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FACET-II Science Overview

What we are trying to do at FACET-II

June 19, 2024

Facility for Advanced

Accelerator Experimental Tests

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An introduction to the FACET-II accelerator

June 19, 2024 R. Ariniello FACET-II Science Overview

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Accelerator layout

June 19, 2024 R. Ariniello FACET-II Science Overview

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Injector

June 19, 2024 R. Ariniello FACET-II Science Overview

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Copper Cathode

E

Copper Cathode

E

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LINAC and bunch compressors

June 19, 2024 R. Ariniello FACET-II Science Overview

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FACET-II produces very high peak current beams

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Overview of the experimental area

June 19, 2024 R. Ariniello FACET-II Science Overview

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FACET-II is a user facility – scientists propose experiments

Lots of experiments already planned for FACET-II (and more not included here!):

June 19, 2024 R. Ariniello FACET-II Science Overview

7

Proposal No.	Title
E-300	Plasma wakefield acceleration
E-301	Tailored plasma sources for plasma wakefield acceleration
E-308	Extreme focusing with a passive thin plasma lens
E-325	Automatic tuning for PWFA optimization
E-304	Density down ramp injection in PWFA
E-310	Trojan horse injection
E-311	Plasma torch optical density down ramp injection
E-338	Attosecond XUV/X-ray sources driven by PWFA
E-320	Strong field QED
E-332	Near field CTR based focusing of beams – laser-less SFQED
E-305	Beam filamentation and bright gamma ray bursts
E-336	Beam interactions with carbon nanotube materials
E-315	Plasma afterglow attosecond metrology
E-324	Optical visualization of plasma wakefield acceleration
E-326	Non-intercepting beam diagnostics
E-327	Virtual diagnostics for phase space prediction
E-331	Neural network-based tuning

Plasma wakefield acceleration

Strong field quantum electrodynamics

Strong field physics

Accelerator diagnostics

X-ray source application of PWFA

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FACET-II plasma wakefield acceleration experiments

Lots of experiments already planned for FACET-II (and more not included here!):

June 19, 2024 R. Ariniello FACET-II Science Overview

8

Proposal No.	Title
E-300	Plasma wakefield acceleration
E-301	Tailored plasma sources for plasma wakefield acceleration
E-308	Extreme focusing with a passive thin plasma lens
E-325	Automatic tuning for PWFA optimization
E-304	Density down ramp injection in PWFA
E-310	Trojan horse injection
E-311	Plasma torch optical density down ramp injection
E-338	Attosecond XUV/X-ray sources driven by PWFA
E-320	Strong field QED
E-332	Near field CTR based focusing of beams – laser-less SFQED
E-305	Beam filamentation and bright gamma ray bursts
E-336	Beam interactions with carbon nanotube materials
E-315	Plasma afterglow attosecond metrology
E-324	Optical visualization of plasma wakefield acceleration
E-326	Non-intercepting beam diagnostics
E-327	Virtual diagnostics for phase space prediction
E-331	Neural network-based tuning

Plasma wakefield acceleration

Strong field quantum electrodynamics

Strong field physics

Accelerator diagnostics

X-ray source application of PWFA

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Plasma wakefield acceleration

Accelerators are useful, but large and expensive
Make them smaller and more efficient to build more, or more powerful

June 19, 2024 R. Ariniello FACET-II Science Overview

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Precision Higgs and top quark studies

Physics beyond the standard model

Condensed matter

AMO

Biology

Colliders

Light sources

LHC: 27km accelerator

€7.5 billion

CERN

8.6km

3km

SLAC

LCLS-II

LCLS

LCLS FEL: 2x 1km accelerators

$1 billion for LCLS-II

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Why are high energy accelerators so large?

June 19, 2024 R. Ariniello FACET-II Science Overview

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The largest field demonstrated in conventional RF cavities is 50 MV/m.

The limit is dielectric breakdown of the cavity.

SLAC linac is 22 MV/m.

Circular proton accelerators are limited by the magnetic field of the bending magnets.

