Specification for broad-band tagging hodoscope
In its standard configuration the fixed-array hodoscope consists of 218 scintillators distributed over 9.1 m behind the focal-plane of the tagger spectrometer. Standard configuration refers to a coherent-peak setting at 9.0 GeV, i.e. the microscope covers the energy range 8.1<Eγ<9.1 GeV.
Tagging range (for a 12 GeV electron beam):
- Photons between 3.0 GeV and 8.2 GeV: detector positions correspond to 60 MeV steps in Eγ with 30-50% sampling. The counter widths are chosen such that the typical rate per counter is limited to 3-4 MHz at 108 γ/sec on target;
- Photons between 9.2 GeV and 11.78 GeV: scintillators cover the full energy range, counter widths were calculated such that the typical rate per counter is limited to 1-4 MHz at 108 γ/sec on target.
All counters will be mounted at angles such that they face normal to the path of the scattered electrons.
All light guides (UVT PMMA) have cylindrical shape of 120 mm length and 7/8" = 22.2mm diameter to cover the size of the photocathode. A collar at 60mm height with 2 bolts along the slot line ensure proper positioning of the counters: threaded holes for the bolts in the mounting plates are correspondingly oriented.
Hamamatsu R9800: 1" tube with 8 dynodes, rise time 1.0 ns, transit time 11 ns, 27% quantum eff., max. anode current 100 μA.
magnetic shields: μ-metal cylinders.
HV dividers and 2-stage preamps (amp. factor 8.5x) developed at Jefferson Lab, they allow for limiting the anode current to 15-20 μA at 4 MHz rate.
Operating voltage: U=900 V resulting in a gain of 5×105, anode current contributes to less than 5% of the active base current.
Readout electronics The new preamp boards have 2-channel output for fADC250 and F1TDC.
Fixed array counter positions
Table moved to Position and Energy Boundaries for all installed Counters