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

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

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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 DosesA 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 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

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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