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….