LAV construction & installation status

1. LAV construction & installation status Matthew Moulson for the LAV Working Group NA62 Photon-Veto Working Group Meeting CERN, 17 December 2013

2. LAV installation status at a glance • A10 transport 15-16 October • Last transport for LAV stations in vacuum • No damage – relatively uneventful • Separate transport to be organized to return endcaps to Fantini • Unable to transport all 4 endcaps on return trip • 2 endcaps currently in use – need to replace with wooden endcaps • A9 installation week of 04 November • Waiting to install A10-A11 – new pieces of blue tube in stainless steel won’t be ready until March 2014 • Cabling work • Installation of cable supports for A6-A7-A8 • Measurements for cable supports for A9-A10-A11 • HV cabling: A4-A8 + recabling of A1-A3 with reflected cables • Small modification needed for new cables • Waiting for signal cables for A1-A11 with correct impedance to be manufactured

3. A10 transport No acceleration events No damage • Temperature not as stable as in other transports • Less efficiently wrapped? • Thermal blanket setting too low?

4. A12 construction status at a glance 263 blocks of Type 8 glued 300 HV dividers ready (143 with cables)

5. Setup for wrapping & light-leak testing cleaning stand oscilloscoppio block to test light source HV scaler LTD amp

6. Notes on setup of electronics • Lead-glass blocks: • MD8090: dyMat T wrapping from A4 sample sheets • ME1739: dyMat T wrapping from single sheet, separate end piece • ME3301: dyMat T wrapping from single sheet, end flap • Fast amplifier: • CAEN N412: 8 channels, fixed 10× gain • Low-threshold discriminator: • LeCroy 620AL: 8 channels with −30 mV to −1 V common threshold • Scaler: • CAEN N1145: 4 channels + timer • HV supply: • CAEN N470: 4 channels, 3kV × 3mA, configurable polarity, front-panel programmable

7. Noise problems in Ed. 57 • RF noise in Ed. 57: • Frequency ~100 MHz • Modulated at ~2.5 MHz • Amplitude 11-19 mV • Variable in time • Significant complication for light-tightness mmt: • Light leaks give small (< 10 mV) pulses • Noise appears to be induced: • Complete shielding e.g. of HV divider with Al foil reduces noise ~30% • Not effective enough • In practice, difficult to shield HV divider on block anyway 10 mV × 50 ns −12.5 mV trig 10 mV × 2 μs −12.5 mV trig

8. Low-pass RC filter for noise Since we cannot eliminate noise by grounding or shielding, try to see if we can filter it Since the PMT is approximately a current source, use a parallel RC circuit as a simple low-pass filter I R C V At low f, V = IR At high f, V < IR dV dt V = IR − RC

9. Effect of filter on signal and noise Test pulse, no filter: 50 ns × 50 mV Noise, no filter: 50 ns × 10 mV Test pulse: 100 mV 5 ns rise, 15 ns fall 20 ns duration trig −95 mV offset −4 mV trig −11.8 mV Test pulse, filter: 50 ns × 20 mV Noise, filter: 50 ns × 2 mV trig −40.2 mV offset −4 mV trig −2.48 mV Test pulse attenuation = 0.40 Noise attenuation = 0.21 S/B increased 1.92× Can trigger at 3 mV with filt (= 7.5 mV)

10. Effect of amplification on noise Noise, before amp: 50 ns × 10 mV Noise, amp 10×, filter: 50 ns × 20 mV trig −17 mV offset +10 mV trig −19 mV Noise, amp 10×: 50 ns × 100 mV After amplification: Noise attenuation = 0.21 → 0.11 Possibly from better measurement, though effect seems to be real trig −236 mV

11. Threshold setting for production Signal from tube, with filter: 50 ns × 10 mV 50 ns × 10 mV −2.5 mV trig • Can easily trigger at 2.5 mV, with great sensitivity to light pulses • Include 10x amplifier in signal chain • LTD threshold set to 25 mV using test pulse (= 0.237 V on monitor pin)

