IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E 3 C 0 3

RADIATION HARD BEAM PROFILE MONITORS FOR THE
NORTH EXPERIMENTAL BEAMLINES CERN
E. Buchanan∗ , J. Cenede, S. Deschamps, W. Devachelle,A. Frassier, J. Kearney, R. G. Larsen, I. O. Ruiz
CERN, Geneva, Switzerland
Abstract
A new radiation hard profile monitor is being researchedand developed for the North Area Beamlines at CERN. Themonitor must have a spatial resolution of 1 mm or less, anactive area of 20 x 20 cm, a low material budget ( 0.3%) andbe operational in a beam that has a rate of ∼2×1011 p/s in thefull energy range of 0.5 – 450 GeV/c. The current focus is
the study of different detection mediums: silica optical fibres(Cherenkov radiation) and glass capillaries filled with liquid
scintillator. Prototypes of the different fibre candidates havebeen tested at different beam facilities at CERN: the M2
beamline and IRRAD. The key properties tested are the lightyield and radiation tolerance.

INTRODUCTION
Since the late 1970s, Multi Wire Proportional Chambers,
Delay Wire Chambers and Filament Scintillators have beenused in the North Area Beamlines to provide the profile andpositions of the beams [1]. However, the performance of
these detectors is now degrading due to aging effects andthere are limitations on the maximum intensity at which
they can operate. As part of an upgrade to the beamlines,
starting from 2027, the majority of these detectors will be replaced [2]. For the low intensity beamlines (∼ 108 particles
per spill), a scintillating fibre detector called the eXperimental Beam Profile Fibre monitor (XBPF) will be installed [3].
The XBPF consists of a single array of 192 plastic scintillating fibres (SCSF-78) from Kuraray with a square crosssection and 1 mm thickness. Each fibre is individually readout using si-pm’s. A photograph of an XBPF is shown inFig. 1. For the high intensity beamlines (∼ 1011 particles perspill), the XBPF is not expected to have sufficient radiation
tolerance, therefore a new radiation hard profile monitor iscurrently being researched and developed. Ideally the newdetector will have a similar silhouette to the XBPF, but theactive medium will be replaced with a material that has ahigher radiation tolerance. This article describes the different detection mediums that are being studied and presents
recent beam test results.

DETECTOR REQUIREMENTS
The new radiation hard profile monitor has the following
requirements:• active area of 20 cm × 20 cm,• a low as possible material budget (∼0.3% 𝑋0 ),∗ emma.buchanan@cern.ch

Figure 1: The XBPF detector.
• a spatial resolution of 1 mm,• measure particle rates from ∼ 104 to ∼ 1011 in the fullenergy range of 0.5 – 450 GeV/c,• operational up to 2 MGy, equivalent to a minimum of
8 years of operation, and• operational in vacuum (10−3 mbar) and in air.

ACTIVE MEDIUMS
Two different active materials are currently being studied:silica optical fibres and silica capillary fibres filled withliquid scintillator.

Silica Optical Fibres
Silica optical fibres are widely used in the telecommunications industry. They consist of a central silica core surrounded by a cladding layer which has a lower refractive
index, enabling the transmission of light via total internalreflection. A well-known phenomenon is the production ofCherenkov light in silica fibres when charged particles passthrough them [4]. Often for data transmission in high radiation environments, for example high energy physics experiments, this is an unwanted source of background. However,for some applications, this phenomenon can be exploited asa signal, such as Beam Loss Monitors [5].
The Cherenkov light peaks in the UV wavelengths andis emitted in a cone relative to the impinging particles direction. The angle depends on the refractive index of theWE3C03

03 Transverse Profile and Emittance Monitors

321

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E 3 C 0 3material and the velocity of the charged particle, which isexpected to be ∼ 40∘ in silica for relativistic particles [6].
Silica quartz is known to be more radiation hard comparedto plastics [7]. There are, however, two consequences of irradiation damage that will effect the performance: radiationinduced attenuation which decreases light transmission anda change in the refractive index [7].
For fibre testing, multimode optical fibre’s were purchasedfrom Thorlabs with two different diameters, 600 µm and1000 µm. These fibres where cut to 20 cm lengths using aruby fibre scribe. Additionally, quartz glass rods of 1000 µm,and length 20 cm were purchased from Hilgenberg GmbH.
These rods have no cladding and therefore have a higherrefractive index gradient with respect to air, hopefully increasing the trapping efficiency of the light.

