1. Quartz Detectors for the SuperHMS Spectrometer A
Quartz Detectors for the SuperHMS Spectrometer A. Ahmidouch, NC A&T Jlab Hall C EER, Aug , 2016
Quartz detector S2Y  trigger system. Major change from
the standard HMS hodoscope design
Hodoscope S2 Placed at +265 cm from the focal plane,
in front of the Lead-Glass calorimeter
Needed to:
Provide a clean detection of charged particles
2. Provide a high level of background rejection
3. Provide accurate tracking efficiency determination

2. Quartz Hodoscope

3. Beam envelope: X(-55,60cm) and Y(-50,55cm) 21 quartz bars: ( ) x 5.5 x 2.5 cm3 , with 0.5 cm overlap

4. Detection in Quartz Bar
Index of refraction n =
Cerenkov light, TIR
cos(q) = 1/b n, 47 deg.
Threshold velocity, bth = 0.68

5. Corning 7980 Performance Properties: UV transparent radiation hard*
low luminescence
Requirement:
- Optical uniformity: optical grade polish 25 A rms, flatness 200 mm
Corning 7980 transmission
n-l dependence

6. Radiation Hardness: Transmission measurements From NIM A 595 (2008) 190
DT = (Tbefore - Tafter) / Tbefore

8. Quartz Bar Length: 125 cm Width: 5.5 cm Thickness: 2.5 cm
No lightguide
PMT: 2-in Photonis XP2020
or ET 9814QB
2.5 cm for holding
2.5 cm mu-metal

9. Detector Layout 21 quartz bars 0.5 cm overlap Covers area:
105.5 x 115 cm2
Top view
Quartz-PMT attachment
Frame built by W&M

10. PMTs 18 ET 9814QB PMTs operated in positive polarity.
24 Photonis XP2020Q

11. Quartz bar – PMT optical coupling
Use of Silicone rubber compound
RTV615A
High strength silicon gel
Cures at room temperature
n = 1.406
Retains elastometric properties at
T < 204 0C
Transparency measurements

12. 0.8-1.0 mm layer of gel is let to cure for ~8 hrs
PMTs are then coupled to quartz bars

13. Testing and Calibrationm

14. Set up for Testing

15. ADC histograms
Npe ~ 20

16. Position measurements

17. Position reconstructed vs actualcm
sposition = 1.3 cm

18. Position reconstruction possible with 1 TDC only

19. Summary-1 21 quartz bars were constructed and delivered to Jlab
PMT to quartz attachment
 Use of removable bracket
Optical coupling  silicon gel
Excellent position resolution
 ~ 1.5 cm
light yield ~20 pe

20. Test of PMTs at JLab, problem w/ Photonis tubes
Most 24 XP2020Q PMTs trip while under HV
The performance of the tubes degraded over time as they were kept
under high voltage and tested
Three XP tubes have been removed for investigation;
checked for He poisoning (LED test to look for afterpulsing)
and for possible physical damage

21. Test of PMTs at JLab (cont’d)
The 18 ET-9814QB PMTs are stable and do not trip – must operate within nominal gain 3x107
Will LED test a few ET PMTs to make ensure stability under
load of experiments

22. Summary-2 and Recommendations
XP PMTs became deficient and need to be replaced.
Purchase new ET PMTs or Hamamatsu R2059
order by 10/01/2016
PMT Delivery, weeks
Check PMTs vs. specs, + 1 week
Attach PMTs to bars, + 2 weeks
Test detector performance, + 3 weeks