Rutherford Appleton Laboratory

Three mechanisms interact to cause ion acceleration in PW laser interactions

• Relativistic electrons expelled by the ponderomotive pressure of light wave. To overcome the attractive electric field of the ions, Ee > Ec . The Coloumb energy Ec is approximately

Ec 2 2 ne2lsR

• Later the ions move due to Coloumb repulsion.

Ei 4 2 ne2R2

Rlaser

ls

•Inductive electric field caused by the rapid change in the B field that accelerates ions and decelerates electrons. The energy gained by this process is •

Ei 8 e2n R2

Rutherford Appleton Laboratory

Sophisticated 3D simulations performed by Prof. S.Bulanov and co-workers has revealed that for linear polarisation case

the ion energy is px = 0.61mic

Conclusion: at intensities 31021 Wcm-2, ~1012 protons are accelerated with energies of several hundred MeV

3D computer simulations of ion acceleration process

Rutherford Appleton Laboratory

0.1

10

1000

105

107

109

1013 1015 1017 1019 1021 1023 1025 1027

Tan et al.CR39 resultsCR39 (Dec.98)Recent CR39 resultsLivermore

Ion

ener

gy (

keV

/nuc

leon

)

I2 Wcm-2µm2

Maximum ion energy vs I

PIC simulationS.V.Bulanov et alJETP Lett 71, 407 (2000)

a02 I2

PIC simulationT.Zh.Esirkepov et alJETP Lett 70, 82 (1999)

a0 I2

Prospects for GeV proton acceleration using PW lasers

Rutherford Appleton Laboratory

GeVlacm

cmnE x

e 20318

3

)(10

)(

The energy gain over the interaction length in a plasma wakefield is

When I2 >> 1018 Wcm-2m2, the radiation pressure is so large nearly all electrons are expelled from the photon wave-envelope, generating a “snow-

plough” in which the electron momentum gain is

202

0

20

4

1a

cmn

E

cn

Ep

e

c

ex

cm

eEa

00

00

provided the laser pulse fully interacts with the plasma (i.e. not diffracted)

Accelerating gradients 200 TeV/cm at 1026 Wcm2

Wakefield acceleration

e

cmEc

00

Nd:glass

20 fs seed laser stretched to 400 ps

1000ps

527 nm

3400 J

SHG

LBO1.5 cm

KDP3.8 cm

4452 J

41 %

LBO1.4 cm

KDP1.1 cm

KDP 0.8 cm

3400 J3400 J44 % 46 % 0.2 mJ 4 J

00.20.40.60.8

11.21.41.6

-600 -200 200 600

time (ps)

inte

nsi

ty (

a.u

.) signal out

depleted pump

Output signal and pump intensity profiles

100 PW

Intensity profile after compression

-80 -60 -40 -20 0 20 40 60 80

time (fs)

inte

nsi

ty

FWHM = 22 fs

(0.3 J/cm2)

Rutherford Appleton Laboratory

Ideas for EW lasers (Dr I.N.Ross)

Rutherford Appleton Laboratory

Future Upgrade OptionsGiven Some Technology DevelopmentGiven Some Technology Development

SHG Pump Dielectric Gratings 1μm Output 50cm KDP

F/1 Focusing0.3 EW 1025 W/cm2

THG Pump Dielectric Gratings0.5μm Output 50cm KDP

F/1 Focusing 0.6 EW 1026 W/cm2

Multi OPCPA >1 EW >1026 W/cm2

Rutherford Appleton Laboratory

• The VULCAN PW upgrade is nearly completion - first experiments to university users scheduled November 2002 - laser wakefield accelerator studies

• >100 MeV protons and >1GeV heavy ions expected

• Future upgrades to multi-PW levels are being actively pursued

• The CLF is investigating new designs for average and peak power lasers required for accelerator and fusion applications

Summary