Capillary Fibres
Capillary fibres 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. Traversing charge particles will produce scintillation
light which will then be propagated towards the end of thefibre. Liquid scintillators are intrinsically more radiation
hard than plastic scintillators. From literature, it was foundthat the light yield of liquid scintillator EJ-3091 decreases
25% per 0.5 MGy compared to a 30% decrease per 10 kGy
for plastic scintillators [3, 8]. Also from literature, liquid
scintillator BC-599-13, was found to have no change in lighttransmission up to 1 MGy [9]. Radiation damage will occur
in the quartz glass capillary but as long as the refractive
index remains lower than the liquid scintillator, light shouldstill propagate.
Two different glass capillaries were purchased fromHilgenberg GmbH, both with length 20 cm and an outer
diameter of 1000 µm. One fibre type had a inner diameterof 580 µm and the other, 800 µm. A larger inner diameter
will give a larger light yield but are more breakable. Thecapillaries were filled with liquid scintillator EJ-309 fromEljen Technology. The refractive index of the scintillator is
1.57 and the wavelength of maximum emission is 424 nm.
The liquid was contained in the fibre by gluing both ends
using NOA61 UV cure optical adhesive [10]. A photographof a liquid filled capillary is shown in Fig. 2.

Figure 2: A liquid filled capillary when exposed to UV torch.

BEAM TESTS
Different fibre tests have been performed at two different
beam facilities at CERN: The M2 beamline and IRRAD.
1 EJ309 liquid base containing 16% of the fluorescent dye DSB1

The M2 Prototype
The M2 beamline is part of the North Experimental
Area CERN. Currently the M2 beamline can provide highenergy and high-intensity hadron beams, at a momentum of
280 GeV/c and a maximum rate of 108 particles per spill.
The line can also provide muons and electrons [1]. A prototype device has been installed 69 m from the target.
A photograph of the M2 prototype is shown in Fig. 3.
The prototype is made up of three different fibre sections
with 64 fibres each of: 1000 µm optical fibres, EJ-309 filledcapillary fibres with inner diameter 580 µm, and 600 µm
silica optical fibres. They are readout individually by thesi-pms on the XBPF readout board. The prototype can berotated around the 𝑦-𝑧 axis and is mounted on a linear motor
along the 𝑦-axis. A blackbox is placed over the prototype
during operations.

Figure 3: The M2 prototype rotated at 45∘ .

IRRAD Tests
IRRAD is a proton irradiation facility at CERN. IRRAD
provides a slowly extracted primary proton beam of momentum 24 GeV/c delivered in spills with a maximum intensity of 5 × 1011 particles per spill over a duration of∼ 400 ms [11].
A quartz silica rod and a EJ-309 filled capillary (innerdiameter of 800 µm) were installed at IRRAD to test theirlight yield and light transmission while being irradiated up
to 2.85 MGy. The rod and fibre were each attached to a 30 m
1000 µm silica optical fibre (glued using NOA61), known
as a transport fibre, to transmit the light from the irradiation
area to a CMOS camera in the barracks. Two 12 V halogen
bulbs where programmed to flash in between spills of thebeam to check the light transmission. A photograph of theIRRAD setup is shown in Fig. 4. A blackbox is placed overthe setup during operations. The exposure of the camera was
set to 500 ms to ensure the full particle spill was captured
and optical filters were placed over the end of transport fibres
to stop camera saturation.

