Laser Plasma based accelerators - Institute of...

D Neely 2007 Laser Ion acceleration

Laser Plasma based accelerators

Oxford, July 2009 Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK.

Telephone: (0)1235 821900 Fax: (0)1235 445888 e-mail: [email protected]

David Neely

Central Laser Facility, Oxfordshire

Mayneord-Phillips Summer School 2009:

‘21st Century Radiotherapy:

State-of-the-art and predicting the future’


i. Plasmas as accelerators

ii. Laser drivers

iii. Ion studies

iv. Future developments

Introduction

Ultra-high

Intensity-

“relativistic”


Air breakdown

Astra Laser

In H Atom

Electric field strengths...

1180 -GVcm

Thunderstorm110 -Vcm

130 -KVcm

110 -MVcm

Linacs can support field of ~10’s

MV/cm

before surface breakdown occurs on

the

Real accelerator-

many stages


“PLASMAS GLOW”

generally

The four states of matter

10,000 degrees = 1

eV

Laser

Plasma


A plasma has a resonance frequency for

the collective oscillations of the electrons

about their equilibrium positions

2/1

0

2

÷÷ø

öççè

æ

××

=e

ep

m

ne

ew

2

22

x

tm

xnee

o

e

¶¶

×=××

e

Why study a laser plasma ?

Natural state of matter at high energy densities

A plasma can

respond rapidly

ns to fs timescales

Collective and individual behaviour important - complex

dx

It is the natural tendency

of a system to move

towards equilibrium

During the transition the

most extreme states

possible can be accessed


The effect of a laser field

Force = mass x acceleration

Kinetic energy of the electron averaged

in time over one laser cycle, typically 10’s MeV

Temp = Intensity x wavelength2

Wavelength 800 nm,

Duration 35 fs

cycle every 3.5 fs

+

+++

++++++ +

+++

++++++ +

+++

++++++

electron density

ion density

0

n0

Laser electric field excites plasma wave which

displaced electrons to generate significant

electric fields in a plasma.

Cavitation possible!!


Lasers as ion drivers ?

Intensity = Energy

Lasers can deliver Energy into

very small areas (microns)

in short times (femto seconds)

Photons are uncharged and generally don’t interact much with the air

They are easy to focus

Area x Time

Higher field

Smaller areas

gives larger fields The shorter the pulse

the stronger the field


Making an acceleratorA plasma can support extremely

large accelerating gradients

In a plasma the electrons are already

stripped from the parent ion and the

field which can be supported just

depends on the density

)()/( 35.0 -»= cmne

cmcmVE e

pew

ne = 1018 cm-3

E ~ 10 GV/cm

2

1

2

0

1

0 ))((5.27)( -- = WcmIVcmE

V

Basic accelerator

ne = 1022 cm-3

E ~ 1 TV/cm

At surface of a solid

In gas


n Laser ionises plasma

n Laser excites plasma wave

n Plasma wave can accelerate electrons

+

+++

++++++ +

+++

++++++ +

+++

++++++

electron density

ion density

0

n0

Plasmas as electron accelerators

z

Laser

Gas-Jet

Electron Beam

Plasma


Mangles et al. Phys.Rev. Lett. 2005

Highest energy of laser driven accelerator

using Vulcan “3 mm long”

State of the art for electrons?

S Hooker et al (Oxford)

have recently achieved

mono-energetic GeV

electrons (2007)


i. Plasmas as accelerators

ii. Laser drivers

iii. Ion studies


Introduction


1 EW

1 PW

1 TW

1 GW

1 MW

1 kW

1 W1960 1970 1980 1990 2000 2010

A Brief history of Lasers

Mode-locking (ps)

Q-switching (ns)

Ionisation

Limitation due to non-linear

processes

Aperture Increase (~ns)

Heating ~ KeV

Chirped Pulse Amplification

(CPA) (ps, fs)

Relativistic MeV

OPCPA?


The Vulcan Laser

Vulcan is a

multi-beam Nd:glass

laser system capable of

delivering synchronised beams

to any one of three target areas.

1 shot per hour

Future 10PW by 2014

0

100

200

300

400

500

600

700

800

900

1000

1990 1993 1996 1999 2002


Gemini laser

• Upgrade to 1PW (30 J per shot)

• On-line since 2000 (5 TW)

• Shot every 20 seconds

30 J, 30 fs, 1022 W cm-2

• 20 TW (0.5 J per shot)

StretchAmplify

Compress


Gemini Experimental area

l Commissioning Aug-Sep 2007

l e,g,p and ion beams highly directional

l Synchronous sources

l Semi-automated sample handling May 2008

Future

Diagnostics

area

Radioisotope

handling

area

Changing

roomLead

access

door

R1660

Control

room


Laser matter interactions

Large fusion-class lasers allow us to simulate

these regimes in controlled conditions

Fusion devicesInteriors of stars

WDM Physics: The study of matter at extreme conditions(transient solid density plasmas, non-equilibrium)

Sandia

NIF


Laser summary

• Rapid developments currently worldwide

(10 currently --- 15 PW systems by 2011)

• 10 PW capability 2014

• ELI

• Laser repetition rate limited by flash lamp “waste

heat”

• Diode pumping technology much more efficient

• 5-100 Hz high power capability by 2014


i. Plasmas

ii. Laser drivers

iii. Ion acceleration


Introduction


An ion accelerator

• Laser driven ion acceleration

• Ultra short pulses

• High brightness

Drivelaserbeam

TargetL

t=2L/c

Drivelaserbeam

TargetL

Target Normal

Sheath acceleration

Fields TV/m

Front surface

acceleration

• ps pulses

• 0.1 – 10% efficient

• highly collimated


0

1

2

3

4

5

0.01 0.1 1 10 100

Al foil thickness (microns)

