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BEAMLINE FOR TIME DOMAIN PHOTON DIAGNOSTICS
AT THE ADVANCED PHOTON SOURCE UPGRADE∗
K. P. Wootton† , W. Cheng, G. Decker, N. S. Sereno, F. Westferro
Argonne National Laboratory, Lemont, IL, USA
Abstract
Time domain photon diagnostics are proposed for electron beam characterisation and operation of the Advanced
Photon Source Upgrade storage ring. In the present work,we present updated status on the time-domain X-ray andvisible photon diagnostic beamline for the Advanced Photon Source Upgrade. We outline design influences leading
to the proposed beamline layout, in particular long-term
maintenance and commonality with other beamlines at theAdvanced Photon Source.

INTRODUCTION
The Advanced Photon Source Upgrade (APS-U) projectis presently underway, with the goal of increasing the brilliance of photon beams to user beamlines at the Advanced
Photon Source (APS) [1–3]. A number of user programs
take advantage of the fill pattern for time-resolved X-ray techniques. As these user programs are anticipated to continue
during APS-U operations, we are providing temporal photon beam diagnostics for the optimisation and diagnosticsof accelerator operations.
In the present work, we present updated status on the timedomain X-ray and visible photon diagnostic beamline at 35BM for the APS-U. We outline design influences leading
to the proposed beamline layout, in particular long-term
maintenance and commonality with other beamlines at theAPS.

DESIGN INFLUENCES
The beamline layout has matured through the design process, with subtle but notable changes since our previous
work on this beamline [4]. In particular, we have made aconcerted effort to utilise components standardised across
APS-U bending magnet front ends and beamlines to thegreatest extent possible.
For the APS, the 35-BM front-end and beamline employeda geometry optimised for providing multiple independent
photon beams for diagnostics [5, 6]. The beamline featured
three branch lines (X-ray, visible, X-ray) separated horizontally in angle from the bending magnet source. The visible
light beamline passed a large vertical angular acceptance of±2.9 mrad (Fig. 1). Several practical constraints steered us
away from adopting the existing 35-BM geometry directlyfor APS-U.
∗ 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

65432
10-3-2-1

01

23Figure 1: Vertical profile of bending magnet synchrotron
radiation accepted by 35-BM for APS storage ring. Thecold finger masks synchrotron radiation over the central±0.5 mrad.
It is envisaged that two diagnostic beamlines will be operated for routine beam diagnostics measurements for APS-U.
Transverse beam sizes and emittances will be observed using
the 38-AM bending magnet beamline [7–10]. Bunch lengthand bunch purity will be observed using visible light and
X-ray diagnostics at the 35-BM beamline [4]. To meet thelong-term need for time-domain diagnostics at 35-BM, alarge vertical aperture is not strictly required for either the
X-ray or visible light photon diagnostics. Hence rather thancreating large vertical opening apertures in many components of the 35-BM front end, we instead start our designfrom the new bending magnet front end (BMFE) for user
APS-U bending magnet beamlines [1]. The opening angleof visible synchrotron radiation and beamline apertures areillustrated in Fig. 2.
The choice to start from the standard user BMFE design
affords us opportunities to standardise many beamline components and control equipment. We anticipate that this will
be beneficial for long-term maintenance of the beamline.

FRONT END
35-BM has been operational as a diagnostic beamline at
APS for many years [5, 6]. We summarise features of theWEP016

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front end and beamline layout for APS-U. The beamline
front end for APS-U and APS is illustrated in Fig.3.

X-Ray Path

6Figure 3 shows the scope of the changes to the front endfor 35-BM. The standard BMFE is designed to pass X-rays
through the the beamline (and protect the beamline when
shutters are closed), so no changes to the standard BMFE
are needed to accommodate X-ray beam transport to theshielded enclosures of 35-BM.

54Visible Light Path

3For visible light, two essential changes are needed to thefirst fixed mask (FM1) and the visible light mirror. The
vertical aperture of FM1 was increased by modifying a completed FM1 assembly using wire-cut electrical dischargemachining. This increases the opening angle of synchrotron
radiation accepted by the beamline to ∼±0.35 mrad. The
enlarged machined aperture of FM1 is illustrated in Fig. 4.

2
10-3-2-10123Figure 2: Vertical profile of bending magnet synchrotron
radiation accepted by 35-BM for APS-U storage ring. The
vacuum chamber wall blocks synchrotron radiation at angles>±1.0 mrad. The first fixed mask (FM1) blocks synchrotron
radiation at angles >±0.35 mrad.

Figure 4: Machining of FM1 vertical aperture to increase thevertical aperture for visible light propagation. The narrower
slot (at right) is used to pass X-rays through to the X-ray
beamline enclosures. The beam direction in this figure isinto the page.

