Compact FEL Based on Dielectric Wakefield

Acceleration

J.B. RosenzweigUCLA Dept. of Physics and

Astronomy

Towards a 5th Generation Light Source Celebration of Claudio

PellegriniCatalina Island — October 2, 2010

FELs are Big Science

Size=$

Creating a compact FEL

High brightness beam Very low charge (pC) Attosecond pulse Few 10-8 norm. emittance

High field, short l undulator With HBB, large ,r short Lg

Lowers e- energy needed 2 GeV hard X-ray FEL

Hybrid cryo-undulator: Pr-based, SmCo sheath 9 mm l, up to 2.2 T

FEL w/1 pC driver at 2.1 GeV

J.B. Rosenzweig, et al., Nucl. Instruments Methods A, 593, 39 (2008)

F.H. O’Shea et al, PRSTAB 13, 070702 (2010)

Scaling the accelerator in size Lasers produce copious power (~J, >TW)

Scale in by 4 orders of magnitude challenges in beam dynamics

Reinvent resonant structure using dielectric GV/m fields possible, breakdown limited…

GV/m allows major reduction in size, cost of FEL, LC

To jump to GV/m, mm-THz may be better: Beam dynamics, breakdown scaling Need new power source…

Resonant dielectric laser-excited structure

(with HFSS simulated fields)

New paradigm for high field

acceleration: wakefields

Coherent radiation from bunched, v~c, e- beam Any slow-wave environment Powers exotic schemes: plasma, dielectrics

Resonant or non-resonant (short pulse) operation THz regime easily w/in reach

High average power beams can be produced Tens of MW, beats lasers… good for FEL, LC

Intense beams needed, synergy with many fields X-ray FEL, ICS X-ray source, intense THz

sources

Wakefields in dielectric tube

Schematic of wakefield-based collider

J. Rosenzweig, et al., Nucl. Instrum. Methods A 410 532 (1998). (concept borrowed from W. Gai…)

• Similar to original CLIC scheme • Study for plasma wakefield accelerator

• gg due to charge asymmetry in PWFA• Not a problem for DWA…

• FEL can avoid all this complexity, use one module

The dielectric wakefield accelerator

High accelerating gradients: GV/m level Dielectric based, low loss, short pulse Higher gradients than optical possible Unlike plasma, no charged particles in beam path…

Use wakefield collider schemes CLIC style modular system Afterburner (energy multiplier) possible for existing linacs

Spin-offs High power CCR THz source

€

dU

dz∝ n −1( )kdk ∝∫ kmax

2

€

dU

dz∝ N bkmax

2 ∝ N b /σ z2

Coherent Cerenkov scaling

Cerenkov scaling

Dielectric Wakefield AcceleratorHeuristic View

Electron bunch ( ≈ 1) drives wake in cylindrical dielectric structure Dependent on structure properties Generally multi-mode excitation

Wakefields accelerate trailing bunch

Mode wavelengths (quasi-optical)

€

λn ≈4 b − a( )

nε −1

Peak decelerating field

€

eE z,dec ≈−4Nbremec

2

a8π

ε −1εσ z + a

⎡

⎣ ⎢

⎤

⎦ ⎥

Design Parameters

€

a,b

€

σ z

€

ε

Ez on-axis, OOPIC

*

Extremely good beam needed

€

R =E z,acc

E z,dec

≤ 2

Transformer ratio (unshaped beam)

T-481: Test-beam exploration of breakdown

threshold 1st ultra-short, high charge beams Beyond pioneering work at ANL…

Much shorter pulses, small radial size Higher gradients…

Leverage off E167 PWFA 48 hr FFTB run Excellent beam 3 nC, z ≥ 20 m, 28.5 GeV

Goal: breakdown studies Al-clad fused SiO2 fibers

ID 100/200 m, OD 325 m, L=1 cm

Avalanche v. tunneling ionization studies Prediction: beam can excite Ez ≤12GV/m

T-481 “octopus” chamber

Beam Observations, Analysis

View end of dielectric tube; frames sorted by increasing peak current

Multi-mode excitation – 100 fs, pulses separated by ps— gives better breakdown dynamics?

Breakdown determined by benchmarked OOPIC simulations

Breakdown limit:5.5 GV/m decel. Field(10 GV/m accel.?)

ultrashortbunch

longerbunch

Post mortem images

E169 Collaboration

H. Badakov, M. Berry, I. Blumenfeld, A. Cook, F.-J. Decker, M. Hogan, R. Ischebeck, R. Iverson, A. Kanareykin, N. Kirby, P.

