Plasma Wakefield Energy Doubler for Cornell’s ERL€¦ · Plasma Wakefield Energy Doubler for...

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Plasma Wakefield Energy Doubler for Cornell’s ERL Mike Downer Department of Physics University of Texas at Austin Workshop on "Scientific Potential of High Repetition-Rate, Ultra-short Pulse ERL X-Ray Source" Cornell University June 14, 2006 σ z Goal: σ z ~ λ p as short as possible; σ r σ r << σ z

Transcript of Plasma Wakefield Energy Doubler for Cornell’s ERL€¦ · Plasma Wakefield Energy Doubler for...

Page 1: Plasma Wakefield Energy Doubler for Cornell’s ERL€¦ · Plasma Wakefield Energy Doubler for Cornell’s ERL Mike Downer Department of Physics University of Texas at Austin ...

Plasma Wakefield Energy Doubler for Cornell’s ERL

Mike DownerDepartment of Physics

University of Texas at Austin

Workshop on"Scientific Potential of High Repetition-Rate, Ultra-short Pulse ERL X-Ray Source"

Cornell UniversityJune 14, 2006

σz

Goal: σz ~ λp as short as possible;

σr

σr << σz

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3.2 km

Ebreakdown ~ 107V/m30 GeV ⇒ 3 km (SLAC)

Conventional RF acceleration: limited by material breakdown

Plasma acceleration:unlimited by material breakdown

Eaccel ~ 1011 V/m30 Gev ⇒ 0.3 m

1 mm

≤ 1 GeVelectrons

laser pulseor electron bunch

plasma wavene

ne0

z

picture courtesy D. Umstadter

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100

1000

40 50 60 708090100 200 300Energy (MeV)

∞200100082605_#94

Quasi-monoenergetic (Emax=160 MeV*)...

±15 MeV

laser

e- beam

gas

B

phosphor screen

Q ~ 1 nC

15 mm Pbphosphor

screen

E > 70 MeV e-

... & highly collimated(σ⊥ = 0.1 π mm-mrad)beam can be produced

convertible to 10 fsx-ray pulse

~10 fs bunch duration

*Faure et al., Mangles et al, Nature (2004)recent results: Emax = 300 MeV (Michigan)

1 GeV (UC-Berkeley)

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Emerging small-scale applications of LASER-plasma accelerators (0.1 - 1 GeV)

Chemistry& Nutrition

Radiolysis;

Electrons &Protons fromLaser-PlasmaAccelerators

Fs-time resolved x-ray & electron

diffraction

Flash γ-ray radiographyof stressed materials

NuclearMedicine

Proton Cancer therapy; 11C production for PET

NuclearEngineering

Rare, short-lived isotopes; Transmutation of nuclear

waste MaterialsScience

StructuralBiology & Chemistry

Food sterilization

(U. Pittsburgh)

HIGH ENERGYPHYSICS

or energy doublerplasma “afterburner”,

Particle-beam-driven plasma accelerators

fill a unique niche

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Positron beam

Electron beam

Electron gun200-MeV injector

Positron source

Positron return line

Particledetector

50-GeVpositrons

50-GeVelectrons

Plasma Plasma lens

20 meters

3 kilometers

Main linearaccelerator

PLASMA AFTERBURNERS

Demonstrated to date (E-157,162,164, 164x):• 27 GeV electron, 1 GeV positron

energy gain in 0.1 m plasma• > 2-fold improved focus

Chandrasekhar Joshi, Scientific American (Feb 2006)

Goal: double beam energy of conventional collider

SLAC / UCLA / USC collaboration

“Plasma Afterburner”: Booster for conventional accelerators Lee, Katsouleas et al., “Energy doubler for a linear collider,” Phys. Rev. ST-AB 5, 011001 (2002)

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The largest accelerating gradients are realized in the densestplasmas, using the shortest drive bunches

(eE)linear = 240 MeV

mN

4 ×1010⎛ ⎝ ⎜

⎞ ⎠ ⎟

0.6σ z [mm]

⎝ ⎜

⎠ ⎟

2

For optimized kpσ z ≡ 2 :

3D PIC simulations show the dependence predicted by linear theory (nb < n0)persists into nonlinear regime (nb > n0)

