus need to avoid annealing), Control systems, etc.

10. Parameters required for Beam Tests Beam parametersValueComments Particle Typee- Positrons would be fine Energy (2-13 GeV)Maximum Rep Rate (1-5 Hz nominal, Bursts up to 120 Hz) MaximumAs long as we can figure out how to handle 500W Charge per pulse or number of electrons/pulse Maximum Energy SpreadNot a concern Bunch length r.m.s.Not a concern Beam spot size, x-y, emittanceLess than ~1mmRastering would be very helpful! Others (cooling water, gasses, etc.)Rastering, cooling (W or Pb?)Tungsten for target? (Otherwise Pb) LogisticsRequirements Space requirements (H x W x L)  m x 1m x 1m (plus 20cm x 20cm x 20cm 1-2 m upstream) Others (cooling water, gasses, electricity, etc.)Need to figure out how to cool 500W Duration of Test and Shift UtilizationAbout 1 week; perhaps no owl? Whatever we could get really. Desired Calendar DatesWinter 2013 To the presenter at the ESTB 2012 Workshop: please, fill in/update the table (at best) with the important parameters needed for your tests

11. SUMMARY ILC BeamCal demands materials hardened for unprecedented levels of electromagnetic-induced radiation 10-year doses will approach 1 GRad. Not clear if hadrons in EM shower will play significant role  need to explore this At 1 nA, 1 GRad takes a long time (60 hours); multiply time ~10 samples  really long time More beam current (?) Start with 100 MRad studies (already interesting)

12. Backup

13. Parameters required for Beam Tests Beam parametersValueComments Particle Typeelectron EnergyMaximum Rep RateMaximum Charge per pulseMaximum Energy SpreadNot a concern Bunch length rmsNot a concern Beam spot size, x-yLarge is helpfulUp to ~1 cm rms Others (emittance, …)Not a concern LogisticsRequirements Space requirements (H x W x L)  m x 1m x 1m (plus 20cm x 20cm x 20cm 1-2 meters upstream) Duration of Test and Shift UtilizationDepends on available current Desired Calendar DatesCY 2012 (flexible) To the presenter at the ESTB 2011 Workshop: please, fill in the table (at best) with the important parameters needed for your tests

14. 14 Shower Max Results  Photon production ~independent of incident energy! 1.02.03.0 Electrons, per GeV incident energy Photons per electron Photons with E > 10 MeV per electron, x10 Photons with E > 100 MeV per electron, x 100

15. 15 Damage coefficients less for p-type for E e- < ~1GeV (two groups); note critical energy in W is ~10 MeV But: Are electrons the entire picture? NIELe - Energy 2x10 -2 0.5 MeV 5x10 -2 2 MeV 1x10 -1 10 MeV 2x10 -1 200 MeV G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)

16. 16 5.5 GeV Shower Profile Radius (cm) Fluence (particles per cm 2 ) e + e - (x10) All  E  > 10 MeV (x2) E  > 100 MeV (x20) Remember: nuclear component is from photons in 10-500 MeV range. “Pre”“Post”

17. mm from center 01234 013.012.811.89.98.2 113.312.912.0 213.312.912.0 313.112.811.88.2 413.012.611.7 512.3 611.610.7 710.4 88.68.06.4 Fluence (e - and e + per cm 2 ) per incident 5.5 GeV electron (5cm pre-radiator 13 cm post-radiator with 1m separation) ¼ of area to be measured Center of irradiated area ¼ of rastoring area (0.5mm steps)

18. 18 5.5 GeV Electrons After 18mm Tungsten Block Radius (cm) Fluence (particles per cm 2 ) Boundary of 1cm detector Not amenable for uniform illumination of detector. Instead: split 18mm W between “pre” and “post” radiator separated by large distance Caution: nuclear production is ~isotropic  must happen dominantly in “post” radiator!

19. 19 NIEL (Non-Ionizing Energy Loss) Conventional wisdom: Damage proportional to Non- Ionizing Energy Loss (NIEL) of traversing particle NIEL can be calculated (e.g. G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 [1993]) At E c Tungsten ~ 10 MeV, NIEL is 80 times worse for protons than electrons and NIEL scaling may break down (even less damage from electrons/positrons) NIEL rises quickly with decreasing (proton) energy, and fragments would likely be low energy  Might small hadronic fractions dominate damage?

20. 20 e +/ e - ENERGY (GEV) BeamCal Incident Energy Distribution 246810

21. 21 Wrap-up Worth exploring Si sensors (n-type, Czochralski?) Need to be conscious of possible hadronic content of EM showers Energy of e - beam not critical, but intensity is; for one week run require E beam (GeV) x I beam (nA) > 50 SLAC: Summer-fall 2011 ESA test beam with E beam (GeV) x I beam (nA)  17 – is it feasible to wait for this?

22. 22 Rates (Current) and Energy Basic Idea: Direct electron beam of moderate energy on Tungsten radiator; insert silicon sensor at shower max For Si, 1 GRad is about 3 x 10 16 /cm 2, or about 5 mili-Coulomb/cm 2  Reasonably intense moderate-energy electron or photon beam necessary What energy…?