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

Tagger hodoscope and Tagger hodoscope and photon beam monitoringphoton beam monitoring

D.Sober, F.Klein (CUA)

Tagger Review, Jan.23-24, 2006

Hall-D taggerHall-D tagger• two-magnet design• horizontal deflection• photon spectrum:coherent and incoherent

bremsstrahlung

deflected e-beamdeflected e-beam

primary e-beamprimary e-beam

Coherent Bremsstrahlung Coherent Bremsstrahlung in Hall Bin Hall B

data taking at E0=4-6 GeVcoh. peak at 1.3-2.2 GeV50μm (20μm) diamonds (mosaic spread<10μrad)

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Coh.peak at 2.1 GeV

Coh.peak at 1.5 GeV

Coh.peak at 1.3 GeV

Crystal alignmentCrystal alignment

Hall-B goniometer (6 d.o.f.)for crystal positioning

Hall-B alignment via“Stonehenge” method:

Hall-D tagging systemHall-D tagging system

• Beam energy E0=12 GeV• coherent peak at 7-10 GeV• microscope tags ~600 MeV near coh. peak• fixed hodoscope (tags 3.0-11.4 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 θchar

• microscope tags 9.0-9.6 GeV– 25 MHz tagged photons in microscope– 10 MHz tagged photons on target

(40% collimation)

Rate estimates (2)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:Proposal for fixed array:

• 140 counters at 60 MeV (0.005 E0) 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)

Eγ (GeV)tag rate

(kHz/MeV)counter width sample fraction

(at 60MeV spacing)

counting rate(at 10MHz on target)

3.0 80 0.28 cm 0.42 ~2 MHz

4.0 60 0.39 cm 0.55 ~2 MHz

5.0 50 0.50 cm 0.67 ~2 MHz

6.0 45 0.58 cm 0.73 ~2 MHz

7.0 40 0.73 cm 0.83 ~2 MHz

8.0 40 0.81 cm 0.83 ~2 MHz

9.0 – 11.4(above coh. peak)

22 – 26 1.1 – 3.7 cm 1.0 ~1.4 MHz

Fixed array:Fixed array:Sampling at lower energiesSampling at lower energies

purpose: alignment (not used during production runs)

option to insert additional counters later

Relative intensityRelative intensity

crystal alignment with 60 MeV sampling full coverage

photon energy (MeV)photon energy (MeV)

Fixed array:Fixed array:Sampling at lower energies (2)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:Fixed array:full coverage in endpoint regionfull 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 width rate at 10 MHz tags on target

rate at 100 MHz tags on target

40 60 MeV 1.1 – 3.7 cm 1.4 MHz 14 MHz

80 30 MeV 0.6 – 1.8 cm 0.7 MHz 7 MHz

120 20 MeV 0.4 – 1.2 cm 0.5 MHz 5 MHz

Fixed tagging hodoscope for Hall D:

purpose:

Option: Monitoring of collimated photon beam via pair spectrometer

SummarySummary

• 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: