I i
Institute
off Shock
Sh k Physics:
Phy i
Initial
I i i l Experiments
E p i
A. Critchley, E. Price
A.
C
Critchley,
i hl E. Price
i
AWE Ald
AWE Aldermaston
de asto
Production of Large Scale Radiative Shock Waves
Production of Large Scale Radiative Shock Waves
Simon Bland, S.
Bland, S. V. Lebedev, G.
Lebedev, G. N. Hall, F.
Hall, F. A. Suzuki
Suzuki‐Vidal,
Vidal, A.
A. Harvey
Harvey‐Thompson,
Thompson, G. Swadling, A. G. Swadling, A. Marocchino, N. Niasse
Marocchino,
h
N. Niasse, J. Chittenden
, J. Chittenden
Imperial College London
Imperial College London
A Kinetic Drive for EOS and Hydrodynamics Experiments
A Kinetic Drive for EOS and Hydrodynamics Experiments
In an experimental arrangement used for astrophysics research,
research a thin metallic foil,
foil rather than discrete wires in stretched between a radial cathode and anode
Wire array z‐pinches
z pinches consist of cylindrical arrangements
of fine metallic wires,, that are imploded
p
byy fast risingg
mega ampere current pulses.
mega‐ampere
pulses
The high density (ni ~ 1022 cm‐3), high temperature (Ti
>500eV) plasmas created at stagnation of the array on
axis emit multi‐TW X‐rayy p
pulses that are used to drive
HEDP experiments,
experiments including ICF experiments.
experiments
Schematic
S
h
ti off wire
i
array z-pinch
ablation
1000s of tonnes/sec
0 25
0.25
P
Precursor
column
l
0
0
20
40
60
% of implosion time
100
Pre
esssurre (kba
ar)
By inclining the wires,
wires the
precursor is
i redirected
di t d outt off
the array into a plasma jet
Jet density
d
y varies as current2
exerting pressure of ~500kBar
500kBar
max over 100s
100 off ns
80
80
Plasma from
Pl
f
wires
20
350
400
450
500
Measure shock
breakout in multi
multithickness target
for EOS
Experimental images show formation of plasma jet and its dynamics en
en‐route
route to the target:
El t d
Electrode
16x18um W wires
Before the jjet has formed ablated
plasma from the array reaches the
f l The
foil.
h foil
f l is also
l p
preheated
h
d by
by
XUV emission.
emission
When the jjet reaches the foil it
interacts first with these plasmas
and multiple
p
bow shocks are
observed
XUV image @ 165ns
264ns after start of current on
215ns
195
195ns
2500
2500
500
The acceleration of the foil never approaches
th t expected
that
t d from
f
th jet
the
j t pushing
hi
on its
it
surface. Further at the time the jet arrives at
the foil,
foil the velocity profile suggests debris
flying
y g from its rear surface.
=> Initial
I iti l acceleration
l ti
f
from
ablated
bl t d plasma
l
before jet. Tip of the jet launches shock through
the foil,
foil producing spall
1000
500
0
100
200
287ns
300
Time (ns)
400
334ns
Estimated speed of foil
due to jjet
-1
1
Estimated
E
ti t d speed
d
without jet
1500
500
0
100
200
300
400
500
EExperiments
i
t pioneered
i
d att on the
th 20MA Z accelerator
l t att
Sandia National Laboratories have demonstrated the use
of magnetic pressure for ramp loading
Allows direct isentropic compression for EOS studies
b l
below
H
Hugoniot
i t to
t ~5MBar.
5MB Also
Al allow
ll
hi h velocity
high
l it flyer
fl
plate launching for shock EOS studies > 20MBar.
