The Pierre-Auger PMT Test Stand Chris Jillings Feb 6, 2002

Lest anyone think these are all my ideas… Thanks to –Professor Arisaka –Arun Tripathi –Jonathon Kubic –Tohru Ohnuki –Professor Hauser –Several others

Pierre-Auger A cosmic-ray observatory Primaries with E>10**20 eV Calorimetric tanks in Argentine pampas

Concept of Auger Hybrid Detector Fluorescence Detector Surface Detector (Water Tank) PMTs

Tanks Shower particles hit tanks Emit Cherenkov light in water Cherenkov light detected by three PMTs

PMTs Photonis XP1805 PMTs

Expected range of PMT signals Need to observe single muons for calibration. Also need to be able to observe showers with energy up to eV. Based on simulations, we need to be able to observe from 50 to 50,000 pe/25 ns. –Linearity over a large range of anode currents required.

Auger Electronics Huge Dynamic range –15 bits LSB = signal from 1 photoelectron PMT must be linear

Auger PMT requirements Good quantum efficiency in nm range. Standard operating gain of 2x10 5 (to match the FADC dynamic range to expected signals). Good linearity up to 50 mA anode current (corresponding to the largest expected signal). Dark pulse rate < 10 KHz. Afterpulse ratio < 5% (200ns-5000ns from main pulse). Rise time < 10 ns. Transit time spread < 10 ns.

Linearity If the input light is doubled, is the output doubled? (Integral non-linearity) Have two LEDs –Pulse LED A –Pulse LED B –Pulse Both Is the whole the sum of the parts?

Linearity (contd.) Two pulsed blue LEDs run like, A, B, (A+B), A, B, (A+B) …… Non-Linearity is given by deviation of (AB) from sum of A and B.

Why this is a good idea Do not need calibration of electronics. Do not need calibration of light source. Do not need to compare against a reference.

An example

Why this is hard The two LEDs must have no cross-talk If pulsing LED A affects LED B then the system is will not work because the light from A&B together is different than A+B. Grounding

Fast LED Pulser nF 110 TTL 5 nF TTL

LED Control Comp I/O card Comedi Ref V (A) Ref V (B) A B Trigger

Digital Control Trigger goes to A, B and read-out. Trigger and A go to AND gate. If A high, trigger passes and LED A pulses. Ditto B. If both A and B low, no light but electronics still triggered: pedestal

Analog Control Want high impedance. Use non-inverting amp. + - R1 R2 G = 1+R1/R2 If G is small, will oscillate! Use a Slow op amp: a 741!

Part II Testing 16 PMTs at once

Linearity Test (again) Dynamic range: to read out on ADC want only 10% of PMT signal But we need all of PMT signal for other measurements! A signal splitter.

The Splitter If I could change one thing, it would be the splitter To 50  loads R in = 50 

The Splitter LeCroy QDC 50

LeCroy QDC Inputs Are active They are not: 50

The Splitter LeCroy QDC 50 Buffer

How I would do it next time R R R Buffer Atten

PMT HV control DC-DC HV –12 V power –Control ref 0-2.5V Use 32-chan analog output card for computer-control of HV. UEI ( Runs under Linux

What worked All the DC stuff Commercial PCI cards (mostly) The light sources

What worked with effort Splitting HV control with LeCroy 1440

A Proposal Get a good scope with built-in math Make sure the scope talks ethernet or gpib Run the system under LabView Use a relay-switch MUX to look at PMTs in turn.