Application of Plasma Waveguides to Advanced High Energy Accelerators

H.M. Milchberg+* and T.M. Antonsen, Jr.#*

*Institute for Physical Science and Technology#Institute for Research in Electronics and Applied Physics

*Departments of Electrical Engineering and PhysicsUniversity of Maryland, College Park, MD 20742

*Supported by USDOE

DEFG0297ER41039

Scientific Goal

• To develop the basic science and technology of intense laser pulse propagation in plasma waveguides for laser-plasma based accelerators

Experiment: plasma channel formation, laser pulse propagation and coupling, novel plasma media (cluster gases), advanced diagnostics

Theory: nonlinear pulse propagation, advanced computational models and algorithms, laser - cluster interactions

Success: stable propagation of intense(I ~ 1018 W/cm2) guided laser pulses for 10s of cm.

Major Accomplishments

• Conceived and developed hydrodynamically formed plasma channels; characterized channels and pulse propagation

• Developed Single Shot Supercontinuum Spectral Interferometry (SSSI)

• Discovered and characterized self-focusing in cluster gases

• Delineated competition between self-focusing and Raman scattering for intense laser pulses

• Developed quasistatic particle modeling of plasma wakes

University of Maryland Channel Formation Scheme

axicon

nozzle

waveguide generationpulse

1064nm,200-300 mJ, 100ps

gas flow

gas feed from10Hz pulsed valve at ~30 atm

axicon line focusand plasma waveguide

injectedpulse

800nm20-80 mJ

100 fs

45 deg. mirror with hole

dx

Generation of a plasma waveguide in an elongated, high repetition rate gas jetJ. Fan, T.R. Clark, and H.M. Milchberg, Appl. Phys. Lett. 73, 3064 (1998)

Use of Axicon to Generate Plasma Channel

axicon (conical lens)

plasma channel

moderate intensityfibre generating pulse:100-500 mJ, 1.064 um100 ps

hole for guided pulse

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30k

⊥r

( )E r

r

z

J0(kr)

Channel MeasurementTime-and space-resolved density evolution of the plasma waveguideT.R. Clark and H.M. Milchberg, Phys. Rev. Lett. 78, 2373 (1997).

General layout of experimental set-up

200 torr N2O at delays of 70ps, and 1, 6, and 10 ns

Radial density profiles extracted using Abel

Inversion of phase data for 150 torr Kr

Density inversion required for guiding

cutoff condition

ΔNp m

r re

e m

>+ +( )2 1 2

2π

parabolic waveguide

r

Ne rm

TR Clark et al, PRE 61, 1954 (2000)

ring: p=0, m<6central spot: numerous p>0, m=0

skewed coupling selects azimuthal modes

Plasma waveguide mode structure

p = radial indexm = azimuthal index

20

2

)/(1

)(

ww

wkm

ch

chopt +

=θ

p=0 m=0

m=0 m=3

multimode

θ

Probed with weak diverging beam

Frequency shifts are given by

= =

where L : Interaction length : Laser wavelength n : Refractive index

Nc : Number of clusters per cm3

and : Ensemble averaged cluster polarizability

Spectral redshifts ( < 0) are expected when the real part of cluster polarizability increases with time at the early stage of interaction.

† Polarizability :

Gas jet nozzle

t (ps)

× 10-16 cm3

r (m)

)ãRe( (+) n() n

Laser pulse

I(r)

r

Clusters

† K. Y. Kim et al., Phys. Rev. Lett. 90, 023401 (2003).* I. Alexeev et al., Phys. Rev. Lett. 90, 103402 (2003).

)(t [ ])(2 1 tnL dtd−− λπ [ ])(4 12 tLN dt

dc γλπ −−

Self-focusing and frequency shifts

In cluster gases

γπγπ cc NNn 21)41( 2/1 +≈+=

γ

Self-focusing *

single shotsupercontinuumspectral interferometry

transient guiding profile

(nr-1) x10-4

ni x10-4

Advanced Diagnostics

PRL(2003)

Self-focusing of intense laser pulses in clustered gases

1.4 ps

600 fs

150 fs

350 fs

VF

SF

600

m

80 fs

2.8 mm

VF

80 fs

beam

I. Alexeev, T.M. Antonsen K.Y. Kim and H.M. Milchberg PHYS REV LETT 90 (10): Art. No. 103402 MAR 14 2003

Focusing varies with pulse length due to time dependence of polarizability

Side imaging

End Imaging

Guiding of Intense Laser Pulses in Plasma Waveguides Produced from Efficient,

Femtosecond End-Pumped Heating of Clustered Gases (PRL2005)

Experimental layout

Extracted electron density profile

Imaged guided mode

Plasma waveguides efficiently generated by long-pulse Bessel beams in elongated cluster gas jets

PRE (2005)

clustered gas jet

screen cooling blockplasma

Bessel beam profile after line focus

axicon

PIC simulations of cluster heating(PRL 2004)

0.0001

0.001

0.01

0.1

0 2 1012

4 1012

6 1012

8 1012

1 1013

14.2 nm26.1 nm38.0 nm38.0 nm, Z=453.4 nm38.0 nm, GI38.0 nm, 3D

Intensity/D0

2 [(W/cm

2)/nm

2]

y=0

Energy absorbed vs Intensity

Phase space (x - vx) for electrons y=0

Modeling Propagation of Ultra-Intense Laser Pulses

Accomplishments• Developed first quasi-static laser-

plasma particle code (WAKE-2D PoP 1997)-raman instability-self-focusing-wakefield generation-test particle acceleration-ionization

• Extended to 3D with UCLA group(QuickPIC, JCP 2006)

-beam driver-wake loading

• Planned: plasma pick-up

Simulation of Ionization Scattering Instability

Laser Pulse

Funding

Current: DoE-HEP $245k NSF-DoE Plasma $250k

Cumulative: DoE-HEP 1997-2006: $2.0M NSF-DoE 1997-2006: $2.2M

Staff FY05: 2 faculty, 1 postdoc (left 6/05), 7 Ph.D. students

Ph.D.s: (9) Z. Bian, J Wu, J. Cooley, T.R. Clark, S. P. Nikitin, I. Alexeev, J. Fan, E. Parra, K.Y. Kim

Highlights

Honors and Awards1999 American Physical Society Doctoral Dissertation Award in Plasma Physics (Tom Clark)2004 American Physical Society Doctoral Dissertation Award in Plasma Physics (Kiyong Kim) 2003 IEEE Plasma Science Applications Award (Antonsen)2004 A. James Clark Outstanding Faculty Research Award (Antonsen)2005 University of Maryland Distinguished Scholar-Teacher Award (Milchberg)2005 APS Award for Excellence in Plasma Physics Research (Milchberg)

New laser facility (IREAP)20 Terawatt Ti:Sapphire laser (10 Hz, 600 mJ, 30 femtosecond pulse), capable of >1020 W/cm2

Funding: DoE supplemental budget request for $300k UMD commitment $503k

We are seeking to add a new faculty position

Program Review/Community Feedback

• Starting (5/06) 4th 3-year grant

• Current renewal proposal is under review

• Previous 3 proposals reviewed by ~3 anonymous reviewers, comments forwarded to us for consideration/action

• 3 site visits by DoE-HEP personnel

• Advanced Accelerator Concepts Workshops

Computation working group

Guiding working group

Experimental verification of resonance absorption of Bessel beams in

plasma waveguide formation

pump axiconbeam splitter

energy meter

plasma channel

for side-coupledmode imaging

350 mJ, 100ps1064 nm

Experimental Set-Up