20MBar
ρv @ 230ns
S p e e d (m
m s -1 )
1500
1000
500
0
100
200
300
Time (ns)
( )
400
500
The
h pressure though
h
h is
i still
ill far
f lower
l
than simple calculations suggest
( 100kB ) 3D MHD simulations
(>100kBar).
i l ti
on
GORGON code show that the jet is very
narrow – pressure falls rapidly outside
of the jjet ((x100 if displaced
p
1mm))
Over nextt 12 months
O
th new experiments
i
t will
ill examine
i pressure profile
fil across jet
j t using
i line
li VISAR and
d multiple
lti l point
i t Het‐V,
H tV
redesign the experiment to improve repeatability and look at using just the ablated plasma as a kinetic drive
20
Z Ax
xis in mm
mm
No acceleration of the foil before
the
h jet
j arrives.
i
A l
Acceleration
i then
h ~
35x109 ms‐2 – 6x higher than
without
ith t the
th buffer.
b ff
This corresponds to ~ 14KBar
2000
Current Density @ 25ns
Current Density @ 36ns
Interferogram @320ns
Configuration for cylindrical
radiative
di ti shock
h k experiment
i
t
Interferogram @342ns
The MACH facility – a new generator for isentropic compression experiments
The MACH facility a new generator for isentropic compression experiments
A thin
thi plastic
l ti buffer
b ff foil
f il was placed
l d 2mm
2
b
beneath
th the
th Al target.
t
t The
Th foil
f il was designed
d i d to
t preventt the
th ablated
bl t d plasma
l
f
from
th array from
the
f
gathering
th i att the
th surface
f
off the
th Al foil,
f il and
d
also to prevent preheat from XUV radiation. Further when the jet reaches the foil it should act like a buffer mitigating the effects of the shock on the aluminium foil.
2
Ablated
plasma on
b ff ffoilil
buffer
D
Density
it @ 36
36ns
3mm polystyrene
p y y
sphere
1000
500
2500
D
Density
it @ 25
25ns
2mm stainless
steel sphere
p
Laser shadowgram @320ns
Time (ns)
Position of
Al target foil
Interferogram @335ns
2000
S ee
Sp
ed (m
ms )
S p e e d (m s -1 )
1500
Laser shado
shadowgram
gram @335ns
I t f
Interferogram
@ 263
263ns
The mechanism
Th
h i through
h
h which
hi h the
h shock
h k is
i launched
l
h d is
i still
ill unclear.
l
Experiments with small current pulses (to just melt the foil) demonstrate shock is not
caused byy release wave of the Al as it p
passes through
g p
phase transitions.
2D MHD simulations
i l ti
suggestt the
th argon immediately
i
di t l above
b
th foil
the
f il is
i ionised
i i d and
d a smallll
fraction of the current flows through this, forming a magnetic piston that snowploughs
up material in the radiative shock.
shock Later in time plasma that has ablated from the foil
reaches the shock front compressing
p
g the magnetic
g
field in the argon.
g
N
New
experiments
i
t will
ill probe
b the
th magnetic
ti field
fi ld through
th
h the
th shock
h k and
d the
th materials
t i l
upstream and downstream of it (optical spectrometry)
Whatever physical processes responsible,
responsible
the large
lar e scale shock wave
a e allows
allo s
extremely
well
diagnosed
shock
experiments to take place.
place
Now exploring experiments with shock
waves that
th t should
h ld interact
i t
t with
ith the
th
targets, and experiments in convergent
geometries
Comparison of acceleration of foil with calculation
2000
L
Laser
shadowgram
h d
@ 263
263ns
1cm
m
Het V velocity probe
Het-V
Jet
Bubble forms
inside shockwave
shock wave
Precursor
Drive modulated
target to drive
instabilities
Time (ns)
9um Al foil target
Cycle repeats
Filling the area above the foil with gas results in a radiative shock wave being launched from across the surface of the foil. This shock precedes the formation of the bubble above the
cathode With Ar gas at ~5mbar,
cathode.
~5mbar the radiative shock travels at ~60kms‐11
Backgro nd image
Background
0
300
Inductance
decreases
Inductance increases
Lbubble((t))
Magnetic
M
ti
probe
p
Could drive hydrodynamic
i t biliti
instabilities
(
(e.g.