Cockcroft et al. (1999)

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Plasma-based accelerators won’t breakdown

June 19, 2024 R. Ariniello FACET-II Science Overview

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Contains and shapes EM waves

Generates fields by charge separation and plasma currents

D. Gavela et al. IPAC Proceedings (2014) and Berkeley Lab Laser Accelerator BELLA

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Plasma wakefield acceleration

June 19, 2024 R. Ariniello FACET-II Science Overview

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Drive Beam

Witness Beam

1.5nC

10GeV

15J

0.5nC

10GeV

5J

+ + + + + + + + + + + + + + +

- - - - - - - - - - - - - -

Both beams travel to the right at about

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Plasma wakefield acceleration

June 19, 2024 R. Ariniello FACET-II Science Overview

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+ + + + + + + + + + + + + + +

- - - - - - - - - - - - - -

Both beams travel to the right at about

The electron beams have strong, radial electric fields

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Plasma wakefield acceleration

June 19, 2024 R. Ariniello FACET-II Science Overview

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+ + + + + + + + + + + + + + +

- - - - - - - - - - - - - -

- - - - - - - - - - - -

- - - - - - - - - -

- - - - - - - - -

- - - - - - - - - -

- - - - - - - - - - - -

- - - - - - - - - - - - - -

Both beams travel to the right at about

-

Light electron pushed radially, heavy ions stationary

-

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Plasma wakefield acceleration

June 19, 2024 R. Ariniello FACET-II Science Overview

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+ + + + + + + + + + + + + + +

- - - - - - - - - - - - - -

- - - - - - - -

- - - - -

- - -

- - - - -

- - -

- - - - -

- - - - - - - - -

- - - - - - - - - - - - - -

Both beams travel to the right at about

-

Electrons return to the axis, attracted by the ions

-

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Plasma wakefield acceleration

June 19, 2024 R. Ariniello FACET-II Science Overview

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+ +

+ + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + +

+ +

- - -

- -

-

- - -

-

- -

- - - -

- - -

Both beams travel to the right at about

-

Electrons return to the axis, attracted by the ions

-

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Plasma wakefield acceleration

June 19, 2024 R. Ariniello FACET-II Science Overview

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Drive Beam

Witness Beam

1.5nC

0.5GeV

0.75J

0.5nC

20GeV

10J

Drive beam lost 14.25J, witness beam gained 5J

Efficiency: 5/14.25 = 35%

Plasma wakefield accelerator transfers energy from the drive beam to the witness.

+ + + + + + + + + + + + + + +

- - - - - - - - - - - - - -

- - - - - - -

- - -

- - - - - - - - -

- - - - - - - - - - - - - -

-

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How strong are the fields?

Size of the plasma wave scales as

Electric field scales as

June 19, 2024 R. Ariniello FACET-II Science Overview

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There is a GV/m in there!

Reminder: conventional linac is maybe 50 MV/m.

1 km accelerator in 1m.

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State of the art conventional vs. plasma

June 19, 2024 R. Ariniello FACET-II Science Overview

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Parameter	Conventional (LCLS)	Plasma Based
Energy	10 GeV	9 GeV
Gradient	22 MeV/m	50 GeV/m
Charge	0.25 nC	0.1 nC
Energy Spread	0.1%	0.13%
Emittance	1 um-rad	2.75 um-rad

✔

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State of the art conventional vs. plasma

June 19, 2024 R. Ariniello FACET-II Science Overview

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Parameter	Conventional (LCLS)	Plasma Based
Energy	10 GeV	9 GeV
Gradient	22 MeV/m	50 GeV/m
Charge	0.25 nC	0.1 nC
Energy Spread	0.1%	0.13%
Emittance	1 um-rad	2.75 um-rad

✔

Experiments have only achieved 3 at a time!

Other Parameters
Emittance? We don’t talk about that
6% energy spread, 6 pC
0.1 nC
45 MeV gain on a 1 GeV beam
35 MeV gain on a 1 GeV beam

Total efficiency is low in experiments.

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Scientific goals for PWFA at FACET-II

Start with 0.5 nC witness beam
High total efficiency

Deplete all the energy from the drive beam
Accelerate the witness beam to high energy

Emittance preservation

Emittance doesn’t grow during acceleration

Reasonable energy spread

Better than a couple percent

Put it all together

June 19, 2024 R. Ariniello FACET-II Science Overview

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Ideal PWFA at FACET-II

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Energy evolution of drive and trailing bunches:

Energy Doubling (10-20+ GeV) with:

<1% Energy Spread,
Pump Depletion and > 40% pump to trailing bunch energy transfer efficiency,
while minimizing emittance growth

C. Joshi, et al., Plasma Physics and Controlled Fusion 60 (2018) 034001

Plasma and beam density with on-axis Ez line out:

Drive Bunch

Trailing Bunch

Drive

Bunch

Trailing

Bunch

Energy Doubling

Slide from Doug Storey

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Other things that can be done with PWFA – injection

June 19, 2024 R. Ariniello FACET-II Science Overview

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+ +

+ + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + +

+ +

- - -

- -

-

- - -

-

- -

- - - -

- - -

Both beams travel to the right at about

-

Only have the drive beam to start

-

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Other things that can be done with PWFA – injection

June 19, 2024 R. Ariniello FACET-II Science Overview

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+ +

+ + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + +

+ +

- - -

- -

-

- - -

-

- -

- - - -

- - -

Both beams travel to the right at about

-

Create a second electron beam in the wake

-

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Many ways to create an electron beam in the wake

Electron beams typically have very nice properties

June 19, 2024 R. Ariniello FACET-II Science Overview

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Goal of injection experiments: make nice beams!

