the mu-ray project - phd_defence

INNER IMAGING OF LARGE STRUCTURES USING COSMIC

MUONS:Design, Assembly and Commissioning of a Muon Telescope

Novel Technologies for Materials, Sensors and ImagingXXVI Cycle

UNIVERSITA’ DEGLI STUDI DI NAPOLIFEDERICO II

Ph. D. Candidate :Luigi Cimmino

Tutors :Dr. Giulio SaracinoDr. Giuseppe Osteria

May 6th, 2014 - Napoli

VOLCANOS RADIOGRAPHY WITH COSMIC RAYS

muon telescope Mt. Asama (Jap.)

The muon radiography (Muography) is based on the measure of the absorption of cosmic muons in the matter.

• Muons are elementary particles with high penetrating power• A detector measures the muons direction and counts their number• By measuring the absorption factor of muons flux, we can calculate

the mean density of the rock

Eruption dynamics mostly depend on• the gas content• the composition of the magma • the conduit dimensions and shape.

Seismic,gravimetric,electromag.

methods:Several km

Muon radiography: few hundreds m

Traditional measurement methods :• gravimetric, • seismological and • electromagneticresolutions of the order of several hundred meters.

Muon radiography can improve resolutions by one order of magnitude.

MOTIVATIONS

STATE OF ART IN MUOGRAPHY• The first application was realized in 1971 by Alvarez and

collaborators for the search of unknown burial chambers in the Chephren pyramid.

• Since year 2000 Japanese researchers have applied the methodology to radiograph the mount l’Asama, the Satsuma Iwo-jima and the lava dome of mount Usu. They used both electronic detectors and nuclear emulsions.

• Emulsions allow for best resolution and don’t need power supply, but they are very sensitive to environment and can be used for short period of time. Moreover, the data reconstruction is very hard and it can not furnish real-time information

Mt.

Asa

ma

- 200

3 (J

ap.)

Mt.

Asa

ma

- 200

7 (J

ap.)

REQUIREMENTS FOR MUOGRAPHY

• Rugged and modular structure designed for easy installation and use in volcanic environment

• Large area assembly capability• Tracking of muon trajectory• High angular resolution• Fast electronics• High background rejection

• Muon’s Time of Flight (TOF)• Third plane• High planes segmentation

m

X1

Y1

X2

Y2

Third Plane

fake m from ‘albedo’

m

The measure of the Time of Flight of the muons let us

able to reject tracks coming from albedo mimicking

good trakcs

BACKGROUND REJECTION

fake m from ‘shower’m

The third plane is used to reject

events that are not aligned

BACKGROUND REJECTION

Japa

nese

det

ecto

r at

Ves

uviu

s (2

010)

• In Europe, the TOMUVOL collaboration and the DIAPHANE experiment are currently working, respectively, on muon radiography of the Puy de Dome near Clermont Ferrand and of the Grande Soufrière in Guadaloupe.

STATE OF ART IN DETECTOR FOR MUOGRAPHY

o Japanese : Scintillator bars + Photomultiplier Tubes (PMT)(6 planes, 168 channels)

o DIAPHANE : Scintillator bars with WLS Fibers + Multianode PMTs(3 planes, 96 channels, TOF capability, descend from OPERA experiment)

o TOMUVOL : Resistive Plate Chamber, gas detector(4 planes, 10k channels, descend from ATLAS experiment)

o MURAY : Scintillator bars with WLS Fibers + Silicon Photomultipliers (SiPM)

(3 planes, 384 channels, TOF implemented, brand new detector)

THE MU-RAY TELESCOPE • Formed by 3 planes

• 1 m2 sensitive area

•≈ 8 mrad angular resolution• 1 ns time resolution •Few tens of Watts power

consumption

Performance

• Plastic scintillator with triangular shape •WLS Fibers•Silicon Photomultipliers •Fast Front-end Electronics

Features

SCINTILLATORS FEATURES

Triangular plastic scintillator bars (D0-Minerva)• Robust• Fast• Cheap• Allow for spatial resolution

• When an ionizing particle hits the bar, a certain amount of light is released and must be transmitted to the photon detectors.

