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ICF-related research at Strathclyde Paul McKenna University of Strathclyde
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ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Dec 21, 2015

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Page 1: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

ICF-related research at Strathclyde

Paul McKenna

University of Strathclyde

Page 2: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

EPSRC grant: EP/E048668/1 Key physics for ICF diagnosed by ion emission

1. Fast electron generation and transport in dense plasma

2. Shock propagation physics

3. Laser-ion source development (ion fast ignition)

• (Nuclear diagnostics of laser-plasma)

Page 3: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Fast electron generation and transport:

Diagnostic Energy range

Issues

K emission 10s keV Wavelength shift with temperature

CTR / OTR emission

MeV Limited to thin targets due to electron bunch dephasing

“Escaped” electron spectrometry

MeV Target charges to MV potentials

Notoriously difficult to measure fast electrons in solid targets. Each diagnostic has limitations due to assumptions, model dependences etc.

Examples:

Page 4: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Our approach: Ion emission as a diagnostic

Laser pulse

Target RCF stack Sample RCF

Beam sampling for analysis

Protons

Structured sheath

• Maximum proton energy electron density (MeV energies)• Intensity distribution electron transport filamentation• Proton divergence with energy electron sheath profile • Proton spectrum electron temperature (model)

• Thick solid density targets can be investigated (>mm)

Page 5: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

0 100 20015

20

25

30

35

40

Scale length, LO

(m)

Ma

xim

um

pro

ton

en

erg

y (

Me

V)

0 100 2000

1

2

3

4

5

6

7

Scale length, LO

(m)

En

erg

y c

on

ve

rsio

n e

ffic

ien

cy (

%)

Iabl

t

0 100 20015

20

25

30

35

40

Scale length, LO

(m)

Ma

xim

um

pro

ton

en

erg

y (

Me

V)

0 100 2000

1

2

3

4

5

6

7

Scale length, LO

(m)

En

erg

y c

on

ve

rsio

n e

ffic

ien

cy (

%)

0 100 20015

20

25

30

35

40

Scale length, LO

(m)

Ma

xim

um

pro

ton

en

erg

y (

Me

V)

0 100 2000

1

2

3

4

5

6

7

Scale length, LO

(m)

En

erg

y c

on

ve

rsio

n e

ffic

ien

cy (

%)

Iabl

t

0 100 20015

20

25

30

35

40

Scale length, LO

(m)M

axim

um

pro

ton

en

erg

y (

Me

V)

0 100 2000

1

2

3

4

5

6

7

Scale length, LO

(m)

En

erg

y c

on

ve

rsio

n e

ffic

ien

cy (

%)

0 100 20015

20

25

30

35

40

Scale length, LO

(m)

Ma

xim

um

pro

ton

en

erg

y (

Me

V)

0 100 2000

1

2

3

4

5

6

7

Scale length, LO

(m)

En

erg

y c

on

ve

rsio

n e

ffic

ien

cy (

%)

1011

1012

1013

0

5

10

15

20

25

30

35

40

Intensity (W/cm2)

Shock f

ront po

sition (u

m)

Cu 0.5 ns

Cu 1.5 ns

Cu 3.5 nsAu 0.5 ns

Au 1.5 ns

Au 3.5 ns

-60 -40 -20 0 2010

-4

10-3

10-2

10-1

100

101

102

X-position (microns)

Densi

ty (g/c

m3)

0.5 ns

1.5 ns3.5 ns

1011

1012

1013

0

5

10

15

20

25

30

35

40

Intensity (W/cm2)

Shock f

ront po

sition (u

m)

Cu 0.5 ns

Cu 1.5 ns

Cu 3.5 nsAu 0.5 ns

Au 1.5 ns

Au 3.5 ns

-60 -40 -20 0 2010

-4

10-3

10-2

10-1

100

101

102

X-position (microns)

Densi

ty (g/c

m3)

0.5 ns

1.5 ns3.5 ns

Proton measurements show that controlled preplasma expansion leads to enhanced energy coupling to fast electrons

1: Laser propagation and energy absorptionP. McKenna et al, LPB 26 591-596 (2008) D.C. Carroll et al, CRP 10 188-196 (2009)

Page 6: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

OSIRIS Simulations

-200 -100 0

1018

1020

1022

1024

X (m)

Ele

ctro

n d

en

sity

(cm

-3)

-10 0 10 2010

23

1024

1025

X (m)

n e (cm

-3)

Pollux 0.5 nsPollux 3.5 nsExpt. 0.5 nsExpt. 3.6 ns

• Preplasma expansion enhances electron energy spectrum

• Self focusing and beam break-up observed

• changes to the electron injection angle

0 20 4010

3

104

105

Electron energy (MeV)

Num

ber

of e

lect

ron

(arb

. uni

ts) Sharp gradient

Pollux 0.5 nsPollux 3.5 ns

Sharp density gradient

0.5ns Pollux density profile

3.5ns Pollux density profile

Simulations by Roger Evans

Page 7: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Evidence of collimation of fast electrons in solid targets by self-generated B-field observed using proton emission

2. Collimation of fast electron transport

Yuan…McKenna., submitted (2009)

0 300 600 900 1200 15000

10

20

30

40

Target thickness (m)

Max

imum

pro

ton

ener

gy (

Me

V)

ballistic model (27o) RCFTP-Spec

0 300 600 900 12000

100

200

300

400

500

Target thickness (m)

Sh

ea

th d

iam

ete

r (

m)

ballistic model (27o)Inferred from expt.

