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12th Int. Beam Instrum. Conf.
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IBIC2023, Saskatoon, Canada
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SYNCHROTRON LIGHT MONITOR FOR THE ADVANCED
PHOTON SOURCE BOOSTER SYNCHROTRON∗
K. P. Wootton† , W. J. Berg, W. P. Burns III, J. R. Calvey, J. C. Dooling, L. Erwin, A. H. Lumpkin,
N. S. Sereno, S. Shoaf, S. G. Wang, Argonne National Laboratory, Lemont, IL, USA
Abstract
A new synchrotron light monitor has been tested for thebooster synchrotron of the Advanced Photon Source. Visible
light synchrotron radiation is collected by a mirror on a pathtangential to the electron beam orbit, and directed to an
optical imaging system and camera. This is planned to be a
non-intercepting, transverse beam-size monitor even withthe higher stored beam charges (∼17 nC) needed for theAdvanced Photon Source Upgrade. In the present work,
we describe the present synchrotron radiation diagnostic
layout. An analysis of the synchrotron radiation power on
the mirror, the optical layout with components, and featuresof the control system will be presented.

INTRODUCTION
Synchrotron radiation (SR) presents a significant thermalload on components in electron storage rings. As such, typically absorbers are designed with an inclined profile, andcomposed of a metallic material such as copper, to conduct
heat away from the surface.
The motivation for the present work is to enable accurate
measurement of beam properties during high-charge studiesof the booster synchrotron for the Advanced Photon Source
Upgrade (APS-U) [1, 2]. During those studies, it appears
that the support for the mirror that reflects SR out of thevacuum deflects under thermal load from SR [3].
In the present work, we calculate the heat load on themirror of the booster synchrotron photon monitor at theAdvanced Photon Source (APS). We present the details ofthe mirror design. We summarise stability results using thediagnostic.

BACKGROUND
The beam profile monitors are required to support beam
size measurements of the electron beam in the booster. Threephoton ports are available for use as synchrotron light photon
monitors in the booster [4–7]. Previously, only two ports had
been instrumented. Under thermal loading, components of
the assembly supporting the mirror in these ports expanded
under thermal loading. The expansion was so significant
that the image of the beam was deflected off sensors used tomeasure the beam transverse and longitudinal dimensions [3,8]. Subsequently, this makes it difficult to routinely measuresome properties of the electron beam such as emittance andenergy spread.
∗ Work supported by the U.S. Department of Energy, Office of Sci-ence, Office of Basic Energy Sciences, under Contract No. DE-AC0206CH11357.
† kwootton@anl.gov

To support physics goals of measuring the emittance in thebooster, we propose to instrument all three photon monitors.
The position of the beam image on the beam profile monitors
needs to remain within a small enough displacement fromnominal that it does not move off laterally the imaging anddiagnostic devices.

SR POWER ON THE MIRROR
For an electron beam, the vertical distribution of SR powerd𝑃in units of [W mrad−2 ] is calculated by [9]:dΩ

5𝛾2 𝜓2d𝑃
1= 5.42𝐸 4 𝐵𝐼𝑏[1 +],
5/2dΩ
7 (1 + 𝛾2 𝜓2 )(1 + 𝛾2 𝜓2 )(1)
where 𝐸 is in units of [GeV], 𝐵 is in units of [T], 𝐼𝑏 is inunits of [A], 𝛾 is the Lorentz factor, and 𝜓 is the verticalangle in units of [rad].
d𝑃The peak power density (on-axis) dΩ
in units of−2[W mrad ] is given by [9]:d𝑃
= 5.42𝐸 4 𝐵𝐼𝑏 .
dΩ(2)Integrating over the vertical angle, the power density ind𝑃
the horizontal direction dΩ
in units of [W mrad−1 ] is givenby [9]:d𝑃
= 4.22𝐸 3 𝐵𝐼𝑏 .
(3)dΩCalculation

We propose to perform a piecewise integration of the SRpower, at intervals of 1 ms. Parameters used in the present
calculation are summarised in Table 1. These parameters areapproximate, and close to the nominal booster ramp [10–12].
Table 1: Booster and Electron Beam Parameters
Parameter
Booster circumference
ChargeBeam current
SR source to mirror
Bending radius
Energy at injection
Energy at extraction
Ramp time (𝐸𝑖 -𝐸𝑒 )Booster period
Photon port width
Photon port height

SymbolValueRef.

C𝑞𝐼𝑏𝑑𝜌
𝐸𝑖𝐸𝑒𝑡𝑟𝑇𝐵𝑤ℎ368 m
17 nC
13.9 mA
2.85 m33.3 m425 MeV
7.1 GeV0.25 s
1.0 s
60 mm
37 mm

[1]
[2]
…
…
[13]
…
…
…
…
…
…

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03 Transverse Profile and Emittance Monitors

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3ResultsFigure 1 shows the profile of electron beam energy as afunction of time during the ramp, using the parameters given
in Table 1. In Fig. 2, we plot the profile of the magnetic fieldwith the time during the ramp.

