Opportunities with plasma-accelerated electrons at LESA

Hezin Serez Kaya, Boğaziçi University

Thamine Dalichaouch, UCLA

Peter Kicsiny, Yuri Nosochkov, Spencer Gessner, SLAC

Injectors and Beam Physics Workshop

September 15, 2026

What is LESA?

The Linac to End Station A (LESA) beamline delivers 4-8 GeV beams from LCLS-II to End Station A (ESA).

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LCLS-II makes 10x more electron beam than can be sent to the undulators.

• The rest goes to the dump!

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SLAC has previously hosted a Test Beam Program for detector development in ESA.

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LESA will accommodate both a Test Beam program and the LDMX dark matter experiment.

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The LESA users only require 1 electron per pulse.

LESA Overview

LESA Overview

What’s the plan for LESA?

LDMX at LESA

The Light Dark Matter eXperiment (LDMX) searches for dark matter particles with a “missing momentum” signature.

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Normally, electrons emit a bremsstrahlung photon when they hit the target. The signal is a deflected electron without a gamma-ray photon.

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LDMX tags each incoming electron individually, so it can only handle one electron at a time.

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LDMX requires 1E15 electrons-on-target (EOT) for the full program. A year has 1E7 seconds.

arXiv:2508.11833

Test Beams at LESA

https://indico.slac.stanford.edu/event/9874/

Test Beam workshop held at SLAC in early September.

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Highlighted unique capabilities for LESA and test in End Station A.

• Well-defined beams (e.g. excellent timing resolution) compared to other facilities.
• High rep-rate testing.
• Max energy 8 GeV.

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Representatives from DESY, CERN, and Fermilab test beam programs presented on their programs. CERN and Fermilab will be down for upgrades for several years.

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HEP wants to ramp up detector testing for FCC-ee.

Future Demands for Test Beam Facility

The FCC-ee drives demand for electron beam test facilities for the coming decades.

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FCC-ee calorimeters are design to measure >45 GeV particle energy.

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“5D” calorimetry is a new idea for time-resolved calorimetry.

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Detector tests will benefit from:

• 45 GeV electron beam energy
• 1%-level energy uncertainty
• 10 ps-level timing information

US FCC Workshop Link

US FCC Workshop Link

Global Test Beam Facilities

https://science.osti.gov/-/media/hep/hepap/pdf/Meetings/2024/December/HEPAP_Testbeams_120524.pdf

Global Test Beam Facilities

https://science.osti.gov/-/media/hep/hepap/pdf/Meetings/2024/December/HEPAP_Testbeams_120524.pdf

None of these facilities provide the combination of high energy, precise energy resolution, and timing information desired by FCC-ee detector tests.

Can we use plasma to boost the LESA beam energy?

Plasma Acceleration at FFTB and FACET

Relatively easy to achieve a high-energy electrons in a continuous spectrum.

FFTB (1999-2006)

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“Energy Doubling” experiment.

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42 GeV → 84 GeV

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Continuous spectrum of electrons

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Blumenfeld et al, Nature (2007)

FACET (2010-2016)

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“More than Energy Doubling” experiment.

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20 GeV → 50 GeV

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Continuous spectrum of electrons

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Corde et al., Nat. Comm. (2016)

Proposal: Plasma-Boosted Electrons at LESA

The LCLS-II beams are high-quality and can drive strong wakes in dense plasmas.

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We propose a plasma cell in the S30XL beamline that will boost the energy of electrons in the tail of the LCLS-II bunch.

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We expect to deliver “few” electrons with energy in excess of 20 GeV, with the 8 GeV LCLS-II bunch as the driver.

Plasma cell in this region

QPAD simulations with ideal LCLS-II beams

Prop. dir.

Peak decel.

8 GeV/m

Peak accel.

32 GeV/m

Simulation Parameters - QPAD Code

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Beam

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E = 8 GeV

𝜎_z = 10 μm

ε_x,y = 0.5 μm

β_x,y = 0.5 m

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Plasma

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n₀ = 4✕10¹⁷ cm^-3

L = 1 m

H. Serez Kaya

T. Dalichouch

QPAD simulations with ideal LCLS-II beams

H. Serez Kaya

T. Dalichouch

Some electrons in tail accelerated to 40 GeV.

Simulation Parameters - QPAD Code

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Beam

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E = 8 GeV

𝜎_z = 10 μm

ε_x,y = 0.5 μm

β_x,y = 0.5 m

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Plasma

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n₀ = 4✕10¹⁷ cm^-3

L = 1 m

QPAD simulations with ideal LCLS-II beams

H. Serez Kaya

T. Dalichouch

Use bends and collimators to select only highest energy electrons.

