Quartz Detectors for the SuperHMS Spectrometer A Quartz Detectors for the SuperHMS Spectrometer A. Ahmidouch, NC A&T Jlab Hall C EER, Aug. 24-25, 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

Quartz Hodoscope

Beam envelope: X(-55,60cm) and Y(-50,55cm) 21 quartz bars: (115+5+5) x 5.5 x 2.5 cm3 , with 0.5 cm overlap

Detection in Quartz Bar Index of refraction n =1.45-1.56 Cerenkov light, TIR cos(q) = 1/b n, 47 deg. Threshold velocity, bth = 0.68

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

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

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

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

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

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

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

Testing and Calibration m

Set up for Testing

ADC histograms Npe ~ 20

Position measurements

Position reconstructed vs actual cm sposition = 1.3 cm

Position reconstruction possible with 1 TDC only

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

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

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

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, +8-10 weeks Check PMTs vs. specs, + 1 week Attach PMTs to bars, + 2 weeks Test detector performance, + 3 weeks