R l i h
Rayleigh
Taylor) over long time scales
or apply ultra high pressures
to samples
p for EOS research
40
250
Current
C
reconnects
Surface of foil
60
200
2nd bubble
IInitial
iti l
current path
I iti l iinductance
Initial
d t
Lload
5.5cm diameter 6um Al foil, with
3 1mm cathode underneath
3.1mm
Side-on
Pinch
on axis
i (j
(jet)
t)
Collision of plasmas ablating
f
from
ffoilil leads
l d to
t precursor
column, mach stem on axis
100
Pressure predicted Pressure
predicted
from rocket
from rocket equation for 16‐
equation for 16
28mm W array on
28mm W array on MAGPIE
120
End-on
Collision of the of the coronal plasma
streams on the axis p
produces a
precursor plasma column.
column The
column
l
i inertially
is
i ti ll confined,
fi d remains
i
stable for ~100ns
100ns has temperatures
up to ~100eV and densities ~1019
ions
o s pe
per ccm‐3
0.75
05
0.5
Hohlraum
H
hl
for
f measuring
i
opacity of iron plasmas
1ccm
m
Long before implosion the wires evolve
into cold, dense cores that ablate into
warm low density coronal plasma.
warm,
plasma
C
Current
t remains
i concentrated
t t d close
l
t the
to
th
wire cores, accelerating this plasma
towards the axis of the array.
array
2
μ
I
dm
The rocket ablation model:
= o
dt 4π .rv
rv
Vacuum hohlraum
V
h hl
for
f inertial
i ti l
confinement fusion research
1
ra
adiu
us
240 x7.5um
75
W array
1st bubble
1st
st bubble
bubb e
15
10
5
5
10
15
20
25
30
35
0 m m a b o v e e le c tro d e
8 m m a b o v e e lle c ttro d e
1E10
P in pascals
p
1E9
1E8
1E7
-3
-2
-1
0
1
R a d iu s in m m
2
3
3.000E10
1.539E10
7.900E9
4.054E9
2 080E9
2.080E9
1 067E9
1.067E9
5.477E8
5.
77 8
2.811E8
1.442E8
7.401E7
3 798E7
3.798E7
1 949E7
1.949E7
1.000E7
Hugoniot – represents
passage of steady single
shock
h k wave
P
Pressure on target
g
material ~ B2
‘strip
strip line
line’ load configuration
used to apply magnetic
pressures to samples
from pulsed power I
generator
Diagnostics including
point VISAR
VISAR, Het-V
Het V, line
VISAR monitor motion
off ttargett material
t i l
I
B
Isentrope
V
For the ISP a new 2MA,
2MA 200ns rise time
pulsed
l d power facility
f ili is
i being
b i commissioned
i i
d
to drive strip line loads.
loads The generator is
b d on
based
LTD technology
t h l
with
ith 20
capacitor/switch units to allow precise
shaping of the current pulse and hence
magnetic
g
pressure .
p
Th LTD will
The
ill be
b compactt (<2.4m
( 2 4 diameter),
di
t )
and will not require insulating or SF6 –
minimising maintenance.
maintenance It will be easily
stackable to increase voltage
g to drive higher
g
inductance imploding plasma loads.
inductance,
loads
Multiple diagnostics are also being
d l
developed
d including:
i l di
• Fibre based point Het‐V
Fibre based point Het V
• Point VISAR
Point VISAR
• Line VISAR
• Fibre based quadrature Fib b d
d t
interferometer
0.02
S nal ((AU)
Sign
Bθ
The foil
Th
f il melts
l and
d appears to move 0D like
lik
Gap opens up near cathode and plasma
bubble accelerated,, whilst p
plasma column
stagnates on axis
Reconnection at the cathode leads to
further bubbles
Previous
P
i
current path
h
1st bubble
1cm
m
j xB
jz
MACHs little sister,
sister the 1MA MAIZE generator at
University of Michigan (picture thanks to R.Gilgenbach)
R Gilgenbach)
0.00
-0.02
-0.04
100
150
200
250
300
Time (ns)
350
400
450
500