Diapositiva 1

1
Jets on a Stick
D. Martinez , L. Waxner R. Presura
Conical Wire Arrays
Why We Care

• Stabilization of current carrying plasma
• To support theoretical work on sheared flow
• To better understand the formation of stars

Conical wire arrays allow us to look at the start
of a plasma jet.
Current is split depending on the size of the
inner wire
Ablated plasma flows perpendicular to the wires
causing the outer plasma to have a axial and
radial component.
As seen in these images, Astrophysical jet remain
collimated over distances much larger than there
radii. Current theories suggest that these jet
are self collimated by magnetic fields 1,2,3
which as we know from Z-pinch experiments is
normally unstable.
The Plasma from the center wire stagnates and
interacts with the outer wire plasma causing a
sheared flow with a no slip boundary condition
A conical shock is formed from the incoming
plasma. Once plasma passes this boundary the
velocity profile becomes axial dominated4.
Experiment Setup
Zebra
Short Pulse 1MA Peak, 90ns Rise Time Long
Pulse 0.6MA Peak, 200ns Rise Time
Wire Array Configurations Used
Shot Array Type CW diam. CW Mat OW diam OW mat Inner diam. Outer diam.
1083 Conical N/A N/A 15 µm Al 5056 6.2 mm 19 mm
1084 Conical N/A N/A 15 µm Al 5056 6.2 mm 19 mm
1088 Conical 50 µm Cu 15 µm Al 5056 6.2 mm 19 mm
1089 Conical 10 µm Al 5056 15 µm Al 5056 6.2 mm 19 mm
1092 Conical 50 µm Al 5056 15 µm Al 5056 6.2 mm 19 mm
1095 Cylindrical N/A N/A 15 µm Al 5056 12.5 mm 12.5 mm
1097 Cylindrical 50 µm Al 5056 15 µm Al 5056 12.5 mm 12.5 mm
1100 Cylindrical 10 µm Al 5056 15 µm Al 5056 12.5 mm 12.5 mm
In this set of experiments we chose our arrays to
investigate the various parameters that might
play a role in the sheared flow of plasma. In
this poster we are focusing on the difference
from a conical wire array with a central wire and
without. We also looked at the effects from a
center wire made of different materials.
Marx Charged to 85 kV 100
kV Stored Energy 150 kJ
200 kJ
discussed in detail in the results section
Diagnostics
Laser diagnostics
X-ray diagnostics
The laser diagnostics include Faraday, Shadow and
Interferometry. We use these diagnostics to
observe the collimation of the plasma at
different points in time.
Ch 2
PCD Looking at the x-ray emission from the wire
arrays. In these shots we observed spikes in the
x-ray emission corresponding to the a localized
pinch or the explosion of the center wire.
Frame 1 0ns Frame 2 6.2ns Frame 3 12.4ns Frame
4 18.8ns Frame 5 25.0ns Frame 6 30.8ns
Ch 1
Schlieren
Pinhole images We used a time gated pinhole
camera in addition a time integrated pinhole
camera to observe the hotspots in the plasma.
Ch 3
Image type Ch1 Ch2 Ch3 Ch1 delay Ch2 delay
Delay from first frame 0ns 2.19ns 3.88ns 6.63ns 8.82ns
Results
Without a center wire
Shot 1084
Shot 1083
2s 1084
2d 1084
We can see instablites
Small kinking structure is forming in the plasma
jet
Copper center wire
Al 5056 Center wire
We see a bright center surrounded by a plasma
shell which we think is the center wire exploding
and the wire array imploding
This instability that has formed on the inside of
the conical shock looks like Kevin Helmholtz
instability. In only 7ns we can see that the
instability has grown at an alarming rate.
The conical shock is easily seen from the shadow
images
Again we see the center wire exploding
References
Conclusions
Future work
Currently we are working on futher anylizing the
data obtained form this series of shots by
looking at the plasma temperature for ratios in
the spectra lines. In future experiemnts we plane
to use a high resolution spectrometer to observe
the doppler shift in the jet to help detriment
the outside shear flow.
In the current state of research we can see that
shear flow does help stabilize the plasma. The
center wire plays an important role of the
formation of the precursor plasma but does not
contribute to the stabilization of the plasma due
to its early explosion. The use of Aluminum wires
has shown some unusual results that needs to be
further investigated. As for temperature of the
plasma we do find that the conical wire arrays
with a center wire do produce more energy than
ones without.