σ z−2

Lee, Katsouleas et al., Phys. Rev. ST-AB 5, 011001 (2002)

bunch length

σz

kp-1

N = 4 × 1010

E-157(20 ps)

E-164X(~70 fs)

Cornell ERL(20 - 50 fs)

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For optimized bunch length best PWFA is realizedin the nonlinear “blowout” regime: nb >> n0 AND kpσr < 1

kpσ z = 2,

Rosenzweig et al., Phys. Rev. A 44, R6189 (1991)Hemker et al., Phys. Rev. ST-AB 3, 061301 (2000)

Wz [GeV/m]

0.0

drive bunch

drivebunch

kpr

kpξ

∂Wz /∂r = 0

0.5

1.0

• linear focusing force,

∂Wr /∂z = 0

independent of z

⇒ drive pulse & trailing accelerating bunch propagate stably, w/ low emittance growth

acceleratingbunch

• uniform accelerating field profileDesirable properties:

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Cornell ERL can pick up where SLAC left offExpt. τbunch

[fs]σz

[µm]σr

[µm]noptimum

[1018 cm-3]Ez

max

[GeV/cm]Lplasma

[cm]∆E

[GeV]

SLACE-157

2000 600 ~50 0.00016 0.0024 100 0.24SLACE-164X 70 20 ~20 0.14 0.5 3-30 1-15Cornell

Short-Pulse

50 15 < 5 0.25 1.0 1-5 1-5CornellUltra-Short

Pulse20 6 < 2 1.56 5 ~1 5

• E-157: long bunch, σr/σz << 1, low density, low gradient

• E-164X: short bunch, σr/σz ≈ 1, medium density, high gradient

• Cornell: ultrashort bunch, σr/σz << 1, high density, ultrahigh gradient

THEORY SPARSE ⇒ EXPERIMENTS NEEDED

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First Generation Experiment: to perfect plasma wakes, we must SEE them

• Generate wakefields in dense plasma (~ 1018 cm-3) using ultrashort, low emittance ERL bunches

• Measure wake structure by Frequency Domain Holography,using ~ mJ probe laser pulses synchronized w/ photocathode laser

• Compare FDH measurements with (PIC) simulations

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Copper RF acceleratorcavities must be

precision-engineered

Simulations show widely vary-ing plasma wake structures...

...AND we can’t even see them!

Driving Pulse

Electron density

Sinusoidal

~50 µm

Distorted sinusoid

Spherical “bubble”

Electron densityDriving Pulse

Distorted sinusoid

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Wakefield ne = n0 + δne(t) IonizationFront

ChirpedReferencePulse (400nm)

ChirpedProbePulse (400nm)

Ultra-intense Pump Pulse, 1Joule, 30 fs, 800nmor Electron Bunch, 1 nC, 20-50 fs

Single-Shot “Frequency Domain Holography”

Chirped Probe is temporally long and records effect of multiple oscillations simultaneously, meaning technique is single-shot

Fixed Delay, Δt

CC

D

grating

imagingoptics

mirror

imaging spectrometer

Null HOLOGRAM

Signal HOLOGRAM

Wavelength [nm]

50

-50

0

50

-50

0

dist

ance

[μm

]

390 400 410405395

NicholasMatlis

Ph.D.’06

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RECONSTRUCTION

“Reading” the Hologram

Εprobe(ω) = |Ε(ω)| e-iφ(ω)

(Full Electric Field Reconstruction)

BASIC SCHEME

1. Reconstruct spectral E-field of probe pulse from holographic spectrum

Hologram

388 390 392 394 396 398 400 402 404 406 408 410

Eprobe(t) = |E(t)| e-iδφ(t)

2. Fourier Transform to the time-domain to recover temporal phase

Εprobe(ω)FFT

Read

δφ(t)

3. Calculate electron density from extracted temporal phase

δne(t)index

Wakefield

TIME DOMAIN

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r (µm)-500

500t (fs)

He2+

He+

• Ipump= 1016 W/cm2

• single shot measurement

Holographic snapshot of an ionization frontLeBlanc, Matlis, MD, Optics Letters 25, 764 (2000)

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0 -200 -400200400600

0

50

100

-50

-100

Time [fs]

Rad

ial D

ista

nce

[μm

]

a)

