1

HERSCHEL: PMT status report

• The order to replicate PCB for divider of R1828-01 has been launched on 11-02-2014a) digital file for production (promised by 14-03-2014)b) production of PCB (not started, on critical path)

• Prototype base modifications a) old base like for BLS counters (ready, waiting for R1828 delivery

2pieces)b) new base for modified voltages sequence (waiting for ordered components -

FARNELL)

• Stand for study of PMTs with LEDsa) pulsing LED with signal recording (in use, scope LeCroy WaveRunner

104MXi-A)b) permanent illuminating LED (scheduled for coming week-end)

• Cosmic stand with prototype counters and PMTsa) trigger counters (ready) b) prototype counters (to be assembled during next

week - Raphael)c) oscilloscope “LeCroy WR 104MXi-A” (ready – 350CHF/month)

• Two LEDs to be embedded inside scintillator – transparency monitoring!(to be checked with prototype)

• 30 old PMTs “56AVP” available from UA1 thanks to Raphael and Heinrich!!!

• Extensively checked last few days (first results available)

RD 21/03/2014

2

HERSCHEL: PMT status report

RD 21/03/2014

STAND for PMT TESTS with LEDs

• base for test R1828

• old resistive base for 56AVP (UA1)

• scope LeCroy WR 104MXi-A (1GHz, 4 ch., WindowsXP )

• NIM crate with LED driver and trigger logic

•HV power supply and current monitoring

All 30 PMTs “56AVP” passed check :

• all are alive and working

• relative photocathode quantum efficiency measured

• Gain = A (HV) α measured to be ~12.2

3

HERSCHEL: PMT status report

RD 21/03/2014

STAND for COSMIC TESTS

Prototype scintillator counter

4

HERSCHEL: PMT status report

RD 21/03/2014

Two LEDs allow plastic transmittance monitoring

LED – 1 LED – 2

Aim – to monitor ratio LED1/ LED2 during shut-down

Vacuum pipe

5

HERSCHEL: PMT status report

RD 21/03/2014

OLD PMTs from UA1

For the same LED brightness and HV=1850V the response varies from

min - 35mVmax – 729mV

All 30 “56AVP” are alive – responding to LED pulse.

6

HERSCHEL: PMT status report

RD 21/03/2014

OLD divider from UA1

• Magnetic steel shielding with 2 LEDs on top

• Mu-metal screening

• Electro-static screening @photocathode HV

• Pure resistive divider

Average pulse height .vs. HV (two LED intensity settings)

56AVP #22544

7

HERSCHEL: PMT status report

RD 21/03/2014

Comparison of 30 PMTs “56AVP”

Pulse height spread for

fixed LED intensity and same HV=1850V

•no stability guarantee, •few minutes averaging

8

HERSCHEL: PMT status report

RD 21/03/2014

Single Photo-electron spectra PMT 56AVP # 49667

(~1M sweeps, @2500V)

0

100

200

300

400

500

-10 0 10 20 30 40 50 60 70 80 90 100

Q, pC

LED Pedestal

9

HERSCHEL: PMT status report

RD 21/03/2014

Outcome:

• Divider production under large concern

• Stand for prototype testing ready by next week

• 56AVP could be considered as a back-up solution (more study required)

• Dividers from UA1 to be investigated (if available)

• COMPASS group from Mainz asked to search spare parts for divider housing

• LEDs worth to embed in to scintillator to be able to monitor its transparency

• The coming weeks are crucial to finalize the baseline solution for counters.