Electromagnetic Radiation Hardness for the ILC BeamCal Sensors
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Electromagnetic Radiation Hardness for the ILC BeamCal Sensors. Argonne SiD Workshop Friday, June 4 2010 Bruce Schumm Santa Cruz Institute for Particle Physics. The SCIPP/UCSC ILC R&D GROUP. Faculty/Senior Vitaliy Fadeyev Bruce Schumm. Collaborators Takashi Maruyama Tom Markiewicz

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Electromagnetic Radiation Hardness for the ILC BeamCal Sensors

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Electromagnetic Radiation Hardness for the ILC BeamCal Sensors

Argonne SiD Workshop

Friday, June 4 2010

Bruce Schumm

Santa Cruz Institute for Particle Physics



Vitaliy Fadeyev

Bruce Schumm


Takashi Maruyama

Tom Markiewicz



Spencer Key

Donish Khan

Some notes:

  • Beam Calorimeter is a sizable project, ~2 m2 of sensors.

  • Sensors are in unusual regime: ~ 1 GRad of e+/e-; 1014 n/cm2 after several years.

  • There are on-going studies with GaAs, Diamond, Sapphire materials (FCAL report, Nov 2009).

  • We’ll concentrate on mainstream Si technology proven by decades of technical development.

  • There is some evidence that p-type Si may be particularly resilient…


Rates (Current) and Energy

  • Basic Idea:

  • Direct electron beam of moderate energy on Tungsten radiator; follow with silicon sensor at shower max

  • For Si, 1 GRad is about 3 x 1016/cm2, or about 5 mili-Coulomb

  • Current scale is A, which points to the 1-5 GeV beam at CBAF (Jefferson Lab, Virginia, USA)


G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)

NIELe- Energy

2x10-20.5 MeV

5x10-22 MeV

1x10-110 MeV

2x10-1200 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?


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

  •  Flux through silicon sensor should be ~10 MeV e/, but also must appropriately represent hadronic component


1mm Downstream of 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


Fluence (particles per cm2)


Radius (cm)

5.5 GeV Shower Profile



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)


Radius (cm)

Possible split radiator configuration

(needs more study)

Boundary of 1cm


6mm Tungsten “pre”

12mm Tungsten “post”

Separated by 2m

Fluence (particles per cm2)


Radius (cm)

No Beam Spread

Beam Spread = 1mm

Radial Fluence Distributions for Differing Sizes of Gaussian Beam Width (x = y)

Beam Spread = 5mm

Beam Spread = 2mm


Irradiation Plan

  • Intend to use existing sensors from ATLAS R&D (made at Micron). Both n- and p- type, Magnetic Czochralski and Oxygenated Float Zone.

  • Plan to assess the bulk damage effects, charge collection efficiency. This will further assess the breakdown on NIEL scaling (x50 at 2 MeV and x4 at 900 MeV) in the energy range of interest.


Sensor +



with Ethernet



Suggestion that p-type bulk may be more resilient (why?) is intruiguing

Need to think about nuclear component: may be dominant source of damage

Believe we are getting close to configuration that will accurately reflect BeamCal sensor conditions

Initial contacts with JLab made; not dismissed (yet…) Much work to do to set up and execute meaningful test run, but shooting for Dec 2010  a few months.


BeamCal Incident Energy Distribution






e+/e- ENERGY (GEV)

BUT: Most fluence is at shower max, dominated by ~10 MeV e-, e+ and . Why might (?) incident energy matter?


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/psistrons)

  • NIEL rises quickly with decreasing (proton) energy, and fragments would likely be low energy

  •  Might small hadronic fractions dominate damage?


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