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Plans for Radiation Damage Studies for Si Diode Sensors Subject to 1 GRaD Doses. SLAC Testbeam Workshop March 17 2011. The Issue: ILC BeamCal Radiation Exposure. ILC BeamCal: Covers between 5 and 40 miliradians Radiation doses up to 100 MRad per year

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

SLAC Testbeam Workshop

March 17 2011


The Issue: ILC BeamCal Radiation Exposure Subject to 1 GRaD Doses

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


Hadronic Processes in EM Showers Subject to 1 GRaD Doses

  • 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


Proposal: JLAB Hall B Beam Dump (Plan to run 0.05 Subject to 1 GRaD Doses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?


Proposed split radiator configuration Subject to 1 GRaD Doses

5mm Tungsten “pre”

13mm Tungsten “post”

Separated by 1m

Fluence (particles per cm2)

1.0

2.0

3.0

5

Radius (cm)


  • Rastering Subject to 1 GRaD Doses

  • 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


  • ISSUES/CONCERNS/FEATURES Subject to 1 GRaD Doses

  • 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


  • ISSUES/CONCERNS/FEATURES II Subject to 1 GRaD Doses

  • 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.


Parameters required for beam tests
Parameters required for Beam Tests Subject to 1 GRaD Doses

To the presenter at the ESTB 2011 Workshop: please, fill in the table (at best) with the important parameters needed for your tests


  • SUMMARY Subject to 1 GRaD Doses

  • 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)


Backup Subject to 1 GRaD Doses


Shower Max Results Subject to 1 GRaD Doses

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!


G.P. Summers et al., IEEE Trans Nucl Sci Subject to 1 GRaD Doses40, 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


5.5 GeV Shower Profile Subject to 1 GRaD Doses

“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)


Fluence (e Subject to 1 GRaD Doses- 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)


5.5 GeV Electrons After 18mm Tungsten Block Subject to 1 GRaD Doses

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)


NIEL (Non-Ionizing Energy Loss) Subject to 1 GRaD Doses

  • 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


BeamCal Incident Energy Distribution Subject to 1 GRaD Doses

2

4

6

8

10

e+/e- ENERGY (GEV)

18


Wrap-up Subject to 1 GRaD Doses

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


Rates (Current) and Energy Subject to 1 GRaD Doses

  • 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


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