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Forward Tagger Simulations. New geometry Moller Shield Acceptance Background rates and dose. R. De Vita INFN – Genova Forward Tagger Meeting, CLAS12 Workshop, November 10 2010. New Geometry. FT support material changed to tungsten to improve radiation containment Outer case added

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forward tagger simulations

Forward Tagger Simulations

New geometry

Moller Shield


Background rates and dose

R. De Vita

INFN –Genova

Forward Tagger Meeting, CLAS12 Workshop, November 10 2010

new geometry
New Geometry
  • FT support material changed to tungsten to improve radiation containment
  • Outer case added
  • Inner beamline modified to shield small angle crystals from beam halo
  • 408 crystals
  • 15x15x200 mm size
  • Coverage from 1.8 to 5.2 deg.
  • Tungsten beam pipe to shield from beam halo

tungsten case


beamline to torus

shield for inner crystals

back flange

moller electrons and beam halo
Moller Electrons and Beam Halo
  • The Moller shield was designed studying the transverse size of the beam halo and the Moller electrons distribution
  • The moller spot is always larger than the size of a 2 deg cone
  • A 2.5 deg. cone can contain most of the background
  • Optimal z of the cone entrance is at 75 cm from the target

z=50 cm

z=75 cm

All particles


Moller electrons

Moller electrons E>200 MeV



The lines indicate the size of a cone with 2 deg. and 2.5 deg. aperture

z=100 cm

dc occupancy test of standard clas12 shield geometry
DC Occupancy: test of standard CLAS12 shield geometry

To check reliability of the DC occupancy estimate, the standard CLAS12 Moller shield geometry (optimized by A. Vlassov) was implemented in GEMC

The shield consists of an aluminum/tungsten cone with max. angle of ≈4 deg.

Most of the background hitting the DC consist of photon coming from the target region

Typical occupancies are of the order of 1%

dc occupancy ft moller shield
DC Occupancy: FT Moller shield
  • A shield compatible with the FT geometry and acceptance was designed based on a single tungsten cone
  • entrance at z=75 cm
  • outer angle: 2.45 deg
  • inner diameter: 60 mm

DC Occupancy is <2.5% in R1 and <1% in R2,R3

Improvement is possible with further optimization of the Moller shield

electron detection and a cceptance
Electron detection and acceptance

Electrons in the energy range 0.5-4.5 GeV and angular range 1-35 deg. were simulated to study the characteristic of the signal induced in the calorimeter and check the acceptance

background rates
Background Rates
  • Background on the calorimeter due to the beam was simulated generating electrons 10 cm upstream to the target
  • the energy deposited per ns is <0.3 MeV
  • the particles with =0.5-4.5 GeV hitting the FT are a mix of electrons, photons and hadrons
  • the overall rate is of about 48 MHz
  • the rate of particles with E=0.5-4.5 GeV is ≈180 KHz
radiation dose
Radiation Dose

The corresponding dose on the single crystals is less than 5 rad/h and less than 2 rad/h excluding the innermost crystals (not necessary for detection of electron above 2.5 deg)

This dose is compatible with the operation of LeadTungstenwithour significant deterioration of light transmission properties

work plan for proposal and beyond
Work Plan for Proposal and Beyond
  • For the proposal:
  • repeat background rates evaluation using cluster algorithm
  • complete study of signal/background separation
  • Long term plan:
  • continue optimization of Moller shield and FT geometry
  • complete implementation of calorimeter reconstruction (cluster algorithm