The Optical Scattering Calibration System at SNO+ KRISH MAJUMDAR IOP 2015
Contents Introduction SNO+ Why and how to monitor optical scattering Hardware Overview Laser Heads and Laser Head Control Laser Head Monitoring Optical Fibres Fibre Switch and On-Detector Components Commissioning and Current Status Future Plans 30 March 2015 2
Why Monitor Optical Scattering? SNO+ [Sudbury Neutrino Observatory] Scintillator-based neutrino detector Broad physics program Neutrinoless Double Beta decay Solar neutrinos Supernovae neutrinos Geo-neutrinos Reactor neutrinos Need to understand detector response Geometry (reflections, refractions) Materials (absorption, re-emission, scattering) All wavelength-dependent 30 March 2015 3
How to Monitor Optical Scattering? Use known light sources Known wavelengths, intensities, directions ELLIE : Embedded LED Light Injection Entity System of LEDs + laser heads, optical fibres Multiple positions on PSUP Avoid contamination of detector material Can illuminate multiple regions of detector SMELLIE : Scattering Module of ELLIE Light from laser heads sent into detector Isolate PMTs hit by scattered light Reconstruct scattering position Determine scattering angle distribution 30 March 2015 4
Hardware : Overview MASTER mode SMELLIE controls SNO+ triggering SLAVE mode SNO+ controls SMELLIE triggering 30 March 2015 5
Hardware : Laser Heads 4 Laser Heads Pulsed-diode, manufactured by PicoQuant 375nm, 407nm, 446nm, 495nm 10kHz repetition rate (limited by internal SMELLIE electronics) Very short pulses < 100ps FWHM Laser heads better suited than LEDs Shorter pulses Narrower wavelength distribution Coherent light higher intensities + better collimation Better coupling into fibres with small numerical aperture Less dispersive broadening pulse stays short in detector 30 March 2015 6
Hardware : Laser Heads 30 March 2015 7
Hardware : Laser Head Control SEPIA II Laser Driver Unit Manufactured by PicoQuant Computer-controlled by user: Repetition rate Intensity Only drives a single laser head at a time Laser Switch Designed and manufactured at Oxford 1 input channel (from SEPIA) 5 output channels (4 laser heads + 1 spare) Mechanical relays route control signals to desired laser head Computer-controlled by user: Laser head by wavelength 30 March 2015 8
Hardware : Laser Head Control 30 March 2015 9
Hardware : Laser Head Monitoring Per-pulse energy (intensity) variation Few percent @ high intensity Larger variation @ low intensity Measure per-pulse intensity before detector Monitoring PMT Unit Designed + manufactured at Oxford Receives fraction of laser head output (via beamsplitter) Convert to measureable PMT pulse Samples and stores pulse s maximum voltage Peak height related to laser head intensity Output to CAEN ADC for real-time DAQ, viewing and later offline analysis Voltage on CAEN independent of waveforms from rest of detector 30 March 2015 10
Hardware : Laser Head Monitoring PMT pulse : 700ns wide Peak sampling : 200ns after pulse start 30 March 2015 11
Hardware : Optical Fibres Corning Infinicor SXi Multimode 50µm diameter graded index quartz core Optimal wavelength range : 750 1450nm SMELLIE wavelengths outside optimal range 12 detector fibres : 50m length 0.5dB attenuation per fibre Low radioactivity 0.2647g total of 238 U, 235 U, 232 Th, 40 K in 12 fibres > 1.8876g total in 9438 PMTs 30 March 2015 12
Hardware : Fibre Switch Optical Fibre Switch Custom-design, manufactured by Laser Components UK 5 inputs (1 per laser head, 1 spare) 14 outputs (1 per detector fibre, 2 spare) Micro-Opto-Electromechanical systems and internal switching blocks create unbroken path between desired input and output Computer-controlled by user: Input (laser head by wavelength) Output (detector fibre by ID) Some attenuation through Fibre Switch 0.5 2.5dB depending on exact choice of input + output, wavelength 30 March 2015 13
Hardware : On-Detector Components Detector fibres capped by collimators Designed + manufactured at Oxford 3 half-opening angle Illuminate several PMTs in beam-line 4 locations (mounting plates) on PSUP 3 fibres per plate Each fibre at different angle to detectorcentre (0, 10, 20 ) Allows different PMTs to be illuminated Different distances travelled in different materials Designed + manufactured at Oxford Delrin Does not warp under prolonged contact with water Low radioactivity : 0.001914g total of 238 U, 235 U, 232 Th, 40 K in 4 plates 30 March 2015 14
Commissioning and Current Status March 2014 : Off-detector completely installed and tested at SNO+ On-detector 6 of 12 detector fibres installed Remaining fibres to be installed later in 2015 Integration into other SNO+ systems ongoing Data taken during AIR fill phase Tune SMELLIE MC simulation Correct simulation fibre positions and directions to match data 11 half-opening angle beams fit data better discrepancy not yet understood 30 March 2015 15
Run 7136 (Air Fill) - Fibre FS237-495nm : view of forward beam location 30 March 2015 16
Commissioning and Current Status December 2014 : Remote operating systems completed and tested Data taken during PARTIAL WATER fill phase Significantly different optics Total internal reflection from water surface No clear forward beam Difficult to analyse MC simulation of geometry incomplete 30 March 2015 17
Run 8944 (Partial Water Fill) - Fibre FS237-495nm : view of forward beam location 30 March 2015 18
Future Plans 5 th laser Supercontinuum (continuous wavelength distribution) Can choose wavelengths in 130 Te low-absorption regions Currently being tested at Oxford Further data needed Full water fill later in 2015 All fibres and laserhead combinations Laser intensity vs. Monitoring PMT output vs. Number of triggered PMTs 30 March 2015 19
Thank You Also see: Measurement of the Rayleigh Scattering Length at SNO+ Stefanie Langrock 31 st March - PPAP Parallel: Neutrino Detectors II @ 4.15pm Questions? 30 March 2015 20
Backups and Extras 30 March 2015 21
Laserhead Wavelength Profiles 30 March 2015 22
Laserhead Time Profiles 30 March 2015 23
Fibre Switch Internal Design 30 March 2015 24
Collimator Design Quartz rod Glass Ferrule Strain Relief Tube (stainless steel) Fibre Placement Tube Glue Fibre Protection Jacket 30 March 2015 25
Run 7136 (Air Fill) - Fibre FS237-495nm : view of back-reflection location 30 March 2015 26
Run 8944 (Partial Water Fill) - Fibre FS237-495nm : view of back-reflection location 30 March 2015 27