Status of the Tagger Hall BackgroundStatus of the Tagger Hall Background SimulationSimulation
A. Somov, Jefferson Lab
Hall-D Collaboration Meeting, University of Regina September 9 2010
Analysis OverviewAnalysis Overview
Update Tagger Hall Geant geometry
- narrow dipole magnet (new magnetic field map) - smaller vacuum chamber ( ~ 1.5 m shorter ) - new position of the focal plane and detectors - realistic geometry for the electron beam dump
Study neutron background at the detector plane ( SiPM radiation hardness )
- use Radiation Control Geant 3.21 simulation provided by Pavel Degtyarenko - compare neutron doses with FLUKA
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 2
Tagger Hall and Beam DumpTagger Hall and Beam Dump
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 3
Z (cm)
X (
cm)
GoniometerQuadrupole Magnet
Dipole Magnet
Vacuum Chamber
Labyrinth Wall 1
Lab Wall 2 Lab Wall 3
Beam Dump
e - Beam photons
Detector plane
• Deflection angle for 12 GeV electrons: 13.4• Magnet rotation: 6.5• Focal plane angle: 8.05
Tagger Hall GeometryTagger Hall Geometry
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 4
Possible sources of background:
Flange of the vacuum chamber
Electron beam pipe
Flange
Electron pipe
Z (cm)
X (
cm)
Dipole magnet cross-section (X-Y plane)
3 cm gap
12GeV electrons
Z (cm) X (cm)
2630.1 -475.8
2649.7 -480.4
2785.8 -512.9
Position of 12 GeV electrons at beam monitors:
Magnet poles
Downstream end of Vacuum Chamber Downstream end of Vacuum Chamber & Electron Pipe& Electron Pipe
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 5
Z (cm)
X (
cm)
Detector plane9 GeV electrons
12 GeV electrons
Vacuum Chamber
Rectangular Beam Pipe
1 + 3 = 4 wide
Flange
End of exit window
Simulation OverviewSimulation Overview
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 6
Estimated neutron background originating in the Tagger Hall and the beam dump enclosure. Particles were ‘stopped’ before the dump, more CPU is needed ( high-luminosity corresponds to ~1013 electrons/sec; 1 event – 0.4 sec)
- determine neutron flux and energy spectrum of neutrons at the focal plane: L = 852 cm, h = 100 cm
- use biological damage conversion curve to estimate neutron dose
Note: To estimate radiation damage, we have to use effective damage curve of Si (to be done). The neutron energy spectrum looks ‘similar’ to that used by Yi in his studies can use his numbers to estimate the dark rate increase Study background for 2 widths of the electron pipe: 3 and 6 between full energy electrons and the pipe walls
Origin of NeutronsOrigin of Neutrons
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 7
Z (cm)
X (
cm)
• Vacuum chamber flange• Electron Pipe• Tagger Hall walls• Magnet poles• Air
Neutron Energy Spectrum at theNeutron Energy Spectrum at theDetector PlaneDetector Plane
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 8
Neutron kinetic energy ( MeV )
Biological damage coefficients
Neutron energy spectrum
pS
v cm
2
Neutron Dose Estimates (preliminary)Neutron Dose Estimates (preliminary)
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 2
Z (cm)E
ven
ts
Neutron distribution along the focal plane
3 pipe: 0.6 rem/hour
6 pipe: 0.46 rem/hour
Microscope countersregion: 0.2 rem/hour
According to Yi’s studies the dark current increases by a factor of 5 for the accumulated dose of 60 rem
Further studies/geometry optimization is neede – work in progress
Further PlansFurther Plans
Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting , September 9 2010 2
The first studies indicate large neutron background at the detector plane
We have to check Geant geometry and ‘optimize’ layouts of the electron beam pipe and the downstream flange of the vacuum chamber
- use a window or low density material for the beam pipe wall …
Check Pavel Degtyarenko’s Geant with FLUKA (work in progress) We need to develop a plan to use other detectors instead of SiPM’s if the neutron background appears to be really high….