Difference between revisions of "Specification for broad-band tagging hodoscope"

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The fixed-array hodoscope consists of 180 scintillators distributed over a length of 11.2 m at a distance of 30 cm from the focal plane of the two-magnet system.  
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[[Image:TAGH-from-magnet-all.jpg|900px|]]
 +
 
 +
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&lt;E<sub>&gamma;</sub>&lt;9.1 GeV.  
  
 
Tagging range (for a 12 GeV electron beam):  
 
Tagging range (for a 12 GeV electron beam):  
* <b>Photons between 3.0 GeV and 9.0 GeV</b>: detector positions correspond to 60 MeV steps in E<sub>&gamma;</sub> with <b>50% sampling</b>, i.e. the counter widths correspond to 30 MeV bites resulting in ~0.8-1.1 MHz per counter at 10<sup>7</sup> &gamma;/sec on target;  
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* <b>Photons between 3.0 GeV and 8.2 GeV</b>: detector positions correspond to 60 MeV steps in E<sub>&gamma;</sub> with <b>30-50% sampling</b>. The counter widths are chosen such that the typical rate per counter is limited to 3-4 MHz at 10<sup>8</sup> &gamma;/sec on target;  
* <b>Photons between 9.0 GeV and 11.4 GeV</b>: detector positions correspond to 30 MeV steps in photon energy resulting in ~400 kHz per counter at 10<sup>7</sup> &gamma;/sec on target.
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* <b>Photons between 9.2 GeV and 11.78 GeV</b>: scintillators cover the full energy range, counter widths were calculated such that the typical rate per counter is limited to 1-4 MHz at 10<sup>8</sup> &gamma;/sec on target.  
Count rates in the high-energy range allow for operation at 10<sup>8</sup> &gamma;/sec on target.  
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All counters will be mounted at angles such that they face normal to the path of the scattered electrons.  
 
All counters will be mounted at angles such that they face normal to the path of the scattered electrons.  
  
 
'''Scintillators'''
 
'''Scintillators'''
  
      thickness        5mm
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<table width="100%">
      length          30mm
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<tr><td width="70%">
      width (quantity) 30(2), 25(3), 20(6), 15(15), 10(14),
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{|
                      8(13), 7(9), 5(54), 4(24)
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| Material
 +
| EJ-228
 +
|-
 +
| Thickness &nbsp; &nbsp;
 +
| 6 mm
 +
|-
 +
| Height
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| 40 mm (slotted into the light guides, slot depth: 3mm)
 +
|}
  
 +
 +
{| border="1" style="text-align:center;" cellpadding="10" cellspacing="0"
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|- style="font-style:bold; color:blue;"
 +
|!scope="row" | Counter # || width <br>[mm] || distance from <br>focal plane || E<sub>&gamma;</sub> <br>[GeV] || &Delta;E <br>[MeV]
 +
|-
 +
| 1 – 22 || 21.0 || 8 / 18 cm  || 11.43 – 11.78 || 10.2 – 23.7
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|-
 +
| 23 – 40 || 16.0 || 8 / 18 cm || 11.01 – 11.43 || 18.4 – 29.5
 +
|-
 +
| 41 – 64 || 10.0 || 8 / 18 cm || 10.46 – 11.01 || 18.7 – 26.8
 +
|-
 +
| 65 – 81 || 8.0 || 8 / 18 cm || 10.05 – 10.46 || 21.7 – 26.0
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|-
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| 82 – 139 || 5.0 || 8 / 13 / 18 cm || 9.20 – 10.05 || 16.4 – 22.2
 +
|-
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| 140 – 195 || 4.0 || 8 / 13 / 18 cm || 7.07 – 8.13 || 16.6 – 17.2
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|-
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| 196 – 274 || 3.0 || 8 cm || 3.05 – 7.03 || 13.7 – 20.3
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|}
 +
 +
</td>
 +
<td> &nbsp; &nbsp; &nbsp; [[Image:TAGH-counter-cut.jpg|100px|]]
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</td>
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</tr>
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</table>
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 +
'''Light guides'''
 +
 +
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.
 +
 
'''Photomultipliers'''
 
'''Photomultipliers'''
  
      1" tubes with magnetic shields
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Hamamatsu R9800: 1" tube with 8 dynodes, rise time 1.0 ns, transit time 11 ns, 27% quantum eff., max. anode current 100 &mu;A.<br>
 +
magnetic shields: &mu;-metal cylinders.<br>
 +
HV dividers and 2-stage preamps (amp. factor 8.5x) developed at Jefferson Lab, they allow for limiting the anode current to 15-20 &mu;A at 4 MHz rate.<br>
 +
Operating voltage: U=900 V resulting in a gain of 5&times;10<sup>5</sup>, anode current contributes to less than 5% of the active base current.
  
 
'''Readout electronics'''
 
'''Readout electronics'''
      CFDs, TDCs, Scalers
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The new preamp boards have 2-channel output for fADC250 and F1TDC.
 +
 
 +
 
  
'''Resolution'''
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==Fixed array counter positions==
  
      timing:  rms ~100-150 psec
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Table moved to [[Position and Energy Boundaries for all installed Counters]]
      energy:  20 MeV (above 9.0 GeV photon energy)
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              30 MeV (sampled - below 9.0 GeV photon energy)
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Latest revision as of 20:00, 25 January 2017

TAGH-from-magnet-all.jpg

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.

Scintillators

Material EJ-228
Thickness     6 mm
Height 40 mm (slotted into the light guides, slot depth: 3mm)


Counter # width
[mm]
distance from
focal plane
Eγ
[GeV]
ΔE
[MeV]
1 – 22 21.0 8 / 18 cm 11.43 – 11.78 10.2 – 23.7
23 – 40 16.0 8 / 18 cm 11.01 – 11.43 18.4 – 29.5
41 – 64 10.0 8 / 18 cm 10.46 – 11.01 18.7 – 26.8
65 – 81 8.0 8 / 18 cm 10.05 – 10.46 21.7 – 26.0
82 – 139 5.0 8 / 13 / 18 cm 9.20 – 10.05 16.4 – 22.2
140 – 195 4.0 8 / 13 / 18 cm 7.07 – 8.13 16.6 – 17.2
196 – 274 3.0 8 cm 3.05 – 7.03 13.7 – 20.3
      TAGH-counter-cut.jpg

Light guides

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.

Photomultipliers

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