1. Forward Tagger Simulations
New geometry
Moller Shield
Acceptance
Background rates and dose
R. De Vita
INFN –Genova
Forward Tagger Meeting, CLAS12 Workshop, November

2. 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
crystals
beamline to torus
shield for inner crystals
back flange

3. GEANT4 Simulations

4. 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
Electrons
Moller electrons
Moller electrons E>200 MeV
Photons
Others
The lines indicate the size of a cone with 2 deg. and 2.5 deg. aperture
z=100 cm

5. 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%

6. 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

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

8. 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 = 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= GeV is ≈180 KHz

9. 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 LeadTungsten withour significant deterioration of light transmission properties

10. 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 …