Plans for Radiation Damage Studies for Si Diode Sensors Subject to 1 GRaD Doses

1. Plans for Radiation Damage Studies for Si Diode Sensors Subject to 1 GRaD Doses SLAC Testbeam Workshop March 17 2011

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? 2

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 (~Ecritical) • 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 3

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

5. Proposed split radiator configuration 5mm Tungsten “pre” 13mm Tungsten “post” Separated by 1m Fluence (particles per cm2) 1.0 2.0 3.0 5 Radius (cm)

6. Rastering • Need uniform illumination over 0.25x0.75 cmregion (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. 1 GRad at 1 nA 13.6 GeV e-  ~ 60 Hours

7. 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

8. ISSUES/CONCERNS/FEATURES II • Long Running periods (~60 hours for 1 GRad) • Can we run parasitically? • What access can we have during parasitic running? • Infrastructure • Temperature control (thermal load from beam ~10W, plus need to avoid annealing), • Control systems, etc.

9. Parameters required for Beam Tests To the presenter at the ESTB 2011 Workshop: please, fill in the table (at best) with the important parameters needed for your tests

10. 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)

11. Backup

12. Shower Max Results Photons with E > 100 MeV per electron, x 100 Photons with E > 10 MeV per electron, x10 Photons per electron Electrons, per GeV incident energy 1.0 2.0 3.0 12  Photon production ~independent of incident energy!

13. G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993) NIELe- Energy 2x10-2 0.5 MeV 5x10-2 2 MeV 1x10-1 10 MeV 2x10-1 200 MeV Damage coefficients less for p-type for Ee- < ~1GeV (two groups); note critical energy in W is ~10 MeV But: Are electrons the entire picture? 13

14. 5.5 GeV Shower Profile “Pre” “Post” e+e- (x10) All  Remember: nuclear component is from photons in 10-500 MeV range. Fluence (particles per cm2) E > 100 MeV (x20) E > 10 MeV (x2) 14 Radius (cm)

15. Fluence (e- and e+ per cm2) per incident 5.5 GeV electron (5cm pre-radiator 13 cm post-radiator with 1m separation) Center of irradiated area ¼ of area to be measured ¼ of rastoring area (0.5mm steps)

16. 5.5 GeV Electrons After 18mm Tungsten Block 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! Boundary of 1cm detector Fluence (particles per cm2) 16 Radius (cm)

17. 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 EcTungsten ~ 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? 17

18. BeamCal Incident Energy Distribution 2 4 6 8 10 e+/e- ENERGY (GEV) 18

19. 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 Ebeam(GeV) x Ibeam(nA) > 50 SLAC: Summer-fall 2011 ESA test beam with Ebeam(GeV) x Ibeam(nA) 17 – is it feasible to wait for this? 19

20. 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 1016/cm2, or about 5 mili-Coulomb/cm2 • Reasonably intense moderate-energy electron or photon beam necessary What energy…? 20