Page 8: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Simulations with 2-D hybrid LEDA code

Electron refluxing within thin targets perturbs B-field structure

Ne no B field Ne with B field

Simulations by Alex Robinson (RAL)

Page 9: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

3: Effects of target material on beam filamentation

CH SiO2 glassBk7 glass

Li Al Au

Laser pulse

Target RCF stack

Sample RCF

Protons

Target Effective Z Resistivity[Ω.m]

Al 13 10-8

C3H6 5.4 1013

Li 3 10-7

SiO2 11.6 1014

Page 10: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

ZEPHROS hybrid-PIC simulationsSimulations by Alex Robinson (RAL);

Li curve calculation by Mike Desjarlais (Sandia)

Page 11: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

4. Shock propagation physics• Exception sphericity of implosion required for ICF

• Non-uniformities in illumination or target roughness amplified by Richtmeyer-Meshkov and Rayleigh-Taylor instabilities

• Uniform drive pressure can result in non-uniform shock propagation depending on grain alignment in the material

• e.g. Be is naturally polycrystalline with different shock velocities along different crystal axes – grain size is ~10 m

D Swift et al.,

Page 12: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Shock uniformity measurements using proton emission

Our approach – use proton emission imaging to measure perturbations of the initial shock breakout

CPA illumination timed to coincide with shock breakout thus imprinting the rear surface geometry on the ion emission.

Proof-of-principle tests in January 2010

Sub-micron structure on target surface

Reproduced in proton beam

M. Roth et al., PR-STAB 5, 061301 (2002)

Lindau et al., PRL 95, 175002 (2005)

Proton emission is sensitive to shock breakout

Page 13: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Laser pulse energy (J)0 100 200 300 400

Con

vers

ion

effic

ienc

y (%

) to

pro

tons

w

ith e

nerg

y gr

eate

r th

an 4

MeV

0

1

2

3

4

5

6

7

8

10 micron25 micron

Robson et al, Nat Phys 2007

EL

10 µm Al, ~5 µm

25 µm Al, ~5 µmControlling the front surface density

gradient gives a factor of 2 increase in conversion efficiency

2 µm Al, ~80 µm, ~1019 Wcm-2

Thin targets and defocused laser spot gives even higher conversion efficiency

• DT fuel at 300g/cc• 35 m ignition spot

Curved proton rich target

5: Laser-ion source development

• Proton energy scaling with ps pulse

• Spectral shaping with dual CPA pulses

• Techniques to enhance conversion efficiency

Page 14: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

1. Proton emission applied as a diagnostic of fast electron generation and transport

Examples:

• Electron generation as a function of plasma scale length

• Collimating effect of self-generated magnetic fields

• Electron transport filamentation

• Electron transport in compressed targets (HiPER, LULI)

2. Shock propagation physics

• Ion diagnostic technique to be trialled in January 2010

3. Laser-ion source development (ion fast ignition)

• Spectral control and enhancement of conversion efficiency

4. Nuclear diagnostics of laser-plasmas

Summary of ICF-related physics at Strathclyde

Page 15: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Collaboration:

P. McKenna et alSUPA, Department of Physics, University of Strathclyde

D. Neely, A.P.L. Robinson et al STFC, Rutherford Appleton Laboratory

R G Evans Imperial College London

M. Borghesi, M. Zepf et al School of Mathematics and Physics, Queen’s University Belfast.

J. Fuchs et al LULI Ecole Polytechnique, France

M. P. DesjarlaisSandia National Laboratories, New Mexico

Page 16: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.
Page 17: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

6: Nuclear activation

1 – Development of laser-plasma nuclear diagnostics

• choice of activation reactions with well-known cross sections;

• spectral, spatial and yield measurements of n, , ions;

• significant development work required for in-situ measurements in noisy plasma environment, using radiation hardened detectors;

2 – Innovative nuclear diagnostics

Examples may include:

• fusion reaction history measurements using gamma detectors (NIF) (D + T + 5He);

• charged particle detection to measure yield of neutronless reactions (e.g. D + 3He p (15 MeV) + 4He);

• Higher nuclear yields expected; observation of lower cross section and higher threshold energy reactions;

Page 18: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Effect of angle change with energy