2001508100

650

402000.05

0.1

0.15

0.20.25

Figure 1: Beam energy as a function of time.

0.800.05

0.1

0.15

0.20.25

Figure 3: Peak SR power (Eq. (2)) as a function of time
during the booster ramp. Essentially, this is equivalent to aline profile through Fig. 5 at vertical position = 0 mm (theorbit plane of the beam).
15100.650.4
00.2
000.05

0.1

0.15

0.2

0.25

Figure 2: Magnetic field as a function of time.
Using Eq. (1), in Fig. 3 we plot the SR power as a functionof both time during the ramp and vertical position at thelocation of the mirror.
Using Eq. (2), we plot the peak SR power density (onaxis) as a function of time during the booster ramp. We seethat the dependence of SR power on the beam energy to thefourth power results in power deposition principally at thehighest beam energies in the ramp.
Using Eq. (3), we calculate the SR power integrated overthe full vertical fan, as a function of time. This is presentedin Fig. 4.
Using the trapezoidal rule, we numerically integrate thepower in Fig. 4, which gives 0.783 W mrad−1 (per unit horizontal bending angle). We can calculate the horizontal

00.05

0.1

0.15

0.2

0.25

Figure 4: Total SR power on the mirror (Eq. (3)) as a functionof time during the booster ramp.
angular size of the photon port as 𝑤/𝑑 = 21.1 mrad. Henceusing the product of the two, we can calculate the total poweron the chamber during the ramp to be 16.5 W (across thewhole width of the photon port). This is the power thatwould occur if the booster always had beam (duty factor of1). However, the duty factor is necessarily reduced, to accommodate ramping of the booster magnets, and stacking in
the upstream Particle Accumulator Ring. Hence, we define
a duty factor as 𝑡𝑟 /𝑇𝐵 = 0.25. Hence the time-averaged SR
power across the photon port is 4.1 W.

PROFILE MONITOR LAYOUT
The beam profile monitor optical path and principal components are illustrated schematically in Fig. 6.
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359

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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3IBIC2023, Saskatoon, Canada
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Figure 5: SR power distributed as a function of both time
during the ramp and vertical position at the location of themirror (Eq. (1)).

Figure 7: Photograph of beam profile monitor in the booster
ring.

Figure 6: Schematic of beam profile monitor in the booster
ring. (a) SR from electron beam. (b) Glidcop mirror. (c)Out-of-vacuum mirror. (d) Motorised zoom-focus lens. (e)Digital camera.
Components of the beam profile monitor are located physically within the booster synchrotron enclosure, which isillustrated in Fig. 7.

MirrorSince the average SR beam power on the mirror was small(4.1 W), we endeavoured to improve imaging stability using arigid mirror assembly composed of a bulk material. Glidcop
was selected as the mirror substrate material.
The mirror was fabricated and polished in-house. Themirror substrate was cut and then polished using Loose Abrasive Polishing (lapping) to achieve the desired mirror surface
finish. The mirror surface was specified as 60-40 scratch-dig,and a flatness error of 1𝜆. The mirror geometry is illustrated
in Fig. 8.
For polishing, lapping was performed in several stages.
The Glidcop Mirror and polishing fixture assembly weremounted in a precision vice on an Okamoto surface grinder

Figure 8: Mirror geometry.
(Fig. 9). The finished polished mirror is illustrated in Fig. 10.

IMAGE STABILITY
The principal goal of this mirror was to improve the image
stability under an increased thermal load. We have tested
the mirror performance in machine studies. For the existing
synchrotron light monitors (denoted 1 & 2), lateral drift in
the image position is observed as the mirrors distort underthermal loading from SR [3].
The most demanding beam condition under which we havetested the mirror is a 5 nC beam charge at 2 Hz repetition
rate. This represents an average SR power on the mirror of
2.4 W, which is representative compared to the design of
4.1 W. We seek to evaluate the performance of the mirror

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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 P 0 1 5108642Figure 9: Photograph of the mirror and polishing fixture
during machine lapping.

000.05

0.1

0.15

0.2

0.25

00.05

0.1

0.15

0.2

0.25

200
0-200-400

Figure 10: Finished mirror after final polishing.
stability under thermal load. We observed the electron beamsimultaneously using two synchrotron light monitors: anexisting synchrotron light monitor (B:SLM1) and this newmonitor using a new mirror (B:SLM3). The motion of thebeam image on both monitors is illustrated in Fig. 11.

SUMMARY
We have specified, designed and fabricated a mirror toobserve and image visible synchrotron light from the booster
synchrotron at the APS. We have calculated the SR power on
mirror under anticipated beam conditions for APS-U operations, giving a maximum SR power on the mirror of 4.1 W.
The mirror was fabricated and installed in the booster. We
have tested the mirror under representative thermal loading
and find that the mirror achieves the primary objective ofstably transporting the SR power without measurable distortion.

