Progress of Novel Vacuum Laser Acceleration Experiment at ATF

Xiaoping Ding, Lei ShaoATF Users’ Meeting, Apr. 4-6, 2007

Collaborators:• D. Cline (PI), X. Ding, and L. Shao UCLA, USA• Y.K. Ho (Co-PI), Q. Kong, and J. Xu Fudan University, China• I. Pogorelsky, V. Yakimenko, and K. Kusche BNL, USA

Approval letter for novel VLA experiment at ATF

Outline

Review of Theory behind Experiment.

Capture and Acceleration Scenario (CAS) Scheme.

Simulations Based on Possible ATF Experimental Conditions.

Experimental Setup and Plans.

Review of Theory behind Experiment

• Lawson-Woodward theorem: in the plane wave V >c, the electrons may experience the acceleration and deceleration phases alternately. Net energy gain is zero.

• Ponderomotive scattering in a non-focused laser: electrons are accelerated in the front of pulse, and decelerated in the tail of pulse. The net energy gain is nearly zero.

• Ponderomotive scattering in a tightly focused laser: electrons may obtain a larger energy near the focal point, and lose less energy at the deceleration phase (diffraction effects break the symmetry of acceleration and deceleration process). But the energy gain is limited.

• Novel VLA (CAS scheme): the diffraction not only changes the intensity distribution of the laser, but also its phase distribution, which results in V <c in some areas. Thus, in some special regions, which overlaps features of both strong longitudinal electric field and low laser phase velocity, electrons can receive high energy gain from the laser.

Schematic electron beam trajectory

Capture and Acceleration Scenario (CAS) Scheme

Contour of phase velocity in a tightly focused laser (Gaussian beam)

Quality factor and Acceleration Channel

Required Parameters for CAS to emerge

• E-beam energy routinely varies from 40 MeV to 70 MeV

• 20 MeV electron beam at 200pC has been successfully tuned to the end of Beam Line 1 (BL1) by Feng Zhou with normalized transverse emittance below 3.5 μm and energy spread smaller than 0.15%.

• The availability of 10 MeV e-beam is under study.

• 10.6 μm CO2 laser with 5J and 5ps, 1TW level is available; 3TW will come soon

• Higher resolution and wider energy acceptance energy spectrometers with 900 and 40 dipoles, respectively.

Simulations Based on Possible ATF Experimental Conditions

-6000 -4000 -2000 0 2000 4000 6000 8000 10000 12000

-1000

0

1000

-6000 -4000 -2000 0 2000 4000 6000 8000 10000 12000

101520253035

0 50000 100000 150000

-50

0

50

100

150

200

250

300

350

400

-400 0 400

1.00

1.01

1.02

W(z)

W(z)

x(1/

k)

(b)

(a)

~(30-20)*0.511MeV=5.11MeV

E(0

.511

MeV

)

-6000 -4000 -2000 0 2000 4000 6000 8000 10000 12000

1.00

1.01

1.02 (d)

V(electron)

V(phase)

Ve

& V

phas

e

z (1/k)

-6000 -4000 -2000 0 2000 4000 6000 8000 10000 12000

0100200300400

(c)

Lase

r P

hase

(de

gree

)Simulation of Electron Dynamics

Parameters for Simulation:

Electron-beam: 10MeV

Laser Intensity: 3TW, 20 waist size, 10.6 wave length .

Laser description:

)(2

)()(exp

)(exp

)(

22

02

220

0 zk

yxkzkzti

zw

yx

zw

wEEx

2

1

220

0 )2

(1)(

kw

zwzw

2

20 )

2(1)(

z

kwzzR

)2

(tan)(20

1

kw

zz

m m )5( 0 a

As we can see, the simulation clearly demonstrates that electrons can get energy gain from laser beam after the entire interaction. Under the parameters we used above, the electron can be accelerated of the gradient about 5MeV/1.7mm.

Vm

Distribution of Phase Velocity on y=0 plane

-4000 -2000 0 2000 4000 6000

-0.016

-0.012

-0.008

-0.004

0.000

0.004-4000 -2000 0 2000 4000 6000

-0.5-0.4-0.3-0.2-0.10.00.10.20.30.40.5

Fx (

tota

l)

z (1/k)

Fx(B)=-Vz*By*(-e)

Fx(E)=Ex*(-e)

Fx (

E &

B)

-3000 -2000 -1000 0 1000 2000 3000 4000 5000-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04-3000 -2000 -1000 0 1000 2000 3000 4000 5000

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

Fz (

tota

l)

z (1/k)

Fz(B)=-Vx*By*(-e)

Fz(E)=Ez*(-e)

Fz (

E &

B)

Transverse and Longitudinal E&M force performance during Interaction

Basically, according to the simulation work, this new vacuum laser acceleration scheme could have a chance to be carried out in a real experiment under the promising ATF experimental conditions, which are expected in the near future.

By then it would turn out a revolution of a new acceleration concept, which gives acceleration gradients as high as GeV/m in vacuum laser acceleration without any optics.

10-MeV e-beam study

Parmela shows 10 MeV electron beam at 200pC with energy spread below 0.1% can be obtained at the end of Linac

Experimental Setup and Plans

• Plans To demonstrate novel VLA - Continue efforts to tune e-beam at lower energy, such

as 10-MeV - Adjust laser optics to produce incident laser injection

to e-beam - Measure angular distribution and energy gain In addition to our leading this experiment at ATF,

Prof. Ho from Fudan University is also leading a similar experiment in China by using SILEX-I Laser Facility (Ti-Sapphire, 286TW,30-fs laser ) and we will help the experiment.

SILEX-I: SILEX-I: SSuper uper IIntensity ntensity LLaser for aser for EExtreme Extreme ExxperimentsperimentsGeneration of 286-TW, 30-fs Laser Pulses Generation of 286-TW, 30-fs Laser Pulses

SILEX-ISILEX-I Laser Facility

SILEX-I:SILEX-I: 286TW-stage286TW-stage

80mm Ti:sapphire slab with cladding80mm Ti:sapphire slab with cladding• Beam diameter 60mmBeam diameter 60mm• Four-pass amplifierFour-pass amplifier• Pumping: 90-J, 8-ns pulse green lightPumping: 90-J, 8-ns pulse green light(for 286TW, only 50J needed)(for 286TW, only 50J needed)• Four-grating single-pass compressorFour-grating single-pass compressor

•High gain coefficient laser medium•ASE-physical issue for large aperture rod•High refractive index 1.76•Index-matched thermoplastic material for cladding

Pump Laser:Energy:150J/1064nm, 80~90J/532nm

Beam diameter: 64mm

Pulse duration: 8ns

Thanks a lot!