1. 1 New dividers for LAV photomultipliers G.Corradi,D.Tagnani,C.Paglia, M. Raggi LAV working group CERN 3/2/2010

2. 2 Motivations o o The modification of the divider improves the performance of ToT electronics removing some spurious effect on PMT signal: Ringing of the signal (due to last 3 dynodes inductance) Shoulders of the signal (due to anode disperse inductance) o Clamp of the first dynode rise the potential to 240-250 V Improves the first dynode multiplication factor and therefore total gain Reduce the probability of multiplication starting from 2 nd dynode (lower spread) o Include the 10 K  HV decoupling resistor o Better precision in divider components: Resistors precision 1% (wrt 10% in old divider) Resistors stability 50 ppm (wrt 100 ppm in old divider) Improves gain stability wrt to the one measured during construction

3. 3 Layout First dynode clamp Quenching of d10 d11 d12 and anode Quenching capacitors HV decoupling resistor (10 K  )

4. First dynode clamp 4 o o The voltage drop on the first dynode is generated by 2 diodes 1N4150 in series selected to provide a reverse voltage in the range 120-130 V each o This solution allows us to produce a low noise Zener voltage using low doping in the junction o The differential resistance is on the other hand increased

5. 5 New PCB production status 5 foils 20 dividers each already produced Component mounting is ongoing

6. 6 Printed Circuit Board New “Star” like shaping allows faster positioning of the divider on the dynodes pins

7. 7 PCB components mounting o o Improved thermal stability 50ppm (wrt 100 ppm in old divider) Improved gain stability wrt the one measured during construction o Resistors precision 1% (wrt 10% in old divider)

8. 8 V = -1500 V T amb = 27 °C Air thermal test ΔT = 17 °C I mon = 420μA was (I mon =460 μA) 15% less power consumption wrt old dividers

9. 9 Vacuum test setup The operating P: 4 · 10 -4 - 8·10 -5 mbar Operating voltage: 1500 V Test Duration: 30 h Vacuum window: ZnSe IR Termocamera: Flir E320 The ZnSe window is not fully transparent in the IR spectrum The calibration of the window has been made looking at the same object with and without the window The difference in temperature has been estimated to be 6 °C The calibration has been shown to be stable at different temperatures

10. 10 Vacuum thermal test After 1.5 h @ 1500 V T corr =46.6+6 = 52 C After 2.5 h @ 1500 V T corr = 46.9+6 = 52.9 C After 30 h @ 1500 V T corr =47.5+6 = 53.5 C The value obtained for old dividers was 60 °C. The difference observed is in agreement with the 15% reduction in the divider power consumption

11. 11 Divider discharge test V = -1000V @ T = 27°C Persistency set to 5 minutes V= -1500V @ T = 27°C Persistency set to 5 minutes

12. 12 Cosmic ray signals V = -1400 V 10 mV vertical scale  V = -1400 V  50 mV vertical scale

13. 13 HV divider quality test Tested on 5 different dividers; Maximun non linearity = 1% Vg = -500V

14. 14 Conclusions o o Mounting of the divider is very fast (5 to 10 minutes/PMT) o First HV test 2500V for 1 min did’nt shown any discharge o Power consumption reduced by 15%, operating temperature in vacuum reduced (from 60°C to 54°C) o Resistors stability 50ppm (was 100ppm) o Resistors precision 1% (was 10% ) o Divider non linearity below 1% o Spread of dividers characteristics is around 2%, negligible wrt intrinsic gain spread of PMTs