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