Ma

x p

roto

n e

ner

gy

(M

eV)

0

1

2

3

4

5

0.01 0.1 1 10 100

Al foil thickness (microns)

Ma

x p

roto

n e

ner

gy

(M

eV)

225 mJ @ 106

McKenna 2002

275 mJ @ 5x107

275 mJ @ 1010 contrast

using plasma mirror

Mora fit (130 fs acc time)

Maximum proton energy scaling


Spectral control

-ve moves target

towards parabola

-400um-200um -300um-100um-50umBest focus

-400um -500um -700um-200um -300um-50um -100um -150umBest

focus

-900um

Al 50 nm

CH 200 nm


Proton scaling with laser parameters

Robson et al, Nature Physics 3, 58 (2007)

Laser intensity (W/cm2)

1019 1020 1021

Maxi

mum

pro

ton e

nerg

y (M

eV

)

0

10

20

30

40

50

60

70Fuchs et al Nat Phys 2006

isothermal model


1019 1020 1021

Maxi

mum

pro

ton e

nerg

y (M

eV

)

0

10

20

30

40

50

60


isothermal model

10 micron (1 ps)

25 microns (1ps)

25 micron (various)


1019 1020 1021

Maxi

mum

pro

ton e

nerg

y (M

eV

)

0

10

20

30

40

50

60


isothermal model

10 micron (1 ps)

25 microns (1ps)

25 micron (various)

isothermal model


1019 1020 1021

Maxi

mum

pro

ton e

nerg

y (M

eV

)

0

10

20

30

40

50

60


isothermal model

10 micron (1 ps)

25 microns (1ps)

25 micron (various)

isothermal model

2-phases model

2-phases with 3-D effects

• Scaling study up to ~6´1020 W/cm2

• Isothermal model overestimates energies

• Model revised to include dual temperature

phase; Mora, PRE 72, 056401 (2005)

•Mora PRL 90, 185002 (2003): isothermal

expansion model provides good fit:

• Fuchs et al Nat. Phys. 2, 48 (2006):

• Scaling study up to ~5´1019 W/cm2;

• GEMINI ~6´1021 W/cm2 (one beam)

Model predicts 200 MeV protons


Proton efficiency scaling with laser

parameters

Laser pulse energy (J)

0 100 200 300 400

Con

vers

ion e

ffic

iency

(%

) to

pro

ton

s w

ith e

ne

rgy

gre

ate

r th

an 4

Me

V

0

1

2

3

4

5

6

7

8

10 micron

25 micron

• Conversion efficiency scales linearly

with laser energy

• Maximum measured conversion

efficiency ~6%

Robson et al, Nature Physics 3, 58 (2007)

µ EL


104

105

106

107

105

106

107

108

109

Energy (eV per nucleon)

Ion

s / M

eV

×msr

Ion

s / M

eV

×msr

104

105

106

107

105

106

107

108

109

1010

Energy (eV per nucleon)

Pd3+

Pd10+

Pd17+

Pd23+

O1+

O2+

O5+

a) b)

Pd and O ions observed from heated palladium target;

Typically 70% of total ion energy is carried by Pd ions & 30% by O (and C) ions

Heavy ion acceleration

25 mm palladium target heated to 1000ºC, irradiated at 122J, 2x1020 W/cm2


Ion acceleration

summarysummary• 60 MeV protons

• Up to 10 J per shot of protons

• MeV’s per nucleon for heavier ions

• Can change ion by changing target surface

layer

• Mono-energetic ion observed by many groups

• Simulations good match to data

• 2014--- expect 300MeV protons


i. Plasmas

ii. Laser drivers

iii. Ion studies


Introduction


Need 250 MeV protons

• Hit it harder – generally works.

• New laser……

• Try something new

• Light pressure

"Please, sir, I want some more."

From O Twist, Illustration by George Cruikshank

foto (c) 1997 Fred Espenak


Light Pressure

• At very high intensities a new mechanism can dominate

• The light pressure pushes the whole target forward

• Requires

-“perfect” pulse

-minimum mass target

-very high intensities

• Predicted to have high efficiency

• Predicted to have narrow band energy spectrum

• Many groups investigating at present


New Grants LIBRA (High rep

sources)

• Laser Induced Beams of Radiation for Applications

• Basic Technology Grant, 4 years, £5M, 9-partners

• Oct 2007 start

• High repetition rate (10 Hz)– Protons, ions, g -rays

– Targetry

– Debris

– Diagnostics

• Gemini experiments– Source development

– Beam delivery and control

– Applications


Source development• Control

– Spectral• What is the best method to achieve 250 MeV protons?

• Can we produce sufficiently high energy Carbon beams?

– Energy, direction, purity

• Characterisation– Automated diagnostics

– Characterisation and analysis

• High repetition rate (10 Hz)– 1 Hz “deliverable”

– 10 Hz ideal “gold plated”

– Debris mitigation

• Reliability– Source development

– Beam delivery and control

– Applications


A laser driven accelerator for treatment

Accelerators already exist which can do the job

• Do we want a laser driven ion source?

Only if

• Its cheaper

Laser

driver

1

2

6

5

4

3

•It provides a unique advantage

•Small gantries

•Can synchronise pulse to patient

•Short duration pulses

•Synchronous sources

•Exotic isotopes

Too early to tell, need 2-4 years to spec laser


Conclusion

• Rapid development over 9 years since discovery

• 60 MeV protons

• Expect 200 MeV protons over 5 years

• Many studies for spectral control

• LIBRA grant Oct 2007

• Light pressure

• Medical potential – very early

Laser Plasma based accelerators - Institute of...

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