• WLS Fibers collect and transmit the light to the Silicon photomultipliers

• To optimize the light collection an optical glue can be used to couple the fiber with the scintillator.

Different type of transparent epoxy glues tested.

Several problems encounterd and solved:- Cracks- Bubbles- Shrinking

FIBER - SCINTILLATOR COUPLING

• Optimization of the optical coupling

• Definition of a procedure to prepare glue

Goals:

In order to thermostat photon detectors, we decided to arrange 32 Silicon photomultipliers on a single board.

We choose to design an optical connector to put forward photon detectors against fibers, so that it collects 32 fibers

OPTICAL COUPLING REQUIREMENTS

• Fiber Internal total reflection angle: 21.4°

• output angle: 35.7°• max displacement: 220mm

1,4 mm

1. Setup the Test Facility2. Organizing photo for image analysis

CONNECTOR QUALITY CHECK3.

Imag

e an

alys

is

With the software Gwyddion we measured:• Holes diameter• Alignment• Fibers placementWe have found :• All holes are aligned with statistical

error of order 0.5%• All holes are spaced within

statistical error of order 2%

Digital microscope

THE CONSTRUCTION OF THE TELESCOPE

SIPM TEMPERATURE DEPENDENCESilicon photomultipliers are sensitive to single photon, based on avalanche silicon photodiodes that works in Geiger mode and arranged in arrays of them.

The gain, and the photon detection efficiency (PDE) in single photon counting regime, is proportional to the overvoltage.

Dark counts have rates from 100 kHz up to several MHz per mm2 at 25 °C.

VBD = f(T)

G (VBias – VBD)

VBD / T ≈ 50mV/°C

0 5 10 15 20 25 30 3527.50

28.00

28.50

29.00

29.50

30.00

30.50

31.00

31.50

32.00

32.50141516131211109876

T (°C)

Vbd (V)

Voltage (V)

Current (A)

Wat

er C

hille

r

Hydraulic Heat Exchanger

CONDITIONING WITH WATER CHILLER

Copper vias improve thermal conductivity between cold plate and inner plate below SiPM

SiPM pads

HYBRID DESIGN FOR THERMAL CONDUCTIVITY

Thermal plate

Hybrid back view

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 119

20

21

22

23

24

25

26

T_dxT_sxT_cntrTA

Room TemperatureT (°C)

Current (A)

11:38 11:45 11:52 12:00 12:07 12:14 12:21 12:28 12:36 12:43 12:5018

19

20

21

22

23

24

25

T_dxT_sxT_cntrTA

Room Temperature

Time (hh:mm)

T (°C)UNIFORMITY IN SIPM CONDITIONING

Probe arrangement on the Hybrid board (bottom view) and is disposition inside the polystyrene’s brick insulator (top view hidden).The top is coupled with the aluminium passive cooling system through a wafer made of conductive gum and a copper’s buffer . Three Peltier Cells was emploied

during the experiment each one located respectively at ¼, ½ and ¾ of the lenght L of the cooper buffer. We arranged a serie circuit with the cells.

T_sx • •

T_cntr T_dx

T_ms T_md

H

TEST TO CHECK HYBRID TEMPERATURE UNIFORMITY

0.0 0.5 1.0 1.5 2.0 2.50.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0TENVIRONMENT - TEXP (°C)

Electric power (W)

PELTIER BASED CONDITIONING SYSTEM

• Based on Peltier cells • Reduction of power consumption• Designed to minimize internal

temperature variations due to external changes

• Dedicated control for each PCB• Sets temperature condition for all

housed SiPMs at the same time • Works with passive cooling• Could be supplied by solar cells

system

FRONT-END ELECTRONICS Low power consumption

Application-Specific Integrated Circuit SPIROC

Each slave board is programmed and read by the FPGA controller assembled on the master board

12 slave boards are controlled by a single master board

Data flows are managed by a PIC micro controller that links the telescope electronics to the PC through an USB connection