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Other things that can be done with PWFA – plasma lens

June 19, 2024 R. Ariniello FACET-II Science Overview

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Other things that can be done with PWFA – plasma lens

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First goal is to observe strong focusing matching theory.

Second goal is to probe fundamental limits to focusing.

Plasma off

Plasma on

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FACET-II applications of PWFA

Lots of experiments already planned for FACET-II (and more not included here!):

June 19, 2024 R. Ariniello FACET-II Science Overview

28

Proposal No.	Title
E-300	Plasma wakefield acceleration
E-301	Tailored plasma sources for plasma wakefield acceleration
E-308	Extreme focusing with a passive thin plasma lens
E-325	Automatic tuning for PWFA optimization
E-304	Density down ramp injection in PWFA
E-310	Trojan horse injection
E-311	Plasma torch optical density down ramp injection
E-338	Attosecond XUV/X-ray sources driven by PWFA
E-320	Strong field QED
E-332	Near field CTR based focusing of beams – laser-less SFQED
E-305	Beam filamentation and bright gamma ray bursts
E-336	Beam interactions with carbon nanotube materials
E-315	Plasma afterglow attosecond metrology
E-324	Optical visualization of plasma wakefield acceleration
E-326	Non-intercepting beam diagnostics
E-327	Virtual diagnostics for phase space prediction
E-331	Neural network-based tuning

Plasma wakefield acceleration

Strong field quantum electrodynamics

Strong field physics

Accelerator diagnostics

X-ray source application of PWFA

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Application of PWFA beam – attosecond X-ray source

June 19, 2024 R. Ariniello FACET-II Science Overview

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C. Emma et al., APL Photonics, 6, 076107 (2021)

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Application of PWFA beam – attosecond X-ray source

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Demonstrate post-plasma sub-fs compression of e- beams.

Measure + characterize XUV CSR for compressed e- beam.

Slide from Claudio Emma

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FACET-II strong field quantum electrodynamics experiments

Lots of experiments already planned for FACET-II (and more not included here!):

June 19, 2024 R. Ariniello FACET-II Science Overview

31

Proposal No.	Title
E-300	Plasma wakefield acceleration
E-301	Tailored plasma sources for plasma wakefield acceleration
E-308	Extreme focusing with a passive thin plasma lens
E-325	Automatic tuning for PWFA optimization
E-304	Density down ramp injection in PWFA
E-310	Trojan horse injection
E-311	Plasma torch optical density down ramp injection
E-338	Attosecond XUV/X-ray sources driven by PWFA
E-320	Strong field QED
E-332	Near field CTR based focusing of beams – laser-less SFQED
E-305	Beam filamentation and bright gamma ray bursts
E-336	Beam interactions with carbon nanotube materials
E-315	Plasma afterglow attosecond metrology
E-324	Optical visualization of plasma wakefield acceleration
E-326	Non-intercepting beam diagnostics
E-327	Virtual diagnostics for phase space prediction
E-331	Neural network-based tuning

Plasma wakefield acceleration

Strong field quantum electrodynamics

Strong field physics

Accelerator diagnostics

X-ray source application of PWFA

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Strong field QED

June 19, 2024 R. Ariniello FACET-II Science Overview

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Observe evidence of non-perturbative quantum electrodynamics.

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Collide an electron beam with a laser

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Observe energy spectrum of electrons showing inverse Compton scattering.

Observe positrons from pair production.

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Colliding an electron beam with a plasma

Reflected self fields exceed Schwinger field in the beam rest frame

June 19, 2024 R. Ariniello FACET-II Science Overview

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A. Matheron, et al., Commun Phys (2023)

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Nonlinear QED processes in the collision

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A. Matheron, et al., Commun Phys (2023)

Quantum nonlinear inverse Compton scattering

Nonlinear pair production e-

Nonlinear pair production e+

Evolution in time

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Reaching beam sizes necessary for SFQED

June 19, 2024 R. Ariniello FACET-II Science Overview

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Demonstrate focusing of the beam to small sizes by colliding with multiple foils.

