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ELECTRON BEAM AT THE ADVANCED PHOTON SOURCE
LINAC EXTENSION AREA BEAMLINE∗K. P. Wootton† , W. J. Berg, M. Borland, A. Brill, J. M. Byrd, S. Chitra, J. Collins, J. C. Dooling,
J. Edwards, L. Erwin, G. Fystro, T. Grabinski, M. Henry, E. Heyeck, J. Hoyt, R. Keane, S.-H. Lee,
J. Lenner, I. Lobach, A. H. Lumpkin, A. Puttkammer, V. Sajaev, N. S. Sereno, Y. Sun, J. Wang,
S. G. Wang, A. A. Zholents, Argonne National Laboratory, Lemont, IL, USA
Abstract
The Linac Extension Area has been developed into a beamline area for testing accelerator components and techniques.
Beginning commissioning activities in February 2023, wehave delivered the first electron beam to the Linac Extension
Area at the Advanced Photon Source at 425 MeV. In thepresent work, we outline the stages of re-commissioning
the electron beamline. We summarise measurements of theelectron beam transport through the accelerator. We outline
scenarios used to verify the adequacy of radiation shieldingof the beamline, and measured shielding performance.

As presently installed, the LEA beamline itself occupies∼15 m length within the LEA enclosure, terminating with
an electron beam dump. A photograph of the LEA beamline
is illustrated in Fig. 2.

INTRODUCTION
The Linac Extension Area (LEA) at the Advanced Photon
Source (APS) is a flexible beamline for accelerator component and technique development [1–4]. Hardware installation was completed in 2023, and activities to commission
the electron beamline began in 2023.
In the present work, we summarise the progress to datein commissioning the LEA beamline. We outline the features of the LEA beamline. We summarise the stages ofre-commissioning. We present measurements of the electron beam using beam diagnostics in the LEA enclosure
during stages of commissioning. We outline the beam loss
scenarios to be performed for qualifying the enclosure shielding.

Figure 2: Photograph of the LEA beamline within the LEA
enclosure. In this figure the beam direction is from right toleft.

The LEA beamline lattice is configured to support ‘interleaving’ operation [5, 6]. Interleaving describes switching
between a thermionic cathode radiofrequency electron gun(TCGun) as an electron source for APS storage ring operations, and a photocathode radiofrequency electron gun(PCGun) for LEA operations. We denote the LEA beamline
as the section of beamline physically located within the LEA
enclosure. The LEA beamline is illustrated in Fig. 1.

The electron beam source for LEA is the APS linac. At
present, the APS linac is capable of providing electron beams
with energies up to ∼450 MeV. The electron beam is transported from the APS linac to the LEA enclosure by several
sections of beamline, denoted as the Particle Accumulator Ring bypass (PB), the PAR-to-Booster (PTB), and the
Booster Bypass (BB) transport lines. The PAR bypass and
PTB have been previously used for electron beam transport,
and so for commissioning the LEA beamline, the main activity needed was to establish electron beam transport throughthe BB and LEA beamlines. The lattice of the booster bypass
and LEA beamline for 425 MeV electrons is summarisedin Table 1. The magnet types XX:QX correspond to upright quadrupoles, and XX:BX to skew dipoles (verticallydeflecting). Numerous horizontal and vertical correctors arealso included in the beamlines, but omitted from Table 1 forreadability.

Figure 1: LEA beamline. In this figure the beam direction
is from left to right.