Wake Oscillations

Ionization Front

Pump propagation

ne = 0.95 x 1018 cm-3

0 -200 -400200400600

0

50

100

-50

-100

Time [fs]

Rad

ial D

ista

nce

[μm

]

b)ne = 0.95 x 1018 cm-3

He2+ He+

PIC simulation (11 TW pump)

0 -200 -400200400600

0

50

100

-50

-100

Time [fs]

Rad

ial D

ista

nce

[μm

]

c)ne = 5.9 x 1018 cm-3

6e184e182e180e18

80

100

120

60

40

Electron Density [cm-3]

Pla

sma

Per

iod

[fs]

140d)

Holographic snapshots of laser wakefieldsP ~10 TW, I ~ 1018 W/cm2

Ezmax ~ 3x1010 V/m

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0

60

120

-60

-120

Time [fs]

Rad

ial D

ista

nce

[μm

]

a)

200 0 -200400600800

ne = 2.17 x 1018 cm-3

Strong wakes have curved wavefrontsP ~30 TW, I ~ 3 x 1018 W/cm2

0

60

120

-60

-120

Time [fs]

Rad

ial D

ista

nce

[μm

] a)

200 0 -200400600800

ne = 2.17 x 1018 cm-3

n e[1

018cm

-3]

0

1.0

2.0

3.0

4.0

0

60

120

-60

-120

Rad

ial D

ista

nce

[μm

] b)

200 0 -200400600800

PIC simulation (40 TW pump)

Time [fs]

γ ≈ 1

ωp = [nee2/ε0γ me ]1/2

γ ≈ 1.5

a)

background plasma subtracted

Importance of wavefront curvature:

• collimates e- beam• threshold of wave-breaking

& electron injection• Ez

max ≈ 1.5 x 1011 V/m

N. H. Matlis et al., submitted to Nature Physics (2006)

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PWF-accelerated beam properties to measure• energy • transverse emittance • bunch length• energy spread • bunch charge

Plasma wake physics to observe by FDH

• PWF microstructure vs. drive parameters (σz/σr, N) in the high density blowout regime, where theory is sparse and simulations problematic.

• Effect of beam loading & drive bunch depletion on wake structure

• Onset of wave breaking & electron injection from background plasma

• Onset of hosing instability...

Characterize x-rays emitted by...

• Betatron oscillations in ion column• Thomson scatter by counter-propagating intense laser pulse

• Re-injection into ERL undulators[e.g. 107 photons @ 6.4 keV in .01o cone]1

1 SLAC E-157 2 T Phuoc, PRL 90, 075002 (2003), laser wakefield

[108 photons@ 1keV]2

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Summary• Plasma wakefield boosters can potentially add flexibility

to the Cornell ERL at low cost- optional increased energy- auxiliary ultrashort hard x-ray source

• R&D using visualization methods such as FrequencyDomain Holography, is needed to perfect them

• They may also provide low-cost upgrades for HEP accelerators

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Characteristic SLAC E-164X Cornell ERL Importance

τbunch ~70 fs 20-50 fsresonantly drive WF in dense (ne > 1017 cm-3) plasma ⇒ high accelerating gradient (Ez > 100 GeV/m)

transverse emittance

60 ×15mm-mrad

5 mm-mrad tight focusσr < λp ~ 10 µm

bunch charge ~ 5 nC ~ 1 nC nbunch > ne

repetition rate 10 Hz ~ MHz

• high S/N in physics experiments• high average current from plasma WF

accelerator

“blowout” regime:• stable propagation• low emittance growth• optimum Ez

The Cornell ERL is well qualified for 2nd generationplasma afterburner accelerator experiments

• basic physics• accelerator development

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Counter-propagating Thomson scatter:tunable, fs X-ray pulses on a table-top

CounterCounter--propagating Thomson scatter:propagating Thomson scatter:tunable, tunable, fsfs XX--ray pulses on a tableray pulses on a table--toptop

Undulatorsynchrotron

e- beam(GeV)

X-ray beam:λ= λund/2γ2

cm

Counter-propagatingLaser LWFA

e- beam(~tens MeV)

μm

X-ray beam:λ= λL/4γ2

Banerjee et al., Phys. Plasmas (2002)Ta Phuoc et al., PRL 90, 075002 (2003)