A monitoring board reads each couple of PT1000 thermosensors mounted on the SiPMs board

Room conditions are constantly monitored with a thermo-hygrometer connected to the PC

PCSlow

Control

Master Board

Slave Board

32 x SiPMs

Slave Board

32 x SiPMs

Slave Board

32 x SiPMs

…

…

Raspberry Pi

Data Base (MySQL)

Sensors

Raw data storage

Data

Power Supplies

Environment

DATA ACQUISITION AND REMOTE CONTROL

Master Board

Read Voltages

Setup Voltages Applying

Settings

Data Analysis

Remote Alarm Website

USE OF THE DATABASE AND RAW DATA

computerLinux OS DB

Data Quality

ONLINE

OFFLINE

COMMISSIONING OF THE TELESCOPE• Study of accidental coincidences• 95% trigger efficiency per plane including acceptance• Good correspondence between the angular distibution of muons (black in

the chart) and the expected one (red)• Precise calibration and working point determination

Zenit angle (rad)

CAMPAIGN AT THE VESUVIUS

MURAY AUTOMATIC REMOTE SYSTEM• Improvement of remote control software (automatic mail delivery

service in case of warnings and errors)• Realization of an automated system for the telescope operations• Test of Voltage Follower Data Acquisition without the chiller

1. The PC is a Raspberry Pi minicomputer(few watts consumption)

2. SiPMs temperature is controlled using Arduino boards(10 bits DAC – 0.15°C sensibility)

3. Power supplies are controlled remotely(no handling required)

ELECTRONICS UPGRADE • PIC Board has been replaced by a pin-to-pin connection with the Raspberry Pi GPIO

• Allow for an interrupt based protocol

• Low level management of the communication

• Increase of the data transmission bandwidth

• Reduction of the dead times

• Each slave board has a Switching Power Supply

BEFORE

AFTERPC

PIC Microcontroller

MASTER Board

Raspberry PI

Mu-Ray from June to December 2013in collaboration with TOMUVOL to compare techniques.

CAMPAIGN AT THE PUY DE DOME (FR)

ROCK THICKNESS COMPARISON

Vesuvio (Ita) – 1.281 m

Puy de Dome (Fr) – 1.464 m

< 500 m

> 1500 m

Region of interest

HOW TO MEASURE THE TOF?

m

tX1

tY1

tX2

tY2

• Muons cross the detector• A certain trigger logic is

satisfied• Relative time are recorded

TOP Plane DOWN Plane

TIME EXPANSION

• A local trigger is produce on the slave board and transmitted to the master when a particle hits the relative plane

• Master board receives all local triggers and if they fulfill the trigger logic, it sends to all slaves a global trigger (stop)

• We want to measure the time between every single local trigger and the stop signal

• From the production of the local trigger to the stop signal a capacitor is charged on each slave boards

Local trigger Local trigger

Enable window

Stop Stop

Char

ge

Discharge

EXPERIMENTAL MEASURE OF THE TOF

Measured TDC spread

1.6 counts

320 ps

• Linear response• RMS indipendent from the

delay

delay (ns)

counts (a.u.)

coun

ts (a

.u.)

MONTE CARLO EXPECTED TOF (2 X-VIEW TRIGGER)

Horizontal tracks

mean sigmaPeak 1 400.2 3.13Peak 2 417.2 5.71 Peak 1 400.2 3.1Peak 2 417.2 5.42

TOF 3.4 nsTOF 3.4 ns

TOFexp = 1.03 m/c = 3.43 ns

Transverse tracks

TOFexp = 1.41 m/c = 4.70 ns

mean sigmaPeak 1 408.6 5.46Peak 2 455.4 5.81 Peak 400.2 3.03

Tmeas C.FibraTOF 1.68 6.4 4.72 nsTOF 11.04 6.4 4.64 ns

(0.96 m)

CONCLUSIONS

• The construction of the MU-Ray detector started in the spring of 2011

• Tests and experiments to find best materials, sensors, computing and monitoring solutions lead to the development of a remotely controlled muon detector