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FACET-II strong field physics

Lots of experiments already planned for FACET-II (and more not included here!):

June 19, 2024 R. Ariniello FACET-II Science Overview

37

Proposal No.	Title
E-300	Plasma wakefield acceleration
E-301	Tailored plasma sources for plasma wakefield acceleration
E-308	Extreme focusing with a passive thin plasma lens
E-325	Automatic tuning for PWFA optimization
E-304	Density down ramp injection in PWFA
E-310	Trojan horse injection
E-311	Plasma torch optical density down ramp injection
E-338	Attosecond XUV/X-ray sources driven by PWFA
E-320	Strong field QED
E-332	Near field CTR based focusing of beams – laser-less SFQED
E-305	Beam filamentation and bright gamma ray bursts
E-336	Beam interactions with carbon nanotube materials
E-315	Plasma afterglow attosecond metrology
E-324	Optical visualization of plasma wakefield acceleration
E-326	Non-intercepting beam diagnostics
E-327	Virtual diagnostics for phase space prediction
E-331	Neural network-based tuning

Plasma wakefield acceleration

Strong field quantum electrodynamics

Strong field physics

Accelerator diagnostics

X-ray source application of PWFA

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Beam filamentation instability

Relativistic plasma instability

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Goals: Understand relativistic kinetic plasma instabilities.

Generate bright gamma rays from the instability.

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PWFA at solid material densities – very strong wakefields

The accelerating field in a wakefield accelerator scales as

Most PWFA/LWFA is done in ionized gas plasma sources at densities much less than atmospheric
Solids are 4-5 orders of magnitude more dense
Drive a wake in a solid density plasma, get 2 orders of magnitude stronger fields than an LWFA

June 19, 2024 R. Ariniello FACET-II Science Overview

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Atmospheric density

Solid density

LWFA

PWFA

Proton PWFA

Solid density wakefield accelerators could produce fields of 10 TV/m.

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Need a solid density nanostructure to provide the electrons

At solid densities, scattering from plasma ions becomes significant

June 19, 2024 R. Ariniello FACET-II Science Overview

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[1]

Acceleration in in a nanostructure provides high density plasma and limits scattering off the solid’s ions.

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Self modulation of the electron beam

Size of the wake scales as

At FACET-II, the driver is much larger than the nanostructures

June 19, 2024 R. Ariniello FACET-II Science Overview

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[1]

Goal is to see evidence of this bunching – lets us know if we understand the physics.

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FACET-II accelerator diagnostics science

Lots of experiments already planned for FACET-II (and more not included here!):

June 19, 2024 R. Ariniello FACET-II Science Overview

42

Proposal No.	Title
E-300	Plasma wakefield acceleration
E-301	Tailored plasma sources for plasma wakefield acceleration
E-308	Extreme focusing with a passive thin plasma lens
E-325	Automatic tuning for PWFA optimization
E-304	Density down ramp injection in PWFA
E-310	Trojan horse injection
E-311	Plasma torch optical density down ramp injection
E-338	Attosecond XUV/X-ray sources driven by PWFA
E-320	Strong field QED
E-332	Near field CTR based focusing of beams – laser-less SFQED
E-305	Beam filamentation and bright gamma ray bursts
E-336	Beam interactions with carbon nanotube materials
E-315	Plasma afterglow attosecond metrology
E-324	Optical visualization of plasma wakefield acceleration
E-326	Non-intercepting beam diagnostics
E-327	Virtual diagnostics for phase space prediction
E-331	Neural network-based tuning

Plasma wakefield acceleration

Strong field quantum electrodynamics

Strong field physics

Accelerator diagnostics

X-ray source application of PWFA

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The FACET-II beam destroys most things placed in it

Lots of standard beam measurements require inserting something into the beam
Difficult anywhere near the electron beam focus

June 19, 2024 R. Ariniello FACET-II Science Overview

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60 µm

New wire scanner card

Wire scanner card halfway through a run

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Afterglow measurement technique

June 19, 2024 R. Ariniello FACET-II Science Overview

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E field barely strong enough to ionize

E field ionizes

Only e- beam

Only laser pulse

e- beam and laser

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Afterglow measurement technique

June 19, 2024 R. Ariniello FACET-II Science Overview

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Measure relative alignment between the laser and the electron beam.

Measure the overlap between the two beams.

