Ultra-High-Intensity Laser-Plasma Interactions: Comparing Experimental Results with Three-Dimensional,Fully-Relativistic, Numerical Simultations

Donald Umstadter

Scott Sepke

Linear opticsX-ray tube

Nonlinear optics (bound electrons)

Chirped-pulse Amplification(1988)

Relativistic nonlinear optics (free electrons)

Laser (1960)

1018

103

11900 2000

Pea

k In

tens

ity (

Wat

ts/c

m2)

20 0/eEr e r

2eeE m c

2peE m c

Mode-locking

Relativistic protons1024

“Moore’s Law” for Peak Laser Intensity

Intense optical laser light can generate radiation across the entire spectrum

Characteristics Femtosecond Tunable Collimated Synchronized Bench-top Bright Micron source

Type THz Infrared X-rays Electrons Positrons Protons Neutrons

Applications• Non-destructive

testing• Radiography• Lithography• Micro-machining• Ultrafast reactions• Metrology

Relativistic self-channeling leads to collimation of the laser beam, which leads to collimation of the electrons.

Beam divergence found to be reduced with increasing laser intensity

Plaser =30 TW

E = 180 MeV

= 1010 e-

laser= 30 fs ~ 0.25o

LANEX

laser= 400 fs = 1°

Laser wakefield plasma waves can accelerate electons to energy 100 MeV in a single millimeter

0t

F ~I

2 / pt l

Emax at t~p

“Monoenergetic” electrons with energy exceeding 150 MeV

•J. Faure et al., Nature 431, 541 (2004) •C.G. R. Geddes et al., Nature 431, 538 (2004)•S.P.D Mangles et al., Nature 431, 535 (2004)

PIC code prediction

experimental result

Particle-in-Cell Laser-Plasma Simulations

An exact field and particle motion solver.

Maxwell’sEquations

Equationof Motion

E,B Fields(, J)

• LSP is a hybrid fluid/particle-in-cell code:¤ Models include plasmas, lasers, ionization, particle beams, QMD equations of state, TE and TM modes…¤ Allows migration between fluid and kinetic solvers.¤ Uses explicit and stable implicit particle and field solvers.

LSP Particle-in-Cell Simulations

256 2.2 GHz Opteron (64-bit) processors128 nodes each containing 4 GB of RAM

PrairieFire Beowulf Cluster•Fully relativistic 1,2,3D Cartesian and cylindrical geometry

•Self-consistent laser-plasma interactions

Plasma wave

30fs laser pulseSelf-injected electrons

Plasma “bubble”

Average Velocity Longitudinal Electric Field

Pea

k P

ower

Rat

e (

PW

-Hz)

1

30-fs pulse duration

3-J energy per pulse

100-TW peak power

10-Hz repetition rate

UNL soon to have a laser with peak power-rate of 1 PW-Hz, highest of any in the US

Diffraction limited laser focusing requires exact-field solutions

• Electron deflection experiment/simulations show that accurate laser fields are essential.

• We have derived exact solutions for arbitrary, focused Gaussian and super-Gaussian laser profiles.

• These models are complex and must be solved numerically.xEzE

yE

xE zEyE

Concluding Remarks

High-intensity laser-plasma interactions (including laser accelerators) is one of few physical systems in plasma physics (which is a many-many-body problem) that can be numerically modeled with reasonable accuracy.

The computing power required for 3-D modeling was reached only in the last decade.

The availability of greater computing power will enable simulations with larger domains and longer durations, which can more accurately model larger interaction regions and higher plasma densities.

The simultaneous rapid increases in laser and computer power are good example of technological convergence.