Radiation Hard Beam Profile Monitors for theNorth Experimental Beamlines CERN
E. Buchanan, J. Cenede, S. Deschamps, W. Devachelle, A. Frassier, J. Kearney,
R. G. Larsen & I. O. Ruiz
IBIC 2023
Saskatoon Canada

The North Experimental Area CERN
H2H4H6H8

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Testbeam Areas& Experiments

K12 - NA62
M2 - COMPASS/AMBER●●●The North Experimental Area started operation in 1978
It is the largest experimental area at CERN
It has 6 beamlines totalling 5.8 km

https://cds.cern.ch/record/2774716/files/CERN-ACC-NOTE-2021-0015-NA.pdf

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Intensity 103 - 1010 (future upgrades to 1011)
Momentum 1 - 450 GeV/c
Muons, electron, protons, mixed hadrons and heavy ions
Secondary beams, slowly extracted (unbunched) over 4.8s or 9.6 s

Emma Buchanan

2Beam Instrumentation in the North Experimental Area
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There are different devices that measure the beam profile and intensity○ Scintillator paddles○ Multi-Wire Proportional Chambers (MWPC)○ Delay Wire Chambers (DWC)○ Filament Scintillators (FISC)
Many of them are as old as the North AreaExpertise is lost and they are difficult to maintain
It’s time to upgrade!

Detector descriptions given on page 27 of the pdf: https://jinst.sissa.it/jinst/theses/2018_JINST_TH_001.pdf

Emma Buchanan

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XBPF Scintillator Fibre Detector●The XBPF is a scintillating fibre detector●

It was designed as a profile monitor for the East Experimental Area CERN●

It is readout using si-pms●

Suitable replacement profile monitor for the H2, H4, H6 & H8●

It is not suitable for the higher intensity lines K12 and M2○Scintillating fibres don’t have sufficient radiation hardness

Emma Buchanan

4New Radiation Hard Profile Monitor Requirements●

Active area of 20 cm x 20 cm●

A low as possible material budget 0.3% X0●

A spatial resolution of 1 mm●

Measure particle rates from ~104 to ~1011 in the full energy range of 0.5 – 450 GeV/c●

Operational up to 2 MGy, equivalent to a minimum of 8 years of operation●

Operational in vacuum (10-3 mbar) and in air

Emma Buchanan

5Initial Design Concepts●

Design a detector that has a similar silhouette to the XBPF

○Easier for integration in the beamlines■ Shared vacuum tank and motorisation designs○●●

Reuse the XBPF si-pm readout board if possible

A more radiation hard detection medium is needed○

Silica optical fibres○

Hollow core fibres○

Capillary fibres

Investigate alternative photodetectors

New XBPF motorisation design
Emma Buchanan

6Fibre Options

Traditional Silica Optical Fibres●

Silica Fibres propagate light via total internal reflection●

A well known phenomenon is the production of Cherenkov light in silica fibres whencharged particles pass through●●○Often at CERN this is a unwanted source of background○

For this application maybe it can be the signal

Pros:○Fibres are cheap and are available in a variety of diameters○

Silica glass known to be more radiation tolerant than plastics

Cons:

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Chrekenov signal is smaller than a scintillation signal○

Light is produced at an angle, may need to tilt detector relative to beamline■ Complicates the installation
https://iopscience.iop.org/article/10.1088/0031-9155/37/4/007/pdf

Emma Buchanan8

Capillary Fibres●Capillaries are small tubes of quartz glass with a hollow core●

They propagate light via total internal reflection if you fill them with a material
with a higher refractive index than glass●

One option is to fill them with liquid scintillator

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Pros:

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Liquid scintillator should have a higher radiation tolerance than solid
scintillators○

The glass might discolor with radiation damage but only needs tomaintain a lower refractive index than the liquid scintillator○

Both materials are relatively cheap and capillaries come in a variety ofsizes

Cons:

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They are difficult to fill and are very fragile○Liquid scintillator is a “dangerous” material
Emma Buchanan

9Beam Tests

M2 Beamline North Area CERN

M2 Prototype
Silica Optical Fibre 600 μm

Silica Optical Fibre 1000 μm

EJ-309 Filled Capillaries

XBPF SiPM Readout Board

Fibre Layout
Emma Buchanan

12M2 Prototype Installation and Beam Conditions●y-z rotation

First installed in April 2023:○ Rate was ~3x105 particles per spill○ 190 GeV hadrons
Emma BuchananLinear motor along x-axis

13Preliminary Results●Prototype was tilted 45° relative to beam due to insufficient signal in silica fibres at 0°●

Example profiles for single particle spills●

Higher signal measured in the capillaries compared to silica fibres●

Higher signal measured in the 1000 μm silica fibres compared to 600 μm silica fibres