WE3C03322

03 Transverse Profile and Emittance Monitors

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E 3 C 0 3Figure 4: A quartz rod and EJ-309 capilary fibre installedat IRRAD. Two halogen bulbs are seen on the left and thetransport fibres are seen on the right (blue cladding).

RESULTS
The M2 Prototype
The M2 prototype was tested with a mixed hadron beamwith a momentum of 190 GeV/c and a rate of ∼ 3 × 105
particles per spill. A nearby scintillation paddle was used totrigger the detector and reduce noise. Example profiles areshown in Fig. 5, measured when the prototype was placed45∘ relative to the beam. Insufficient signal was measured
in the silica fibres when the prototype was perpendicular tothe beam. A higher signal was measured in the capillaries
compared to the silica optical fibres (30% compared to the1000 µm silica fibre), as expected. A 76% lower signal
was measured in the 600 µm compared to the 1000 µm. The
reduced signal when comparing the 600 µm and the 1000 µm
silica fibres is not linear, this could be accounted for by theinconsistent cutting techniques that may result in varied
light losses. A summary of the beam profile 𝜎 and average
efficiencies are shown in Table 1.
Table 1: M2 Prototype Results Summary
Fibre type

Profile 𝜎

Efficiency %1000 µm
EJ-309 Capillary
600 µm3.50 ± -0.03
3.92 ± 0.04
3.57 ± 0.01

46.4
64.8
15.1

Figure 5: Beam profile measuring using 1000 µm silica
fibres (top left), EJ-309 capillaries (top right), 600 µm silica
fibres (bottom).

Both the light transmission and light yield decrease exponentially with a 66% drop in transmission and a 95% drop inlight yield. The bulb emits a wide spectrum of wavelengths,
whereas Cherenkov light peaks in the UV. The lower lightyield may be due to increased absorption in the UV wavelengths. Increased light transmission is seen during shortperiods over the week which correlate to periods of no beam.
This increase is due to annealing. The light transmission andthe light yield for the EJ-309 capillary are shown in Figs. 9and 10 respectively. The light transmission only fluctuated
3%, suggesting a negligible difference in light transmission,
as reported in literature [9]. The light yield decreased 50%.
These results suggest that the radiation tolerance of the EJ309 capillary is higher compared to the quartz rod.

IRRAD Tests
The IRRAD setup, as shown in Fig. 4, was installed for
one week. The average rate was 5 × 1011 particles per spill
and there were limited periods of no beam. The max dose
reached was 2.85 MGy in an area of 10 × 10 mm2 . An
example image taken by the camera when the bulbs were
flashing is shown in Fig. 6. The integral of each light spot
was calculated and plotted for each spill as a function of thetimestamp for when the bulb was flashed and when the beam
was traversing. The light transmission and the light yieldfor the quartz rod are shown in Figs. 7 and 8 respectively.

Figure 6: An example image from the CMOS camera when
the bulbs are flashing. The light from the quartz rod is seenon the left and the capillary is shown on the right.
WE3C0303 Transverse Profile and Emittance Monitors

323

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E 3 C 0 3

Figure 7: Light transmission of the quartz rod.

Figure 10: Light yield of the EJ-309 capillary.
Silica optical fibres and liquid scintillator filled capillary
fibres were tested as options for a new active material replacing the scintillation fibres. From tests performed at the M2
beamline CERN and IRRAD, it was found that liquid filledcapillaries have a higher radiation tolerance, in terms of bothlight transmission and light yield compared to silica quartz
rods. This R&D effort is still ongoing. The M2 prototype
needs to be tested at higher particle rates to check that sipms do not reach saturation. Additionally, a new fibre typewill be tested: hollow core optical fibres [12] filled with ascintillation gas will be qualified later this year.

REFERENCES
Figure 8: Light yield of the quartz rod.