Muggli, J.B. Rosenzweig, R. Siemann, M.C. Thompson, R. Tikhoplav, G. Travish, R. Yoderz, D. Walz

Department of Physics and Astronomy, University of California, Los AngelesStanford Linear Accelerator CenterUniversity of Southern California

Lawrence Livermore National LaboratoryzManhattanville CollegeEuclid TechLabs, LLC

Collaboration spokespersons

UCLA

E169 at FACET: overview

Research GV/m acceleration scheme in DWA Goals

Explore breakdown issues in detail Determine usable field envelope Coherent Cerenkov radiation measurements Varying tube dimensions

Impedance, group velocity dependences Explore alternate materials Explore alternate designs and cladding

Slab structure (permits higher Q, low wakes) Radial and longitudinal periodicity…

Observe acceleration

Awaits FACET construction Reapproval recently submitted Add AWA group to collaboration

Already explored At UCLA, BNL

Bragg fiber

CVD deposited diamond

Slab dielectric structure (like optical)

Observation of THz Coherent Cerenkov

Wakefields @ Neptune

Chicane-compressed (200 mm) 0.3 nC beam Focused with PMQ array to

sr~100 mm (a=250 mm)

Single mode operation Two tubes, different b, THz

frequencies Extremely narrow line width in

THz Higher power, lower width than THz

FEL

Transverse wakes and slab-symmetric structures

Slab symmetric structures: why? Can accelerate more

charge Mitigate transverse

wakes

Transverse wakes at FACET Observable BBU with >10

cm Simulated BBU @ FACET, Initial, 10.7 cm distribution (courtesy AWA group)

4 GV/m simulated wakes for FACET experiment

E-169 at FACET: Acceleration Observe acceleration

10-33 cm tube length

longer bunch, acceleration of tail

“moderate” gradient, 1-3 GV/m

single mode operation

z50-150 m

r< 10 m

Eb25 GeV

Q 3 - 5 nC Phase 3: Accelerated beam quality

Momentum distribution after 33 cm (OOPIC)

Witness beam

Alignment, transverse wakes, BBU

Group velocity & EM exposure

Positrons. Breakdown is different?

FACET beam parameters for E169: acceleration case

Longitudinal E-field

Witness beam, acceleration and BBU

€

t = L /(c − vg )

A High Transformer Scenario using Dielectric

Wakes How to reach high

energy with DWAs? Enhanced transformer

ratio with ramped beam Does this work with

multi-mode DWA? Scenario: 500-1000 MeV

ramped driver; 5-10 GeV X-ray FEL injector in <10 m

Symmetric beam R<2

Ramped beam R>>2

A FACET test for light source scenario

Beam parameters: Q=3 nC,

ramp L=2.5 mm,U=1 GeV Structure: a=100 mm, b=100 mm, e=3.8 Fundamental f=0.74 THz Performance: Ez>GV/m,

R=9-10 (10 GeV beam) Ramp achieved at UCLA.

Possible at ATF, FACET?

Longitudinal wakefields

Longitudinal phase spaceafter 1.3 m DWA (OOPIC)

R. J. England, J. B. Rosenzweig, and G. Travish, PRL 100, 214802 (2008)

Ramped beam using sextupole-correcteddogleg compression

Multipulse operation: control of group velocity

Multiple pulse beam-loaded operation in linear collider Needs low vg

Low Q, e beams shorter, smaller Can even replace large Q

driver

Use periodic DWA structure

in ~p-mode, resonant excitation

Accelerating beam Driving beam Example: SiO2/diamond structure

€

N ×

Standing wave wakes in periodic dielectric

structures

4 pulse train excitation, 2-l separation

Rms pulse length /4,l suppresses HOM

Initial multi-pulse experiment: uniform SiO2

DWA at BNL ATF Exploit Muggli pulse train slicing

technique 400 mm spacing, micro-Q=25 pC, sz=80

mm DWA dimensions: a=100 mm, b=150 mm

BNL multi-pulse experiments

Array of 1 cm tubes Si02, also diamond 325-660 mm l

Large aperture 490 mm case first Use PMQs later…

Operation of pulse train with both chirp signs Sextupole correction

used CTR autocorrelation

4-drive + witness in spectrometer

CTR autocorrelation and FFT

Recent results from BNL multi-pulse experiments

Single, multi- bunch wakes observed

Wakes without mask give fundamental resonant l ~490 mm, per prediction

Resonant wake excitation, CCR spectrum measured Excited with 190 mm

spacing (2nd harmonic) Misalignments yield ~l 300

mm, 1st deflecting mode

1st deflecting mode

Fundamental (@noise level)

2nd harmonic

CCR autocorrelation

Frequency spectrum

Towards GV/m: multiple pulse DWA experiment at

SPARC/X Uses laser comb

technique Bunch periodicity: 190 mm (0.63 ps) 0.5 of BNL case Scaled structure

125 pC/pulse @ 750 MeV

4 pulses + witness 1 GV/m, energy

doubling in <70 cm

>1.1 GV/m wakes in scaled DWA@SPARX

Honey, I shrunk the FEL (not quite yet…CP’s 80th)

FEL itself gets small with small Q, high brightness beams; innovative undulators Lower energy needed Ultimate limit in optical undulators?

Wakefields give very high field DWA gives a credible path Booster for hard X-ray FEL in few m Scaling to low Q synergistic, hard

Expect rapid experimental progress 1st ATF; then FACET, SPARC/X, etc.

TV/m simulated PWFAusing LCLS 20 pC beam