Figure 3: Comparison of 35-BM front ends for APS-U andAPS. The horizontal axis 𝑧 is the distance from the bending
magnet source in metres. (a) Front end configuration forAPS-U. (i) First Fixed Mask. (ii) Visible Light Mirror. (b)Front end configuration for APS.

A mirror inclined at 45∘ was used to reflect visible synchrotron radiation upwards. For APS [Fig. 3(b)], this mirror
was at 𝑧 ≈ 15 m, while for APS-U [Fig. 3(a)], we position
the new mirror at 𝑧 ≈ 19.8 m. This location was selected
because it replaces the second X-ray Beam Position Monitor(XBPM2) in the standard BFME [1]. A water-cooled andvertically translatable stage for XBPM2 provide the required
control for this optical mirror. The visible light mirror isshown installed in its vacuum chamber in Fig. 5.
Thermal analysis of the visible light mirror was performed
using finite element analysis. For routine beamline operations, we intend for the mirror to sit below the orbit planeof the ring, intercepting the lower fan of visible light synchrotron radiation in a manner similar to Refs. [11, 12]. Us-WEP016
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Figure 5: Visible light mirror. The beam direction in thisfigure is into the page.
ing the translatable vertical stage, the mirror can be moved
completely into the beam path to intercept visible light aboveand below the orbit plane of the ring, however this is anticipated to be used only for dedicated machine studies withvery low stored beam current.
Beyond the first mirror, visible light will be transported in
air by reflecting the light using planar mirrors to the opticalenclosure 35-BM-B. The optical transport is enclosed bystainless steel tubing.

BEAMLINE
The beamline layout on a standard APS sector is illustrated in Fig. 6. From the perspective of the X-ray beamline,
the most significant change between the APS and APS-U
machine is the lateral offset of 42 mm inboard of the new Xray source point [1]. As a result, the new beamline centerline
is 42 mm inboard of the previous beamline. Fortuitously,
35-BM features a unique shielded X-ray transport passing
through the 35-BM-B hutch. The beam transport is actually
two separate beam transport tubes, separated horizontally.
As a result, we are able to configure the beamline to employ
the inboard beam transport with minimal changes to thebeamline components. Beamline components are illustrated
in profile view in Fig. 7.

OUTLOOK
The principal long-term purpose of the X-ray beamline
configuration is to preserve X-ray beam transport from the35-BM-A through to 35-BM-C hutches, for use with thebunch purity monitor diagnostic [13,14]. However the beamline can also be used as configured for an X-ray pinhole camera for beam size measurements. Four blades of white-beamslits (𝑧 = 24 m) can be closed to form a rectangular pinhole

Figure 6: Illustration of 35-BM beamline layout for APS-U
operations. The horizontal axis 𝑧 is the distance from thebending magnet source in metres. The beam direction inthis figure is from top to bottom.
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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 6aperture. A scintillator and optical microscope can be positioned near the end of the beamline (𝑧 = 45 m) in orderto image the electron beam in the APS-U storage ring with
an X-ray pinhole magnification 21/24 = 0.875. Parametersof the electron beam and pinhole camera in the horizontal
plane are summarised in Table 1.
Table 1: Pinhole Camera Parameters
Parameter
Beta function
Emittance
Energy spread
Dispersion
Beam size (source)
Pinhole magnification
Beam size (scintillator)

Symbol

Value

𝛽𝑥
𝜀𝑥
𝛿
𝜂𝑥
𝜎𝑥
𝑀
Σ𝑥

0.84 m42 pm rad0.156%
3.67 mm
8.3 μm
0.875
7.2 μmWe anticipate that the spatial resolution needed to image
an X-ray spot size of Gaussian distribution Σ𝑥 = 7.2 μm is
challenging, but not beyond technical feasibility. We anticipate that few-μm resolution may be achievable by using a
20 μm thick single-crystal scintillator such as Cerium-doped
Yttrium Aluminium Garnet imaged by an optical microscopewith numerical aperture between 0.4–1.0 [15].

SUMMARY
In the present work, we have presented updated status on
the time-domain X-ray and visible photon diagnostic beamline for the Advanced Photon Source Upgrade. We haveoutlined design influences leading to the proposed beamline
layout, in particular long-term maintenance and commonality with other beamlines at the Advanced Photon Source.
Beyond its primary use as a time-domain diagnostic, weadditionally outline potential use of the beamline to image
the electron beam distribution in the horizontal plane.

ACKNOWLEDGEMENTS

Figure 7: Illustration of 35-BM beamline profile for APS-Uoperations. The horizontal axis 𝑧 is the distance from thebending magnet source in metres. The beam direction inthis figure is from top to bottom.

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

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