Laser-Produced High-Energy-Density Plasmas

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16 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Imploding

cone
-
in
-
shell
capsule

2.7

mm

15
-
MeV proton

backlighter

Imaging detector

Protons per unit area on detector

protons

Proton Radiography of Electromagnetic Fields in

Laser
-
Produced High
-
Energy
-
Density Plasmas

HEDLP Workshop
Washington DC August 08

C. K. Li MIT

MIT

Summary

Time
-
gated, monoenergetic proton radiography
provides unique measurements of E+B fields in
laser
-
produced HED plasmas



Radiography of laser
-
foil interactions:



Observation generations of ~10
6

gauss
B

field and 10
9

V/m
E

field


Observation of decay dynamics and instabilities of MG
B

field


Observation of field topology change due to magnetic reconnection



Radiography of direct
-
drive cone
-
in
-
shell/spherical implosions:



Observation of radial, filamentary structures with complex striations and
bifurcations, of
B

field magnitude 0.6
×
10
6

gauss


Observation of radial
E

field of order 10
9

V/m and its direction reversal




Radiography of laser
-
irradiated gold hohlraums:



Observation of ~10
6

gauss
B

field and its evolution


Observation of ~10
9

V/m
E

field and its evolution






LLE
-
UR


R. Betti

J. Delettrez

V. Goncharov

J. Knauer

F. Marshall

D. Meyerhofer

V. Smalyuk




Collaborators

MIT


F. Séguin

J. Frenje

R. Petrasso

M. Manuel (G)

D. Casey (G)

N. Sinenian (G)



LLNL


P. Amendt

O. Landen

J. Rygg

R. Town





GA


C. Back

J. Kilkenny

A. Nikroo




The proton source is a laser
-
driven glass capsule

filled with D
2

and
3
He gas

0

10


20

6
×
10
8












0

(MeV)

protons

MeV

source spectrum

3% FWHM

3
×
10
18












0

(ns)

protons

s

0

0.5


1

source emission

130 ps

FWHM

14.7 MeV protons

D +
3
He

4
He +
p (14.7 MeV)

Heating of the gas during implosion

leads to nuclear fusion production:

Source

Emission of 14.7 MeV D
3
He protons is pulsed, monoenergetic, and isotropic

PRL 2006

Radiographs of laser
-
generated plasma bubbles on opposite
sides of a foil prove that deflecting fields are
B

rather than
E


OMEGA shot 46535






d
B
ξ

p
v
p
m

A
a)
-
qa(A
a

A

Petrasso et al APS 2007

Data and LASNEX simulations are similar with
the laser on, but diverge afterwards

Interaction laser

on for 1 ns


5mm

Outer bubble

Burn
-
through hole

0.3 ns 0.6
0.9
1.2 1.5 1.8 2.3 3.0 ns


0
500
0
1
2
3
Time (ns)
0
0.6
Laser power (TW)
0
2000
0
0.6
Laser power (TW)
Mean

bubble

radius

(µm)

(a)

(b)

RMS
bubble

asymmetry

(µm)

0
250
0
1
2
3
Time (ns)
0
0.6
Laser power (TW)
(c)




B

d



(MG
-
µm)

2D code LASNEX produces credible simulations of the hydrodynamics and field
growth as long as the laser was on, failing only when 3D instabilities appeared.

LASNEX+LSP by R. Town

PRL 2007a

0
200
0
1
2
3
4
5
Position along lineout (mm)
Magnetic
reconnection

has been observed and quantified

5 mm




B

d



(MG
-
µm)

0.31 ns 0.51 ns 0 .69 ns 0.97 ns 1.24 ns 1.72 ns 2.3
5 n
s



5mm

0.04 ns 0.67 ns 1.42 ns





B

d



(MG
-
µm)


0
200
0
1
2
3
4
5
Position along lineout (mm)
> 95% field strength was
reduced in the region
where bubbles overlap

PRL 2007b

Face
-
on 15
-
MeV radiographs show the evolution

from “corrugated” to cellular structures





0
1
2
3
Time (ns)
Drive laser


~0.6 MG fields in these
cellular structures with
cell size ~ 120
μ
m

Position (
µ
m)


P
-
P amp. ~ 18%


Position (
µ
m)


P
-
P amp. ~ 5%



Diameter = 2.5 mm

Thickness = 20
±
1
m
m

Modulation

~ 120
m
m

P
-
V modulation ~ 0.5

m
m

“ linear” (2D)

Petrasso et al APS 2007

0
100
200
300
400
500
0
0.5
1
1.5
2
2.5
r
(
m
m)
t (ns)
envelope of high shell density
proton arrival (a.u.)
drive pulse
Radiography of a cone
-
in
-
shell capsule implosion reveals
field topology and capsule compression

Fluence

Energy

14 kJ laser drive

filamentary field structures

radial focusing E
-
field

capsule compressed

by a factor of two

cone shadow


Rygg et al Science 2008

Time
-
gated proton radiography of direct
-
drive ICF
spherical implosions provides the spatial structure and
time evolution of E+B fields

0
0.5
1
1.5
2
Time (ns)
Drive laser

3

mm

Fluence

Seguin et al APS 2007

The reversal of proton fluence focusing indicates
the
direction change of

a self
-
generated radial
E

field

0.8 ns 1.2 ns 1.4 ns

1.6 ns 1.9 ns 2.1ns

10
1
5


10
10

10
5


0


-
10
5


-
10
10


-
10
1
5


0
1
2
3
Time (ns)
E

(V/m)

Data


Simulation

PRL 2008

2mm

7mm

Radiograph E+B fields generated inside Au hohlraums
with protons (DD and D
3
He) and with alphas (D
3
He)

B

B

before reconnection

after reconnection

OMEGA
-
Scale 1.5

10 beams (1ns
-
square,SG4+SSD)
from Cone 3 drive the hohlraum

21 beams drive
the backlighter

Fields

are

very

important

for

:


understanding

ignition

experiments

at

the

National

Ignition

Facility
.



laboratory

astrophysics

of

plasmas

with

lower

β

(~
1
)

0
0.4
0.8
0.0
0.5
1.0
1.5
2.0
2.5
Distance (mm)
Protons
μ
m
-
2

2.6 mm

t = 0.52 ns

Observation of ~10
6

gauss
B

field and ~10
9

V/m
E

field
and their temporal evolution have been made

LASNEX+LSP simulation
by R. Town

MIT

Summary

Time
-
gated, monoenergetic proton radiography
provides unique measurements of E+B fields in
laser
-
produced HED plasmas



Radiography of laser
-
foil interactions:



Observation generations of ~10
6

gauss
B

field and 10
9

V/m
E

field


Observation of decay dynamics and instabilities of MG
B

field


Observation of field topology change due to magnetic reconnection



Radiography of direct
-
drive cone
-
in
-
shell/spherical implosions:



Observation of radial, filamentary structures with complex striations and
bifurcations, of
B

field magnitude 0.6
×
10
6

gauss


Observation of radial
E

field of order 10
9

V/m and its direction reversal




Radiography of laser
-
irradiated gold hohlraums:



Observation of ~10
6

gauss
B

field and its evolution


Observation of ~10
9

V/m
E

field and its evolution