Tagger hodoscope and photon beam monitoring D.Sober, F.Klein (CUA) Tagger Review, Jan.23-24, 2006

Hall-D tagger two-magnet design horizontal deflection photon spectrum: coherent and incoherent bremsstrahlung deflected e-beam primary e-beam

Coherent Bremsstrahlung in Hall B data taking at E 0 =4-6 GeV coh. peak at GeV 50μm ( 20μm) diamonds (mosaic spread<10μrad) Enhancement (after collimation) Coh.peak at 2.1 GeV Coh.peak at 1.5 GeV Coh.peak at 1.3 GeV

Crystal alignment Hall-B goniometer (6 d.o.f.) for crystal positioning Hall-B alignment via “Stonehenge” method:

Hall-D tagging system Beam energy E 0 =12 GeV coherent peak at 7-10 GeV microscope tags ~600 MeV near coh. peak fixed hodoscope (tags GeV) –located 20 cm from true focal plane (to allow for microscope motion) Requirements for fixed hodoscope: crystal alignment → special runs at reduced rate photon beam monitoring → at full production rate

Rate estimates (1) Rate estimates (1) assuming: Jlab beam conditions 20μm crystal coh. peak at 9.6 GeV collimation to 0.56 θ char microscope tags GeV –25 MHz tagged photons in microscope –10 MHz tagged photons on target (40% collimation)

Rate estimates (2) Rate per cm counter width full energy range Note: Structures above 10.5 GeV washed out due to dispersion high energy range

Proposal for fixed array: 140 counters at 60 MeV (0.005 E 0 ) steps full coverage: 9.0 – 11.4 GeV (40 counters at 60 MeV spacing) sampling: 3.0 – 9.0 GeV (100 counters at 60 MeV spacing) E γ (GeV) tag rate (kHz/MeV) counter widthsample fraction (at 60MeV spacing) counting rate (at 10MHz on target) cm0.42~2 MHz cm0.55~2 MHz cm0.67~2 MHz cm0.73~2 MHz cm0.83~2 MHz cm0.83~2 MHz 9.0 – 11.4 (above coh. peak) 22 – – 3.7 cm1.0~1.4 MHz

Fixed array: Sampling at lower energies purpose: alignment (not used during production runs) option to insert additional counters later Relative intensity crystal alignment with 60 MeV samplingfull coverage photon energy (MeV)

Fixed array: Sampling at lower energies (2) problem to analyze spectra when sampling? structures less pronounced esp. difficult when crystal far off-axis – but feasible with ~50-60 MeV sampling crystal alignment with 60 MeV sampling full coverage (raw) full coverage (analyzed)

Fixed array: full coverage in endpoint region Purpose: alignment of diamond crystal monitoring of structures during production runs options for high rates: number of counters energy bite per counter counter widthrate at 10 MHz tags on target rate at 100 MHz tags on target 4060 MeV1.1 – 3.7 cm1.4 MHz14 MHz 8030 MeV0.6 – 1.8 cm0.7 MHz7 MHz MeV0.4 – 1.2 cm0.5 MHz5 MHz

Fixed tagging hodoscope for Hall D: purpose: Option: Monitoring of collimated photon beam via pair spectrometer Summary monitoring of photon beam crystal alignment full coverage at 9.0 – 11.4 GeV sampling at 3.0 – 9.0 GeV (60MeV momentum bites) option to add counters for full coverage (at lower production rates) scintillation counters (0.5 cm thick, 4 cm high) width: 0.28 – 3.7 cm (adjusted to rates of ~2 MHz/counter for 10 MHz on target) proposal:

Pair Spectrometer positioned downstream of instrumented collimator left-right coincidence (~12–16 counters each side) relative flux monitoring of collimated photon beam (~600 MeV around coherent peak) backup

120MeV Sampling 120MeV sampling ? cheaper – but: → not enough coverage to identify structures backup