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Optical measurements of plasma evolution

June 19, 2024 R. Ariniello FACET-II Science Overview

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Vacuum chamber

Plasma oven

Image plane

M4

~ 0.02 rad

Plasma

column

BP

Δt~0-4ns

λ/2

shutter

reducer

CCD 2

Probe detection setup

>4” objective to capture all scatter light emerging from pipe.

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Optical measurements of plasma evolution

Determines how long one needs to wait to send the next bunch into the plasma – limits repetition rate

June 19, 2024 R. Ariniello FACET-II Science Overview

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0.3 ns

10 µs

Goal: measure evolution of the plasma long after the PWFA electron beams have passed

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Virtual diagnostic for longitudinal phase space prediction

June 19, 2024 R. Ariniello FACET-II Science Overview

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C. Emma and A. Edelen et al.,PRAB 21 112802 (2018)

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Virtual diagnostic for longitudinal phase space prediction

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TCAV measurement

C. Emma and A. Edelen et al.,PRAB 21 112802 (2018)

Use nondestructive measurements to reconstruct a destructive measurement.

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Edge radiation diagnostic

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Single shot non-destructive measurement technique.

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Electro-optic sampling based diagnostic

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Two of them to measure the position of the beam

June 19, 2024 R. Ariniello FACET-II Science Overview

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Summary

FACET-II

High current beams
Multiple bunches for PWFA

Science program

Plasma wakefield acceleration
X-ray light sources
Strong field physics

Strong field quantum electrodynamics
Material interaction
Relativistic plasma instabilities

Accelerator diagnostics

Nondestructive diagnostics

June 19, 2024 R. Ariniello FACET-II Science Overview

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Questions?

What we are trying to do at FACET-II

June 19, 2024

Facility for Advanced Accelerator Experimental Tests

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Fields in the non-linear regime

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Transverse focusing forces are linear in r.

Longitudinal electric field

Transverse focusing field

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Plasma has demonstrated large gradients

June 19, 2024 R. Ariniello FACET-II Science Overview

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I. Blumenfeld, et al. Nature 445 741 (2007)

Gradients of 50 GeV/m have been demonstrated.

6.9 GeV/m

52 GeV/m

47 GeV/m

W.P. Leemans, et al. Nat. Phys. 113 245002 (2014)

M. Litos, et al. Plas. Phys. Cont. Fusion 58 034017 (2016)

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Energy and gradient aren’t the only story, quality matters!

Luminosity

Need:

Lots of charge
Low energy spread
Small emittance
High efficiency

June 19, 2024 R. Ariniello FACET-II Science Overview

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No cares if you can’t make an XFEL/collider out of it!

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Each of these have been demonstrated

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0.13% energy spread

Lindstrom, et al. Phys. Rev. Lett. 126 014801 (2021)

2.75um-rad emittance

Lindstrom, et al. Preprint, (2022)

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Chromatic emittance growth in a plasma

June 19, 2024 R. Ariniello FACET-II Science Overview

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In a nonlinear plasma accelerator, the ion column exerts a linear, radial focusing force on the beam.

Motion in an ion column:

Oscillation frequency depends on particle energy:

Chromatic phase spread causes projected emittance growth for an electron bunch in an ion column.

Emittance growth is minimized when different energy particles overlap in phase space – matched beam.

Emittance growth is a major problem that must be solved in order for plasma-based accelerators to be useful.

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Beam loading

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M. Litos, et al. Nature 515 92 (2014)

Correct beam loading is required for low energy spread.

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Plasma source

June 19, 2024 R. Ariniello FACET-II Science Overview

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Parameter	Requirement
Density
Length
Width
Entrance Ramp
Exit Ramp

Using Gaussian ramps, the entrance ramp length is

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Lots of work to create a good plasma source

June 19, 2024 R. Ariniello FACET-II Science Overview

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Plasma width needs to be at least:

At ,

Lots of work to figure out how to make/optimize the plasma.

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IP area – where the PWFA happens

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Lithium vapor oven

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Laser ionized plasma sources

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Laser ionized plasma sources

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Other things that can be done with PWFA – positrons

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Diagnostics – butterfly technique

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C. A. Lindstrom, 2016 FACET II Science Workshop

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Diagnostics – gamma and x-ray

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0.08 Torr

0.3 Torr

1.5 Torr

GAMMA1

GAMMA2

LFOV

GAMMA1 detector measures intensity�and angular profile

DRZ scintillator or CsI crystal array

GAMMA2 provides spectral info by measuring conversion signal behind filters

Filter set:
DRZ scintillator�immediately sits�behind

Provides information on matching dynamics, trailing bunch offsets, etc

Analysis by P. San Miguel

Slide from Doug Storey