ACKNOWLEDGEMENTS
The submitted manuscript has been created by UChicago
Argonne, LLC, Operator of Argonne National Laboratory

Figure 11: Electron beam image centroid position measured
using two synchrotron light monitors. Over a 15 minute period, the centroid position on the old mirror (B:SLM1) drifts
significantly, while there is no measurable drift observed forthe new mirror design (B:SLM3).
(“Argonne”). Argonne, a U.S. Department of Energy Office of Science Laboratory, is operated under Contract No.
DE-AC02-06CH11357. The U.S. Government retains foritself, and others acting on its behalf, a paid-up nonexclusive,
irrevocable worldwide license in said article to reproduce,
prepare derivative works, distribute copies to the public, andperform publicly and display publicly, by or on behalf ofthe Government. The Department of Energy will provide
public access to these results of federally sponsored researchin accordance with the DOE Public Access Plan. http://energy.gov/downloads/doe-public-access-plan

REFERENCES[1] J. R. Calvey, M. Borland, K. C. Harkay, R. R. Lindberg, andC. Yao, “Simulations of Booster Injection Efficiency for theAPS-Upgrade,” in Proc. NAPAC’16, Chicago, IL, USA, Oct.
2016, pp. 647–650.
doi:10.18429/JACoW-NAPAC2016-WEA1CO03[2] K.C. Harkay et al., “High-Charge Injector for
on-Axis Injection Into A High-Performance Storage Ring Light Source,” in Proc. IPAC’19, Mel-WEP015
03 Transverse Profile and Emittance Monitors

361

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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 - 3IBIC2023, 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 P 0 1 5bourne, Australia, May 2019, pp. 3423–3426.
doi:10.18429/JACoW-IPAC2019-THYYPLM3[3] J. C. Dooling, W. Berg, J. R. Calvey, K. C. Harkay, and K. P.
Wootton, “Measurements of Bunch Length in the Advanced
Photon Source Booster Synchrotron”, in Proc. NAPAC’22,Albuquerque, NM, USA, Aug. 2022, pp. 394–397.
doi:10.18429/JACoW-NAPAC2022-TUPA22[4] B. Yang, A.H. Lumpkin, “The Planned Photon Diagnostics
Beamlines at the Advanced Photon Source”, AIP Conf. Proc.,vol. 333, no. 1, pp. 252–258, May 1995.
doi:10.1063/1.48048[5] B.X. Yang, A.H. Lumpkin, M. Borland, K. Harkay, and A.
Nassiri, “Characterization of Beam Dynamics in the APS
Injector Rings Using Time-Resolved Imaging Techniques”, inProc. PAC’97, Vancouver, Canada, May 1997, paper 5P040,
pp. 2052–2054.
https://jacow.org/pac97/papers/pdf/5P040.PDF[6] A. Lumpkin and B. Yang, “Status of the Synchrotron Radiation Monitors for the APS Facility Rings”, in Proc. PAC’95,Dallas, TX, USA, May 1995, paper MPQ09, pp. 2470–2472.
https://jacow.org/p95/ARTICLES/MPQ/MPQ09.PDF[7] A. Lumpkin et al., “Initial Diagnostics Commissioning Results for the Advanced Photon Source (APS)”, in Proc.
PAC’95, Dallas, TX, USA, May 1995, paper MPQ10,pp. 2473–2475.
https://jacow.org/p95/ARTICLES/MPQ/MPQ10.PDF[8] J.C. Dooling, J.R. Calvey, K.C. Harkay, private communication, Jan. 2022.
[9] R.P. Walker, “Synchrotron radiation,” CAS - CERN Accelerator School: 5th General Accelerator Physics Course (7-18 Sep.
1992, Jyväskylä, Finland), Technical Report CERN-94-01,
pp. 437-459, 1994. doi:10.5170/CERN-1994-001.437[10] S.V. Milton, J.A. Carwardine, “Ramp Tuning of the APS
Booster Synchrotron Magnet Power Supplies,” in Proc.
PAC’95, Dallas, TX, USA, May 1995, paper RPQ18,
pp. 2708–2710.
https://jacow.org/p95/ARTICLES/RPQ/RPQ18.PDF[11] J.A. Carwardine, S.V. Milton, D.G. McGhee, “Performanceof the Ramping Power Supplies for the APS Booster Synchrotron,” in Proc. PAC’95, Dallas, TX, USA, May 1995,
paper RPP03, pp. 1967–1969.
https://jacow.org/p95/ARTICLES/RPP/RPP03.PDF[12] C.-Y. Yao, B. Deriy, G. Feng, H. Shang, and J. Wang, “Upgrade of the APS Booster Synchrotron Magnet Ramp,” inProc. PAC’11, New York, NY, USA, Mar.-Apr. 2011, paper
TUP190, pp. 1181–1183.
https://jacow.org/PAC2011/papers/TUP190.pdf[13] B. Yang, private communication, Jan. 1998.

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