Beam Halo

Emma Buchanan

14Preliminary Results●

Prototype was tilted 45° relative to beam due to insufficient signal in silica fibres at 0°

Fibre Type

Profile σ

Efficiency %1000 µm3.50 ± 0.03

46.4

EJ-309Capillary

3.92 ± 0.04

64.8

600 µm3.57 ± 0.01

15.1

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Wider beam profile measured in the capillaries compared to silica fibres○ Mostly likely due to cross talk●Efficiency higher in capillaries as expected due to higher light yeilds

Emma Buchanan15

M2 Prototype - Quartz Rods●

Preliminary Results at 45°

600 μm silica fibres replaced by 1 mm quartz rods●

For the second installation in August
2023, we replaced the 600 μm silica
fibres with 1000 μm quartz glass rods●

Removing the cladding and jacket
increases the refractive index
gradient●

Hopefully increasing light yield andtrapping efficiency

Silica Quartz
Rods 1000 μm●●●Quartz Silica Rods

●Emma Buchanan

EJ-309 FilledCapillaries

Silica OpticalFibre 1000 μm

Rate was ~8x106 particles per spill
Large Muon BeamQuartz rods have slight higher signal
compared to 1000 μm silica fibres
Analysis ongoing
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IRRAD

IRRAD Setup
IRRAD Beamline

IRRAD Barracks

2 Halogen Bulbs

2 x 30 m Transport Fibres

Fibre Support

Capillary Fibre & Silica Quartz Rod

CMOS Camera

Black Box
A black box is placed over the setup in the beamline
Emma Buchanan

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CMOS Camera Readout in the Barracks●Two images are taken:○Before the beam arrives the bulbs are flashed○

When there is beam●This allows us to measure the light transmission and thelight yield●

The variable plotted is the integral of the individual fibre spots●

Optical filters on both fibres to avoid saturation

Example when bulb is flashed

Emma Buchanan

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IRRAD Beam Conditions●

IRRAD is a proton irradiation facility at CERN●

Proton beam of momentum 24 GeV/c●maximum intensity ~5x1011 particles per spill●Spill length of ~400 ms●

We installed at IRRAD for 1 week in August 2023

●Total dose was 2.85 MGy over an area of 10x10 mm2●Only a few periods of no beam

Emma Buchanan

20Preliminary Results - Quartz Rod Results
63% decrease

94% decrease●

Larger decrease in light yield compared to light transmission●

Bulb has wide range of wavelengths compared to the UV Cherenkov photons●

Periods of annealing when there is no beam
Emma Buchanan21Preliminary Results - EJ-309 Capillary Results
3% variation

49% decrease●

Decrease in light yield but negligible change in light transmission●

Comparable to results we have seen in literature

https://www.sciencedirect.com/science/article/abs/pii/0969806X9390061X#!

https://pos.sissa.it/282/935/

Emma Buchanan

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Future Plans&Conclusions

Future Plans●

Reinstall the M2 prototype to check for saturation at higher beam intensities●

Test hollow core fibres filled with scintillation gases●

Continued collaboration with colleagues working on FLASH therapy applications○

FLASH radiotherapy will use very high energy electrons (VHEE) in
milliseconds to treat cancers○

At the moment, there is no clear candidate for a beam profile monitor○

One of our fibre candidates may be suitable■ Monitor must be able to measure charges from 10pC to 40nC
CMOS Camera■ Spatial resolution <1 mm○Quartz Fibre Array

Currently tested silica optical fibre and quartz rods

A Novel Fibre Optic Monitor for VHEE UHDR Beam Monitoring: First Tests at CLEAR (ipac23.org)

Emma Buchanan

24Conclusions●An R&D effort is ongoing to find a radiation hard active medium, based on fibre optics, that would be suitable for a newradiation hard beam profile monitor●Silica Optical fibres, quartz rods and EJ-309 capillaries have been tested in the M2 beam line up to x106 particles per spill○ Capillaries have the highest light yield○ Silica fibres and quartz rods are required to be tilted to 45 degrees for signal to be seen
○ Higher intensity beams are needed to check that saturation is not reached●

A EJ-309 capillary fibre and silica quartz rod were tested at IRRAD up 2.85 MGy○ The capillary was found to have a larger light yield and greater radiation tolerance than the silica quartz rod●Hollow core fibres filled with a scintillation gas will be tested later this year

●In parallel, the fibre candidates are being tested for their use in FLASH therapy applications○ Results of these tests will be presented at the FLASH Radiotherapy and Particle Therapy (FRPT) Conference inToronto in December 2023

Emma Buchanan25

Thank You
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