ELECTRON BEAM AT THE ADVANCED PHOTON SOURCE
LINAC EXTENSION AREA BEAMLINE
WEP017K.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

ABSTRACTSTAGES OF COMMISSIONINGMOTIVATION▪ The Linac Extension Area has beendeveloped into a beamline area for
testing accelerator components andtechniques.

▪ The Linac Extension Area (LEA) at theAdvanced Photon Source (APS) is aflexible beamline for accelerator component
and technique development [1-4].

▪ Beginning commissioning activities inFebruary 2023, we have delivered
the first electron beam to the LinacExtension Area at the Advanced
Photon Source at 425 MeV.

▪ Hardware installation was completed in
2023, and activities to commission theelectron beamline began in 2023.

▪ In the present work, we outline thestages of re-commissioning theelectron beamline.
▪ We summarise measurements of theelectron beam transport through theaccelerator.
▪ We outline scenarios used to verify
the adequacy of radiation shielding of
the beamline, and measured
shielding performance.

▪ The principal consideration in commissioning with the electron
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) [5-7], but it has been several years
since beam was introduced to the enclosure [8].
▪ This motivated the need for a readiness review prior tocommissioning the beamline in a staged approach.
Commissioning activities performed are broken into two stages:
transport to the BB dump, and transport to the LEA beamline.
▪ The electron source used for these commissioning tasks was thethermionic cathode radiofrequency electron gun (TCGun) rather
than the nominal photocathode radiofrequency electron gun(PCGun). TCGun is capable of generating the greatest electron
beam current and as such represents the principal radiologicalrisk needing experimental validation.

▪ In the present work, we summarise theprogress to date in commissioning the LEA
beamline.
▪ We outline the features of the LEA
beamline. We summarise the stages of recommissioning. We present measurementsof the electron beam using beamdiagnostics in the LEA enclosure during
stages of commissioning. We outline thebeam loss scenarios to be performed for
qualifying the enclosure shielding.

LEA BEAMLINE▪ The principal diagnostics used for thisstudy included area radiation
monitors, handheld portable radiation
monitors, electron beam position
monitors, beam profile monitors andbeam current monitors.

▪ The LEA beamline lattice is configured to support`interleaving' operation [9,10]. Interleaving describes
switching between TCGun as an electron source for
APS storage ring operations, and PCGun for LEA
operations. We denote the LEA beamline as thesection of beamline physically located within the LEA
enclosure. The LEA beamline is illustrated in Fig. 1.

▪ The first signature of electrontransport to LEA was observed usingFig. 5: First observation of electron beam in thearea radiation monitors. An area
LEA enclosure measured using signals on theelectron BPM.
radiation monitor is positioned within
the LEA enclosure. This was the firstindication that electrons had beensuccessfully transported. Signals
were subsequently quickly observedon the beam current monitors andbeam position monitors in the LEA
Fig. 6: Beam observed using BPMs along booster bypass andLEA. In this figure, the beam trajectory is from left to right.
enclosure. Signals on the first
Horizontal and vertical BPM signals are displayed. The horizontal
plot axis is BPM index: the BPMs are not equally spaced along
electron beam position monitor within the beamline. BPMs 23-26of thearebeamline.
the four BPMs in the LEA section
the LEA enclosure are illustrated inFig. 5.

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

▪ As presently installed, the LEA beamline itself occupies~15 m length within the LEA enclosure, terminatingwith an electron beam dump. A rendering of thebeamline in the enclosure is illustrated in Fig. 2. A
photograph of the LEA beamline is illustrated in Fig. 3.

Fig. 2: LEA enclosure. In this figure the beam direction is from right to left.

▪ The electron beam position wasobserved along the BB and LEA
beamlines using all the BPMs in bothtransport lines. This is illustrated inFig. 6.
Fig. 3: Photograph of the LEA beamline within the LEA enclosure. In this figure thebeam direction is from right to left.

▪ 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 asthe Particle Accumulator Ring bypass (PB), the PARto-Booster (PTB), and the Booster Bypass (BB)transport lines. The PAR bypass and PTB have beenpreviously used for electron beam transport, and so forcommissioning the LEA beamline, the main activity
needed was to establish electron beam transport
through the BB and LEA beamlines. A plan layout ofthe BB and LEA beamlines and the LEA enclosure areillustrated in Fig. 4.

BEAM LOSS SCENARIOSBEAM MEASUREMENTS

Fig. 4: Layout of Booster Bypass
and Linac Extension Areabeamlines. The electron beam
direction is upwards from thebottom of the page. Safety devices
are highlighted annotated.

OUTLOOK▪ Due to schedule constraints, we wereunable to complete measurement of thebeam loss scenarios prior to the long
shutdown of the APS accelerators tofacilitate the start of installation of theAdvanced Photon Source Upgrade(APS-U) storage ring.
▪ We hope to continue the commissioning
process again at a future date.

▪

A critical step in commissioning is validation of the shielding performance. At the APS, theshielding is experimentally validated using beam loss scenarios. Loss scenarios were meant toassess 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). 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. Steering beam horizontallyleft with corrector magnets.
7. Steering beam horizontally right with corrector magnets.
8. Steering beam vertically upwards with corrector and quadrupole magnets.
9. Steering beam horizontally left with corrector and quadrupole magnets.
10. 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 large transverse
offset of the electron beam from the centerline ofmultiple 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 theelectron beam at LEA was calculated over a rangeof electron beam energies 25–400 MeV. This is
illustrated in Fig. 8.
Subsequently, we can use these excursion angles
as input to radiological simulations. Radiologicalsimulations of these loss scenarios wereperformed 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. 9. This
simulations was performed assuming a 500 MeV
electron beam energy, scaled to a maximum
average electron beam current of 40 nA.
Maximum possible off-normal steering (verticalexcursion) of the electron is illustrated in Fig. 10.
This simulations was performed assuming a 300
MeV electron beam energy, scaled to a maximum
average electron beam current of 40 nA.
These scenarios were developed to understandthe safety consequences of proposed beamconditions. Of particular importance is that thenormal operational electron beam current from thePCGun (average 2 nA) is much lower thansimulated here for safety.

▪

▪ With beam transported through toLEA, we were able to begin tuning up
and focussing the electron beamusing the beam profile monitor
immediately adjacent to the electron
beam dump. The visible area of theCerium-doped Yttrium Aluminium
Garnet (Ce:YAG) scintillator is 16 mm
diameter. This is illustrated in Fig. 7.

▪

▪

Fig. 7: 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.

REFERENCES▪ We have observed first electron beam to the LEA
beamline at the APS.

[1]

▪ 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.

[4]▪ We began commissioning, but were unable to complete
measurement of the beam loss scenarios prior to the long
shutdown for APS-U installation.

Fig. 9: Radiological simulation of electron beam transport tothe electron beam dump (Scenario 2) [21]. In this figure, thebeam trajectory is into the page.

Fig. 10: Radiological simulation of maximum possible offnormal electron beam vertical missteer (Scenario 9) [21]. In
this figure, the beam trajectory is from right to left.

SUMMARY▪ We developed an extensive set of beam loss scenarios
taking advantage of new simulation techniques, andincorporating lessons learned from previous
commissioning activities.

Fig. 8: Calculated maximum excursion angleof electron beam at LEA [12].

[2]
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