1

A New Twist to IFE- Impact Ignition -

Contents of talk・What is Impact Ignition!?・ Gain model・ Design window・ 2D hydrodynamic simulation・ Cone shell experiments

In collaboration with H. Nagatomo,1 K. Nishihara,1 H. Shiraga,1 H. Azechi,1 Y. Izawa,1 F. Ogando,2 P. Velarde,2 M. Perlado,2 and S. Eliezer3

M. Murakami　　　 Institute of Laser Engineering, Osaka University

2

New Scheme: Impact Ignition - Target Structure and Flow Diagram -

Time

Radius

Main DT fuel

Fast implosion for fast ignition

Shock

Laser

Laser orX-ray radiation

Compressedmain DT fuel

Impact-produced igniter Impact collision

to form a hot spot

Cone guide

vimp≈108 cm

sec

τL ≈O(n )sec

Ablator

DT layer

3

Advantages of Impact Ignition

(1)Simple Physics

(2) High Efficiency

(3) High Robustness

(4) High Gain

(5) Low Cost

Laser

Laser orX-ray radiation

Compressedmain DT fuel

Impact-produced igniter

Cone guide

τL ≈O(n )sec

Ablator DT layer

(6) No need for PW Laser

4

Gain Model

2 Rs

2 Rc

Impact-produced DT igniter

Compressed main DT fuel

ρs

ρc

vimp =(12Ts /5mp)1/2 =1.1×108(cm/sec)

ELs =8πHs

3Ts

5mpηsρs2 =15kJ ⋅ηs

−1 ρs

100g/cm3

⎛

⎝ ⎜

⎞

⎠ ⎟

−2

ELc =3.3×1012αcρc2/3M c /ηc

Ed =ELc +ELs

Φ =Hc /(Hc +H0)

G =ΦM cε0 /Ed

Implosion velocity

Laser energy for igniter

Laser energy for compression

Total driver energy

Burn fraction

Energy gain

5

Gain curves for Impact Ignition Targets

10

100

1000

10 100 1000

Total Driver Energy (kJ)

αc = 3, ηc = 0.1, η i = 0.1

200

ρc (g / cm3 ) = 100

300

ρi (g / cm 3) = 100

200

300

6

Impact Ignition can be designed in other illumination schemes

Laser DirectLaser Indirect

HIB Indirect

Laser

HIB

Laser

HIB Indirect

7

Non-uniform implosion can achieve higher ρR values.

Uniform implosion

Non-uniform implosion

8

Cone shell target

X-ray image of the compressed fuel plasma

Efficiently compressed core can be generated even by nonuniform implosion

Those experimental results have been published in Nature (2001 & 2003).

9

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(a)(b)200 μm190 μm Time integratedFig. 7

10

Implosion experiment of cone-shell target at LLE OMEGA laser

CH shell:1000 μm μmt, D2 5 atm

Laser: 35 beams 15 kJ/1 ns SQ (8x1014W/cm2 )

X-ray emission from core and cone tip Ultrafast x-ray image (t=10 ps) obtained with MIXS: Multi-Imaging X-ray Streak Camera with PJX at LLE

70deg Au cone

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200 μm x 200 μm

core cone

by H. Shiraga, S. Fujioka, P. Jaanimagi, C. Stoeckl, et al.

11

Different irradiation schemes for indirectly driven HIF- History of designs to kill low mode asymmetries -

But those are for spherical fuel pellets!!

12

Impact Ignition may allow us different beam options beyond standard parameters.

I will talk a bit more details on this topic in US-Japan Workshop after this symposium.

13

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14

2D Hydrodynamic Simulation

Isocontour map at a time shortly before the impact

Isocontour map at peak comp-ression shortly after the impact

15

DYNAMICS OF A SPHERICAL ROCKET

Equation of motion

Assuming quasi-stationary Chapman-Jouguet deflagration,

Implosion velocity and Radius arethen given by the temporal mass

MdV

dt=−4πRPa

dMdt

=−4πRm

⎧

⎨⎪

⎩⎪

Pa :ablationpressure

m:massablationrate

mu≈ρCJcCJ ≈PCJ =Pa / χ (χ =const≈1.)

M(1−lnM) =1−α(1−R3) /3

V /u=χ lnM

(M ≡M(t) /M0 , R ≡R(t) /R0 )

Thus the shell implosion is described by a dimensionless parameter

α =mR0

ρ0χuR0=

PCJ

Pa

ρCJ

ρ0

R0

R0

R0 / R0 : initialshellaspectratio

ρ0 : initialmassdensityβ

β

β

16

Hydrodynamic Efficiency

.

0

5

10

15

0 0.2 0.4 0.6 0.8 1

Μ/Μ0

0.6 < Μ/Μ0< 0.8

f(M) =9914

M ln M(1−M) +M lnM

ηh =ηhmaxf(M)

17

Scaling laws for laser-driven ablation

Mass density at the sonic point:

Energy balance:

ρC−J ≈ρcrt

ηaI L ≈4ρC−J uC−J3

Åú

Åú

ρCJ (g/cm3) =3.7×10−3λL−2

cCJ (cm/sec)=8.8×107(Ia15λ2)1/3

m(g/cm2 ⋅sec)=3.3×105 (Ia15λL−4)1/3

Pa(Mbar)=43(Ia15λL−1)2/3

⇓

18

Design Window for Laser and Target Parameters

0.95≤ηh /ηhmax≤10.15≤ ˜ M ≤0.35

0.085≤Ia15λL2 ≤0.50

λL =0.35μm 0.69≤Ia15≤4.1

68≤Pa(Mbar)≤220

3.0≤ρa(g/cm3) ≤6.0 (αs =5)

0.97≤β≤1.9⇒

⇒

19

High isentrope suppresses Rayleigh-Taylor Instability

γRT = kg/(1+kL) −3kva

R0 ≥R ≥R0 /2

Γ ≡ γRT∫ dt= l /(1+δlΔR/ R) −3l(R /ΔR)(1− ˜ M )

Γ =ln103

l =2πR /ΔRR / ΔR ≤95

171αs−3/5 ≤R/ ΔR ≤387αs

−3/5 3≤αs ≤6

Under constant acceleration for

⇒

⇒

20

Summary

• A totally new ignition scheme, Impact Ignition, has been proposed.

• Impact Ignition has very attractive features.

• Major breakthrouh expected in future experiments is to demonstrate high implosion velocities at low isentropes.

21

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22

Direct drive for the igniter shell has much higher potential to achieve Impact Ignition than indirect drive

Advantages:

(1) Laser pulse shape and irradiation timing can be rather freely designed.

(2) With high specific deposition power, the exhaust velocity and thus the implosion velocity is quite controllable.

(3) Experiment can be conducted under orthodox laser systems (Gekko XII) with no special know-how for the target fabrication and optical design and operation.

23

In indirect scheme, it is hard to achieve high implosion velocities for the ignitor shell

Implosion velocity: vimp =χcC−J ln(M0 /M)

:Sound speed cC−J =(Z+1)kBT

Amp

T =300eV, χ ≈1., (Z+1) / A ≈1/ If we assume

:Remaining mass

vimp=3×107cm/ s ⇒ M / M0 =19.0%

vimp=6×107cm/ s ⇒ M / M0 =3.%

Feasible

Very hard!