Optical Calibration Updates Presentation for SK-UK Meeting 2016 Neil McCauley, Lauren Anthony, Adrian Pritchard, Joachim Rose 1

Calibration Allows us to calibrate and monitor the photodetectors, their response and the detector medium properties. Reduce both errors in photodetector calibration and the uncertainties in the reconstruction of the neutrino events. Injects light pulses of known emission time and intensity. Location, direction and profile of the light pulses will also be known. Light injections in several visible wavelengths using LEDs as the light source. 2

So far Stability measurements Investigating source of instability Monitoring LED temperature Have a student working on using FPGA to produce pulses 3

4 Pulser board LED Anode MOSFET Cathode MOSFET LED coupler Fibres

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6 Test stand 495nm LED is currently coupled to 3 optical fibres One to a photomultiplier tube One to an optical power meter with pW sensitivity One spare Pulse generator controls pulses delivered to the board Future iterations will control pulses with FPGA board, allowing more flexibility, simpler design, reduced cost Anode and cathode voltages controlled through power supplies Oscilloscope to measure rise/fall time and pulse width of PMT pulse

Send anode pulse at time t 1, forward current through LED, photons are emitted. Send cathode pulse at time t 2, this sends reverse current through LED. Charges swept out of depletion region and LED turned off. Pulse width controlled by anode/cathode voltages. Pulse control Relative delay t1t1 t2t2 7

Pulse stability We know that there are a number of instabilities Pulse to pulse stability generally within ~2% Observed some drift in photon number when taking data over long periods of time. Possible causes: Temperature instability LED (notoriously temperature dependent) PMT Power meter Is the pulse generator not accurate enough for our purpose Other Real time pulse monitoring will be vitally important. Understanding each pulse fully will allow proper calibration. 8

9 Pulse stability 3 measurements at same delay 1 measurement at constant delay We find a good level of stability pulse to pulse overall. Some drift in the photons per pulse at constant relative delay We see some instability when using the same delay when measurements are taken after the equipment has been restarted.

Approximating pulse shape as Gaussian with different σ for left and right side We can calculate average pulse charge using 3 factors; rise time, fall time, peak pulse height Top plot is average photons over time, bottom is approximate pulse charge over time Behaviour is very similar, indicating variations are in source rather than measurement

Plots here are Fractional charge error vs LED on time. Charge uncertainty calculated in best (top) and worst (bottom) case scenario, as correlations unknown Gives upper limit on pulse to pulse fluctuations

Temperature sensor Part of stability measurements Using Arduino to control MPC9080 sensor chip Seen fluctuations in photon count Is this the LED? Potentially use Arduino to Drive Peltier cooler and regulate temp 12

Hardware development 13 Stage 1. Sandwiched LED between sheets of Cu and thermal padding. Used original LED coupler. Applied Peltier cooler and heat sink. Stage 2. Compact and more robust design. LED contained inside. Able to secure board/fibre coupler to pulser board/LED coupler without permanently attaching.

Current system 14 Above is the current setup with an Arduino controlled temperature sensor. (Other 2 boards are DAC and ADC which are not in use for this test). Connection is via USB to Mac. Temperature sensor has now been removed from the breadboard and has been attached to the coupler itself. This make is easier to get the remp sensor inside the metal box containing the pulser board. It is attached to the breadboard via a cable. USB connection is the same.

Pulser board Newer, more robust coupler attached to current board. Adafruit temperature sensor attached to coupler. Capton tape stops the Cu block from shorting circuit. Cu is attached to this with epoxy. 15

Pulser board 16 Temperature sensor is connected to an Arduino board outside metal box via the grey cable. One python script controls both the temperature and stability measurements.

Temperature measurements Plot of photon v time and temp v time. What seen 17

Water Tank Located in basement Some work still needs to be done to prepare for measurements. Water will be treated using chlorine. Tank will be painted and lined with fabric. 18

Current Status Tank set up in basement Will have two test stands set to take measurements One in lab One in tank in basement Becoming familiar with WCSim 19

Future plans T2K-SK analysis for Nue Pi0? Optical calibration in SK Preparing tank for measurements Potting PMT Painting and lining tank Inserting fibres Undertaking shifts at SK in April 20