[1] D. Banerjee et al., “The North Experimental Area at theCERN Super Proton Synchrotron”, CERN, Geneva, Switzerland. CERN-ACC-NOTE-2021-0015, Jul. 2021.
https://cds.cern.ch/record/2774716[2] “Medium-Term Plan for the period 2023-2027 and Draft Budget of the Organization for the sixty-ninth financial year 2023”,
CERN, Geneva, Switzerland. CERN/SPC/1182/Rev., Sept.
2022. https://cds.cern.ch/record/2838413[3] I. Ortega Ruitz et al., “The XBPF, a new multipurpose scintillating fibre monitor for the measurement of secondary beams
at CERN”, Nucl. Instrum. Methods Phys. Res., Sect. A, vol.
951, p. 162996, Jan. 2020.
doi:10.1016/j.nima.2019.162996[4] S. Girard et al., “Overview of radiation induced point defects
in silica-based optical fibers”, Rev. Phys., vol. 4, 2019.
doi:10.1016/j.revip.2019.100032

Figure 9: Light transmission of the EJ-309 capillary.

CONCLUSION
The beam profile monitors currently installed in the North
Area Beamlines need to be replaced and upgraded. A scintillating fibre detector, called the XBPF will be installedin the lower intensity beamlines (∼ 108 particles per spill).
These devices do not have the required radiation tolerancefor the higher intensity beamlines (∼ 1011 particles per spill),therefore a new radiation hard profile monitor is required.

[5] S. Benítez Berrocal et al., “Beam loss localisation with an
optical beam loss monitor in the CLEAR facility at CERN”,
in Proc. 13th Int. Particle Accelerator Conf. (IPAC’22),
Bangkok, Thailand, Jun. 2022, pp. 351-354.
doi:10.18429/JACoW-IPAC2022-MOPOPT045[6] A. S. Beddar et al., “Cerevkov light generated in optical fibres
and other light pipes irradiated by electron beams”, Phys. Med.
Biol., vol. 37, p. 925, Jul. 2000.
doi:10.1088/0031-9155/37/4/007[7] V. Hagopian, “Radiation damage of quartz fibers”, Nucl. Phys.
B Proc. Suppl., vol. 78, no. 1, pp. 635-638, 1999.
doi:10.1016/S0920-5632(99)00616-7

WE3C03324

03 Transverse Profile and Emittance Monitors

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E 3 C 0 3[8] R. Ruchti et al. “Thick-wall, liquid-filled quartz capillaries for
scintillation and wavelength shifting applications”, in 38th Int.
Conf. on High Energy Physics - Poster Session (ICHEP’16),
Chicago, USA, Aug. 2016.
doi:10.22323/1.282.0935[9] M. Gui et al., “Radiation damage effects on liquid scintillatingfibers”, Radiat. Phys. Chem., vol. 41, no. 1, pp. 237-242, 1993.
doi:10.1016/0969-806X(93)90061-X[10] M. Montecchi and Q. Ingram, “Study of some optical glues
for the Compact Muon Solenoid at the large hadron colliderof CERN”, Nucl. Instrum. Methods Phys. Res., Sect. A, vol.

465, no. 2, pp. 329–345, 2001.
doi:10.1016/S0168-9002(01)00678-7[11] B. Gkotse et al., “IRRAD: The New 24 GeV/c Proton Irradiation Facility at CERN”, in Proc. 12th Int. Topical Meetingon Nuclear Applications of Accelerators (AccApp’15) Washington D.C., USA, Nov. 2015.
https://inspirehep.net/literature/1688990[12] H. Sakr et al., “Hollow core optical fibres with comparable
attenuation to silica fibres between 600 and 1100 nm”, Nat.
Commun. vol. 11, Nov. 2020.
doi:10.1038/s41467-020-19910-7

WE3C0303 Transverse Profile and Emittance Monitors

325

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3