12. dyMat T wrapping: Initial observations • Test stand offers good sensitivity to light leaks • Well-wrapped block counts at 100-1000 Hz before debugging • Counts skyrocket when flashlight shines on defects in wrapping • With careful application of black tape, count rate can be brought to ~1 Hz and does not change when block wrapped in black cloth • dyMat T wrapping is generally effective at blocking light • Intact wrapping blocks light from 100 W incandescent bulb at 40 cm • Sealing technique around reinforcement plates appears to be effective: • Inner layer of black tape directly on reinforcement plates • Outer layer of black tape to seal wrapping to inner layer • Black outer coating is somewhat fragile • Scratches or dimples that appear white to the eye will transmit light and must be repaired by application of black tape • Edges and corners are particularly vulnerable and will need to be reinforced a priori with black tape

13. Examples of scratches and scuffs Sharp object pressed into outer layer of wrapping, causing depression Scuff marks scrape off black outer layer Ding along edge of block

14. Corners require special care • Corners susceptible for two reasons: • Cracks originating from folds in wrapping • Damage from handling • No significant difference between wrapping patterns • End flap vs separate end piece) • Operative rule: • Any white spots in wrapping must be covered!

15. Thoughts on wrapping procedure • Blocks are heavy – need to minimize handling: • Efficiency: Repeated movements take time and effort • Protection of wrapping: More movements = more damage • Ergonomics & safety! • Reduce number of necessary movements by testing blocks in oven before wrapping: Add new HV divider Move to cleaning stand; clean and wrap Move to oven and test Move to cleaning stand and test for leaks Move to A12 and mount Add new HV divider Move to oven and test with original wrapping Move to cleaning stand; clean and wrap block and test for leaks Move to A12 and mount • Save 1 movement overall and 2 movements with new wrapping • Of course, must confirm that results in oven same with old/new wrapping

16. Comparison of old & new wrapping Initial comparison of oven results from two blocks with original and new wrapping gives encouraging results Need to repeat test with higher statistics when wrapping material arrives

17. Thoughts on rapid light-leak testing • Need a standard test for light leaks that is: • Reliable – passing test indicates that block is sufficiently light tight • Reproducible – same test applied over and over gives same results • Rapid – have to process many blocks • In addition, desirable for test to supply some information on location of leaks • Leaks can be very small and are best found with small flashlight • Very helpful if standard test provides general area for light leaks • Idea is to use a lightweight wooden box with LED distributed over internal surface to illuminate all sides simultaneously • Can be used two ways: • Block suspended from cleaning stand – light box pulled up from below • Block stood tube-down on table – light box lowered over block • LEDs on each internal face independently switchable to provide some ability to localize leaks • Leaks can also be localized by lowering/raising box slowly over block and watching count rate

18. Design notes for light box Light source: 300 parallel wired LEDs in 5 m of transparent, waterproof (IP65), epoxy-based strip with adhesive backing • SMD 3528 LEDs (3.5 × 2.8 mm2) • Brilliant white (6000K) • 300 LED = 1560 lumen • (100 W incandescent = 1380 lumen) • Power consumption at 12 VDC: • 4.8 W/m rated • 3.8 W/m measured • Design considerations: • Volume 24 × 24 × 60 cm3: completely covers block, including PMT • Lightwight aspen plywood construction + 2 handles for easy handling • Interior spray painted with opaque white enamel • All wiring on exterior – nothing to snag or catch on inside • LED strips are soft, rubbery epoxy

19. Light box (“Discoteca”) Thanks to G. Petragnani for help with design & construction!

20. Sides are independently switchable

21. Summary • Installation status: • A10 transported to CERN in October – A1-11 have all been delivered • A9 has been installed – A1-9 have all been installed • Cabling work is in progress • Status of wrapping and light-leak tests for A12: • We know we can get a good, light-tight wrapping with dyMat T • We have developed a reliable technique for measuring light-leak rates • We still need to optimize and streamline the procedure for wrapping and testing, especially to avoid excessive handling • We have taken steps in this direction: • We will investigate the feasibility of testing in oven before wrapping • Preliminary indications are that this makes no difference • We have developed a convenient standard illumination source (“Discoteca”)