STAGES OF COMMISSIONING

LEA BEAMLINE∗ 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

The principal consideration in commissioning with theelectron beam is that the LEA beamline is located within the
LEA enclosure. This enclosure had previously been used for
the Low-Energy Undulator Test Line (LEUTL) [7–9], but it

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Table 1: Booster Bypass, Alcove and LEA Lattice
Element

Position 𝑠(m)Length 𝑙(m)Gradient

BB:QE1
BB:QE2
BB:Q1
BB:BM:1-1
BB:BM:1-2
BB:BM:1-3
BB:Q2
BB:Q3
BB:Q4
BB:BM:2-1
BB:BM:2-2
BB:BM:2-3
BB:Q5
BB:Q6
LA:Q1
LA:Q2
LEA:Q1
LEA:Q2
LEA:Q3
LEA:Q4
LEA:Q5
LEA:Q6
LEA:Q7
LEA:BD

20.87221.39921.98922.38322.55322.72331.18440.37949.57457.99358.16358.33358.76960.64268.04569.19874.18675.19076.11279.05380.00481.00481.66682.274

0.153
0.153
0.153
0.110
0.110
0.110
0.153
0.153
0.153
0.110
0.110
0.110
0.153
0.153
0.153
0.153
0.100
0.153
0.100
0.100
0.153
0.153
0.153
0.500

4.75 T m−1-5.95 T m−1
2.55 T m−1-9.36 mrad-9.36 mrad-9.36 mrad
-1.48 T m−1
0.93 T m−1-1.48 T m−1
9.36 mrad9.36 mrad9.36 mrad
2.83 T m−1-5.17 T m−1
3.05 T m−1
4.21 T m−1
8.72 T m−1-7.61 T m−1
3.90 T m−1
9.07 T m−1-7.16 T m−1
7.31 T m−1-5.79 T m−1
200 mradhas been several years since beam was introduced to the enclosure [10]. This motivated the need for a readiness review
prior to commissioning the beamline in a staged approach.
Commissioning activities performed are broken into twostages: transport to the BB dump, and transport to the LEA
beamline. The electron source used for these commissioning
tasks was TCGun rather than the nominal PCGun. TCGun iscapable of generating the greatest electron beam current andas such represents the principal radiological risk needing
experimental validation.

Beam Transport to BB Dump
The BB dump is essentially located at the start of the BB
transport line. This allows us to tune up beam transport
through the upstream PB and PTB transport lines. Beamtransport to the BB dump was established using diagnostics
along the beam transport line. The principal diagnostics
used in these studies were beam position monitors and beamprofile monitors. The principal optimisation needed to establish beam through to the BB dump was transverse steering
using corrector magnets.

Beam Transport to LEA
Transporting beam to LEA requires transporting beamthrough the BB and LEA beamlines. The booster bypass
beamline is a vertical chicane rising in elevation by ∼1 mover a length of ∼40 m. Focussing quadrupoles are included

within the lattice. We began beam transport by tuning thevertical bending magnets to optimise electron transport at abeam energy of 425 MeV.

BEAM MEASUREMENTS
The principal diagnostics used for this study included area
radiation monitors, handheld portable radiation monitors,
electron beam position monitors, beam profile monitors andbeam current monitors.
The first signature of electron transport to LEA was observed using area radiation monitors. An area radiation
monitor is positioned within the LEA enclosure. This was
the first indication that electrons had been successfully transported. Signals were subsequently quickly observed on the
beam current monitors and beam position monitors (BPMs)
in the LEA enclosure. Signals on the first electron beam
position monitor within the LEA enclosure are illustrated inFig. 3.

Figure 3: First observation of electron beam in the LEA
enclosure measured using signals on the electron BPM.
The electron beam position was observed along the BB
and LEA beamlines using all the BPMs in both transportlines. This is illustrated in Fig. 4.
With beam transported through to LEA, we were able tobegin tuning up and focussing the electron beam using thebeam profile monitor immediately adjacent to the electron
beam dump. The visible area of the Cerium-doped Yttrium
Aluminium Garnet (Ce:YAG) scintillator is 16 mm diameter.
This is illustrated in Fig. 5.