Page 19: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Magnetic field generation during electron propagation is described by combining Ohm’s law with Faraday’s law:

fjE Ohm’s law

= resistivity

= fast electron current density

fj

Generates a magnetic field that pushes electrons towards regions of higher current density

Generates a magnetic field that pushes electrons towards regions of higher resistivity

ff jjB

EB

t

t

Robinson and Sherlock, Phys. Plasmas, 14, 083105 (2007)

Fast electrons

B field

Homogeneous plasma

laser

Resistive generation of toroidal B-field. B-field pinches the fast electron beam

Magnetic collimation

Page 20: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Results: Maximum proton energy

Ballistic transport and P. Mora PRL 2003 plasma expansion model.

sheatheppNppiBp netTkE /1~~,2/,)]1[ln(2 22

The scaling with target thickness is significantly different than expected from ballistic electron transport

Yuan et al., Vulcan TAP Fuchs et al., LULI (Nat. Phys. 2006)

Page 21: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Carroll et al, Phys. Rev. E 76, 065401 (2007)

Bea

m d

iver

gen

ce (

deg

rees

)

Proton energy (MeV)

Assume sheath profile

),()(),( max txHtFEtxE

0w

Ionizes hydrogen proton

Ion front profile

Sheath profile

Beam divergence

Good fit?

0w

NoYes

Measured divergence

0w

modify

Initial sheath diameter

Sheath expansion is modelled

Page 22: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

10um

Divergence

Source size

Model is benchmarked using grooved target results

Page 23: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Scaling of the collimation effect

Bell-Kingham theory: In the limit of substantial heating, collimation parameter:2

,2/15/2

sec5/22/1

511,10/3

511,5/15/25/25/3

23 )2(ln13.0 radpmffTW tRTTPZn

Page 24: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Electron temperature from LEDA simulations

Page 25: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

0 50 100 150 200 250

186

188

190

192

194

196

p / mec

log

(f 00(p

)) (

at o

bs.

ce

ll)

0 50 100 150 200 250

186

188

190

192

194

196

p / mec

log

(f 00(p

)) (

at o

bs.

ce

ll)

LEDAfit at 13MeVfit at 7MeVfit at 8MeV

Temperature variation

Black line is electron spectrum at rear surface of a 400 micron Al target

Red is fit using the input electron distribution and temperature (9.2 MeV)Same temperature!

Page 26: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Artificially increasing scattering:

Increase electron-ion scattering rate LogΛ = 2 → 10 → 100

Marginal effect on beam smoothness

Page 27: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Field duration variation

P Mora PRL 2003 plasma expansion model

0 500 1000 15000

10

20

30

40

50

60

Target thickness (um)

Ma

xim

um

pro

ton

en

erg

y (M

eV

)

p

2p

4p

Page 28: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

-600 -400 -200 0 200 400 6000

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5x 10

11

Position (um)

Ele

ctric

al f

ield

(V

/m)

E-field with space at peak field time

The temporal evolution is assumed to be a combination of Gaussian increase and exponential decrease.

This trend is supported by LEDA simulation, as well as the previous reports.

McKenna et al PRL 98, 145001 (2007)Kar et al PRL 100, 105004 (2008)

Electrical field transverse distribution is assumed to be parabolic function

Carroll et al PRE 76, 065401 (2007)Brambrink et al PRL 96, 154801 (2006)

),()(),( txHtFEtxE p

0)/exp(

0)2/exp()(

0

22

ttt

tttF

)(4/1),( 2 tpxtxH 2/)()( 2

0 vtwtp

-1 -0.5 0 0.5 1 1.5 2 2.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Page 29: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

-2 -1 0 1 2 30

200

400

600

800

1000

1200

1400

1600

Time (ps)S

heat

h fu

ll w

idth

(um

)

-800 -600 -400 -200 0 200 400 600 8000

1

2

3

4

5

6

7x 1011

Position (um)

She

ath

stre

ngth

(V

/m)

W0

Sheath size and source size with time

An example fit of beam divergenceExample sheath field profiles at different time

Page 30: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Transverse expansion velocity with time

From Patrizio Antici’s PhD thesis E Brambrink et al PRL 96, 154801 (2006)

Both suggest an exponential decrease of expansion velocity with time

Page 31: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Comparing simulation and experiment results

Simulation densities used in plasma expansion model

Page 32: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

Sheath size as a function of target thickness

Reduced growth in sheath size for thick targets

Lateral expansion of the fast electrons is limited

Self-induced fields become more important in thicker targets

Page 33: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

title

I = 5 x 1020 W/cm2

Lancaster et al., PRL 98, 125002 (2007) Green et al., PRL 100, 015003 (2008)

Target thicknesses ~100 µmDiagnostics:

•K emission•XUV emission•Shadowgraphy

Page 34: ICF-related research at Strathclyde Paul McKenna University of Strathclyde.

title

Fast electrondensity

Magnetic Fields