• Its precise calibration and characterization allowed to set for best performance

• In April 2013 we “see” the Vesuvius, in the first outdoor employment

• From June 2013 to December 2013 the telescope has operated at the Puy de Dome

• Data analysis is in progress

• Improvements and new features are in progress

Thanks

mail :: [email protected]

SPARE SLIDES

The special tool in the picture was designed by technical support to fix fibers to the connector. In such way, side by side, fibers lower profiles fits naturally under effect of gravity, so once all fibers are inserted in the relative guides to the connector, they are glued to it with high precision.

Arbitrary Unit

On the right, we can see a well positioned fiber that comes outside the hole. Thank to such analysis we were able to improve the fiber positioning tool, to dispose all 32 fiber inside the connector using a precision mechanics that softly align the fibers at same level outside the holes.

FIBERS PLACEMENT

Arbitrary Unit

Incorrect fiber placement

Well placed fiber

TRIGGER EFFICIENCY IN 6 PLANES CONFIGURATION

• The trigger efficiency has been measured setting up six different 5 planes trigger configuration

• With a counter we measure the number of coincidences in a fixed time window • The trigger efficiency for each configuration is the ratio between the rate measured in 6

planes configuration and the rate of a given 5 planes configuration

DETERMINAZIONE DEL FATTORE DI ASSORBIMENTO

Only PdD trackAll golden tracks:Calibration + PdD

PdD trackscontribution.

Calibration

Calibration

Total number: 11.4 Milion

<Golden track rate * dead time> = 2.0 Hz

∑ Ntk xyT DAQ

×DTF Corrected for the deadtime

Number of days pointing the PdD = 92.Due to pedestals and counting measures made between to different runs the effective DAQ duration is : 6.89*106 s ≈ 79.74 days

<Golden track rate * dead time> = 2.0 Hz<Golden track rate > = 1.6 HzEffective time = 6.89*106 sNumber of expected tracks = 1.6 * 6.89*106 = 11.02 MilionNumber of integrated golden tracks = 11.4 Milion

MUON RADIOGRAPHY SCHEMA• We generate in projective geometry a map of the absorption of the flux of muons through

the edifice

• The comparison between the experimental absorption and theoretical data allows to estimate the mean density of the rock

• Theoretical data are rappresented by the expected muon fluxes function of the rock thickness (in km water equivalent), at different zenith angles.

G-APD•Sono matrici di APD collegati in

parallelo

•Per la rivelazione di luce verde si preferisce usare n su p-substrate

-

•In regime di Single-photon counting si ha che il guadagno è proporzionale al numero di fotoni incidenti

LA MODALITA’ GEIGER

•La moltiplicazione di portatori liberi avviene sia coinvolgendo le lacune, che con un aumento esponenziale dei portatori di carica

•Il funzionamento di ogni singola cella è ripristinato mediante il meccanismo di quenching

APD Modes (lineare)

G-APD Mode (esponenziale)

IL DARK NOISE• L’overvoltage, la differenza tra la

tensione di bias e quella di breakdown, ha effetto sui conteggi di buio, attraverso la tensione di breakdown. Il guadagno A, e di conseguenza l’efficienza di fotorivelazione (PDE), è proporzionale all’overvoltage e siccome una variaizone in temperatura produce cambiamenti nella tensione di breakdown di circa 50 mV/°C, la PDE varia di qualche punto percentuale a grado Celsius. I conteggi di buio (dark counts) sono prodotti a partire da cariche libere generate per aggitazione termica con una frequenza compresa tra 100 kHz e 10 MHz per mm2 at 25 °C.

• Si noti che variazioni di 8°C producono un aumento o una diminuzione, a seconda che si tratti di un incremento in temperatura o meno, di un fattore 2 dei dark counts.