BEAM LOSS SCENARIOSA critical step in commissioning is validation of the shielding performance. At the APS, the shielding is experimentally
validated using beam loss scenarios. Loss scenarios weremeant to assess the radiation levels in and around the LEA enclosure under ‘normal’ and ‘off-normal’ beam conditions. It
was not our intention to evaluate losses in previously commissioned transport beamlines upstream of LEA (PB, PTB, BB).
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10
5
0
-5
-10

5

10

15

20

25

Figure 4: Beam observed using BPMs along booster bypass
and LEA. In this figure, the beam trajectory is from left toright. Horizontal and vertical BPM signals are displayed.
The horizontal plot axis is BPM index: the BPMs are notequally spaced along the beamline. BPMs 23-26 are the four
BPMs in the LEA section of the beamline.
The loss scenarios considered included:
1. No acceleration of beam in the linac (background)
2. Beam to the LEA beam dump (nominal operations)
3. Beam strike on gate valve (GV) 1, GV1.
4. Beam strike on GV3.
5. Steering beam vertically upwards with corrector magnets.
6. Steering beam vertically downwards with corrector
magnets.
7. Steering beam horizontally left with corrector magnets.
8. Steering beam horizontally right with corrector magnets.
9. Steering beam vertically upwards with corrector andquadrupole magnets.
10. Steering beam horizontally left with corrector andquadrupole magnets.
11. Steering low-energy beam vertically upwards with corrector and quadrupole magnets.
In developing these scenarios, particular attention was
paid to the possibility of oversteering a low energy beam [11].
In this case, the assumed deflection would arise from a largetransverse offset of the electron beam from the centerlineof multiple quadrupole magnets. The maximum potential
angular excursion of an electron beam was determined using
simulations in the code ELEGANT [12–14].
In simulation, we considered the possibility of transporting electrons with energy as low as 25 MeV to the LEA
enclosure. Using 3D field maps of the quadrupole and corrector magnets, the maximum excursion angle of the electron

Figure 5: Observing electron beam at Ce:YAG LEA dump
beam profile monitor. The top panel shows the image withthe electron beam on, the middle panel shows an image withthe electron beam off. The lower panel is the difference,
showing the electron beam distribution.

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Figure 6: Calculated maximum excursion angle of electron
beam at LEA [12].
beam at LEA was calculated over a range of electron beamenergies 25–400 MeV. This is illustrated in Fig. 6.
Subsequently, we can use these excursion angles as input
to radiological simulations. Radiological simulations ofthese loss scenarios were performed using MARS [15–18]
and FLUKA [19, 20]. We consider several scenarios.
Normal operation of the electron beam transported to theelectron beam dump is illustrated in Fig. 7. This simulations was performed assuming a 500 MeV electron beamenergy, scaled to a maximum average electron beam currentof 40 nA.

Figure 8: Radiological simulation of maximum possible
off-normal electron beam vertical missteer (Scenario 9) [21].
In this figure, the beam trajectory is from right to left.

OUTLOOK
Due to schedule constraints, we were unable to complete
measurement of the beam loss scenarios prior to the long
shutdown of the APS accelerators to facilitate the start of
installation of the Advanced Photon Source Upgrade (APSU) storage ring. We hope to continue the commissioning
process again at a future date.

SUMMARY
We have observed first electron beam to the LEA beamline at the APS. During commissioning activites, diagnostics
including radiation monitors, beam position monitors, beam
current monitors and beam profile monitors were usefully
employed to detect and optimise the electron beam. We
developed an extensive set of beam loss scenarios taking
advantage of new simulation techniques, and incorporating
lessons learned from previous commissioning activities. We
began commissioning, but were unable to complete measurement of the beam loss scenarios prior to the long shutdown
for APS-U installation.

ACKNOWLEDGEMENTS
Figure 7: Radiological simulation of electron beam transport
to the electron beam dump (Scenario 2) [21]. In this figure,the beam trajectory is into the page.
Maximum possible off-normal steering (vertical excursion) of the electron is illustrated in Fig. 8. This simulations was performed assuming a 300 MeV electron beamenergy, scaled to a maximum average electron beam currentof 40 nA.
These scenarios were developed to understand the safety
consequences of proposed beam conditions. Of particularimportance is that the normal operational electron beam
current from the PCGun (average 2 nA) is much lower thansimulated here for safety.

We gratefully acknowledge the computing resources provided on Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center at
Argonne National Laboratory.
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 of
the 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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