Some electrons in tail accelerated to 40 GeV.

Simulation Parameters - QPAD Code

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Beam

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E = 8 GeV

𝜎_z = 10 μm

ε_x,y = 0.5 μm

β_x,y = 0.5 m

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Plasma

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n₀ = 4✕10¹⁷ cm^-3

L = 1 m

Implementation in S30XL/LESA Beamline

There is plenty of space in the S30XL beamline to install a plasma source.

Can we focus the beam down to the small spot needed to drive a wake in a high density plasma?

Challenges:

• Residual dispersion in both planes.
• Large betafunctions in transfer line.

Solutions:

• Modify kicker+septum to act as dogleg with dispersion cancellation.
• Add quadrupoles, and possibly PMQs on a stage, to transfer line.

Dispersion

Implementation in LESA Beamline

Start

Rolled dipole

Transfer line

Transfer line

First A-line dipole

Septum Magnet

R&D at FACET-II?

Blumenfeld et al, Nature (2007)

Corde et al., Nat. Comm. (2016)

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R&D at FACET-II?

Blumenfeld et al, Nature (2007)

Corde et al., Nat. Comm. (2016)

Can we simulate the LCLS-II bunch?

• Match the density or peak current?

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Work within the context of E300/E301?

• Or a new experimental proposal?

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Key measurements:

• High transformer ratio
• Stability/tolerance studies
• dN/dE at highest energies
• Single electron detection

LESA as a Beam Test Facility?

A-Line Upgrade

A-Line Upgrade

Challenges:

Big ol’ magnets

Few quads

Large R₅₆

No chromatic correction

Few diagnostics

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Solution:

Multi-bend achromat upgrade

Conclusion

• First HEP application of plasma accelerated electrons.
• The delivery of single, high-energy electrons is much simpler than high-quality drive-witness acceleration.
• Relaxed tolerances on all parameters.
• Critical R&D demonstrations can be performed at FACET-II.
• Scale down FACET-II bunch charge to mimic LCLS-II.
• A plasma cell in S30XL allows for other exciting R&D opportunities.
• “Minimal” changes to S30XL O($1M) would enable this work.
• Further modifications to A-line O($10M) could transform ESA into a Beam Test Facility.

We are well-positioned to deliver very high energy electrons to LESA on a few-year time scale!

Backup

Additional R&D at LESA

S30XL and LESA provide a unique opportunity for accelerator R&D with the high-quality LCLS-II beams. R&D items include:

• Plasma energy booster for very hard x-rays.
• Plasma brightness transformer.
• MHz plasma acceleration, including tests of plasma source technology.

Test Beam Program at ESA (Carsten Hast)

Program ended in 2019

Plan to restart in 2027

g-2 Calorimeter (Previous Program)

Plasma Wakefield R&D Facilities at SLAC

Plasma at FFTB (1999-2006)

FACET (2010-2016)

FACET-II (2020–)

Plasma Wakefield Acceleration

Witness beam

The drive beam deposits energy in the plasma and creates the wakefield.

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The witness beam rides the wakefield and gains energy.

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Accelerating gradients are typically measured in GeV/m.

The drive-witness scheme requires precise 6D control of each of the beam parameters.

Plasma Acceleration at FACET and FACET-II

Significant progress on beam quality, but not without challenges!

FACET (2010-2016)

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First high-efficiency, two-bunch acceleration demonstrated in plasma.

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E_gain = 2 GeV

𝜎_E = 2%

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M. Litos et al, Nature (2014)

FACET-II (2020--)

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High-efficiency and high-quality two-bunch acceleration.

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E_gain = 6 GeV

𝜎_E = 0.69%

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Significant improvements in energy spread and charge capture compared to FACET results.

D. Storey et al. In prep.

Plasma Wakefield Acceleration

Witness tail

Alternatively, a long drive beam can self-accelerate its own tail.

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The result is a continuous spectrum of accelerated electrons.

This scheme is self-aligning and simpler to achieve experimentally.

Next Steps and Roadmap

Optimize plasma simulations for realistic beam parameters and lattice constraints.

Simulation

Plasma and beam transport simulations incl. collimation.

Include beam jitter effects, based on measurements in S30XL.

R&D at FACET

High energy gain experiments with few-electron diagnostics.

Scaled demonstration at FACET-II.

Development of discharge plasma source in collaboration with BELLA.

Engr. for LESA

Now

+3 years

+2 years

Scout candidate locations.

Services, RP considerations, chamber design.

Engineering drawings.

Install and commissioning.

White paper within 1 year