Status of the Tagger Hall Background Simulation Simulation A. Somov, Jefferson Lab Hall-D Collaboration Meeting, University of Regina September

Analysis 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

Tagger Hall and Beam Dump Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September Z (cm) X (cm) Goniometer Quadrupole 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 Geometry Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September 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)  Position of 12 GeV electrons at beam monitors:  Magnet poles

Downstream end of Vacuum Chamber & Electron Pipe Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September Z (cm) X (cm) Detector plane 9 GeV electrons 12 GeV electrons Vacuum Chamber Rectangular Beam Pipe 1  + 3  = 4  wide Flange End of exit window

Simulation Overview Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September  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 ~10 13 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 Neutrons Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September Z (cm) X (cm) Vacuum chamber flange Electron Pipe Tagger Hall walls Magnet poles Air

Neutron Energy Spectrum at the Detector Plane Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September Neutron kinetic energy ( MeV ) Biological damage coefficients Neutron energy spectrum pSv cm 2

Neutron Dose Estimates (preliminary) Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September Z (cm) Events Neutron distribution along the focal plane 3  pipe: 0.6 rem/hour 6  pipe: 0.46 rem/hour Microscope counters region: 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 Plans Status of the Tagger Hall Background Simulation, Hall-D Collaboration Meeting, September  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 ….