The Peltier Cell

We have dealt with Peltier cells manifactured by Global Component Sourcing with specifications, as it follows from the related datasheet

Ora, rispetto alla capacità del calore flussare lungo le le tre direzioni di un solido, se si considerano due parallelepipedi di rame di uguale lunghezza e larghezza ma con spessori differenti, il flusso calorifico risulta avvantaggiato quando attraversa ortogonsaalmente lo spessore minore, ma di converso è sfavorito il passaggio lungo il piano che presenta una superfice ridotta rispetto a quella di spessore maggiore.

mmm

mmm

𝜑𝑜𝑟𝑡

𝜑𝑝𝑙𝑎𝑛

1

2

𝜑𝑝𝑙𝑎𝑛1=−18×10×10−9

200×10−3𝑘𝑐𝑜𝑝𝑝𝑒𝑟∆𝑇𝜑𝑝𝑙𝑎𝑛 2

=− 18×3×10− 6

200×10−3𝑘𝑐𝑜𝑝𝑝𝑒𝑟 ∆𝑇 𝜑𝑝𝑙𝑎𝑛 2

=300𝜑𝑝𝑙𝑎𝑛1

Thermal conductance Peltier Cell

DIRECT GPIO CONNECTION

Protocol main features:

• RPi set in RUN mode the master so that acquisition starts

• In the case of a trigger, the RPi stops data acquisition and sets the master in DIAG mode. The master reads every slave and sends the FIFO_READY to RPi.

• The trigger and the FIFO_READY signals are managed by the RPi as hardware interrupts

• The RPi reads master memory sending 32 clock pulse per time and receiving 32 bits of data. Once the FIFO is empty the master reset FIFO_READY and waits for RUN mode

• At the end of every operation the receiver responds with the acknowledgement signal

HOW TO MEASURE TOF?

m

tX1

tY1

tX2

tY2

• Muons cross the detector• A certain trigger logic is

satisfied• Relative time are recorder

TOP Plane (A) DOWN

Plane (B)

Toy Montecarlo Spreads generationo Physics : 700 pso TDC : 600 ps

ProblemNo information about who

triggers

MODEL OF TIME OF FLIGHT

• We use a trigger logic that takes into account only the X-view (2 boards)

• In the Toy Montecarlo we will consider all expansion factors having the same value E

Expected Distribution

DISTRIBUTIONS SHAPE CHECK

4 PTL

2 PTL

• Due to the variability of the trigger board in 4PTL configuration, distributions present different behaviors which are not easy to be separated

• In each distribution, the first peak is about trigger events (mean value off = 400, standard deviation = 3.4)

MODEL EXPECTATION CHECK (HORIZ. MUONS)

2 PTL4 PTL

MODEL EXPECTATION CHECK (TRANSV. MUONS)

2 PTL4 PTL

HORIZONTAL TRACKS TOF COMPARISON

2 PTL4 PTL





TOFexp = 1.03 m/c = 3.43 ns

TRANSVERSAL TRACKS TOF COMPARISON

2 PTL4 PTL

TOFexp = 1.41 m/c = 4.70 ns





(0.96 m)

(1.01 m)

CONCLUSIONS

• We shown how to calculate the time of flight of muons when the flux is bidirectional and only relative time information are available

• A toy montecarlo has been developed to recreate a simplified muons detector

• We develop a model to analyze data distributions and calculate the time of flight of muons

• Comparing two different trigger configuration we have verified the 2 plane trigger model

• Design of the Telescope• Optimization of the light efficiency fiber - scintillator coupling• Fibers connector

• Construction of the Telescope• Assembly supervisor• Tools realization

• Study on thermal stabilization of the Telescope• Design of an hydraulic circuit to use with industrial water chiller• Realization of a Peltier cells based cooling prototype

• Detector Commissioning• Trigger Efficiency

• Realization of an automated remote control system for slow control and data taking

• Measurement Campaigns at Vesuvius and Puy de Dome• Improvement and characterization of a second generation

electronic system

• Study of the TOF problem and Realization of a model suitable for the Mu-Ray detector

SUMMARY OF MY MAIN CONTRIBUTIONS

the mu-ray project - phd_defence

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