COMPRESSION OF FIELD REVERSED CONFIGURATIONS FOR MAGNETIZED TARGET FUSION

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COMPRESSION OF FIELD REVERSED CONFIGURATIONS FOR
MAGNETIZED TARGET FUSION
Presented at Symposium on Current Trends in
International Fusion Research 7-11 March 2005
presented by Dr J. H. Degnan Air Force Research
Laboratory Directed Energy Directorate
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COMPRESSION OF FIELD REVERSED CONFIGURATIONS FOR
MAGNETIZED TARGET FUSION
J.H.Degnan, A. Brown (2), T.Cavazos (1),
S.K.Coffey (2), M.Frese (2), S. Frese (2), D.Gale
(1), C.Gilman (1), C. Grabowski (1), B. Guffey
(2), T.P.Intrator (3), R.Kirkpatrick (3),
G.F.Kiuttu, F.M.Lehr, R.E.Peterkin, Jr (1),
N.F.Roderick (4), E.L.Ruden, R.E.Siemon (5),
W.Sommars (1), Y F. Thio (6), P.J.Turchi (3),
G.AWurden (3), S. Zhang (3) Directed Energy
Directorate, Air Force Research Laboratory,
Kirtland AFB, NM, USA (1) SAIC, Albuquerque, NM,
USA (2) NumerEx, Albuquerque, NM, USA (3) Los
Alamos National Laboratory, Los Alamos, NM,
USA (4) Permanent address Department of Chemical
and Nuclear Engineering, University of New
Mexico, Albuquerque, NM, USA (5) University of
Nevada Reno, Reno, NV, USA (6) DOE-OFES This
research was sponsored by DOE-OFES
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Elements Of Magnetized Plasma Compression, aka
Magnetized Target Fusion (MTF)
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MTF Is A Hybrid Of ICF And MFE

• ICF relies on rapid imploding boundary to achieve
  adiabatic compression of fuel- requires driver
  to deliver megajoules in nanoseconds- requires
  several 10s cm/microsecond implosion velocity-
  validated by underground tests
• MFE relies on magnetic field to confine modest
  density, high temperature plasma for seconds or
  longer- problems are instabilities and
  impurities- has achieved gain 0.5 (gain
  energy out/energy in)
• MTF uses magnetic field to suppress thermal
  conduction , imploding boundary to compress
  plasma- requires 10s of megajoules in 1 to 10
  microseconds- requires 1 cm/microsecond
  implosion velocity- greatly reduced driver power
  (x100 to 1000) relative to ICF

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Magnetized Target Fusion
LANL

• Magnetized target fusion (MTF) identified in US
  and Russia as an alternate approach intermediate
  between MFE and ICF parameter regimes
• Closed magnetic field configurations reduce
  electron thermal conduction losses
• Enables (slower) adiabatic compression with
  modest driver requirements
• 10X radial compression required
• Typical precompression plasma parameters 100 eV,
  1017 cm-3, 5 T

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Field Reversed Configuration Self Organized
Magnetic Equilibrium
LANL

• Closed magnetic field lines
• Magnetic field line tension squeezes axially when
  radially compressed
• Particles that drift across flux surfaces are
  lost to open field lines beyond separatrix
• Equilibrium lifetime is anomalously long (many
  Alfven times), but not theoretically understood

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Diagnostics
LANL

• Initial diagnostics for FRC formation
• Diamagnetic field exclusion magnetic probe array
• Radial view laser interferometry
• Axial view fast photography
• Current and voltage probes on all discharges
• Later additional FRC formation diagnostics
• Vacuum ultraviolet (VUV) probe arrays for purity
  monitoring and temperature, density information

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AFRL eight chord laser interferometer installed
on FRC formation system at LANL
 
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Density vs. time at various radii via Abel
Inversion.
The radii chosen correspond to the closest
approach of each laser chord to the FRC axis
(impact parameters). Shot 1973
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Density vs. radius at various times for FRC
inferred from Abel Inversion algorithm.
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FRC status as of mid 2003 achieved parameters
are approaching pre-compression goals
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FRC Compatible Imploding Liner Hardware Design
- The 30 cm long liner implosion experiments
extend our experience to longer liners - The
diagnostics on these initial shots include flash
radiography, interior magnetic field
compression, discharge current and voltage, and
an interior instrumented impact package
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Shiva Star Facility at AFRL

• 82 kV, 1300 uF, 44 nHfor first Z-pinch driven
  long liner experiments
• 12 Megamp, 10 ?sec risetime discharge implodes
  30 cm long, 10 cm diameter, 1.1 mm thick Al liner
  in 24 ?sec
• 4.4 MJ energy storage gives 1.5 MJ in liner KE

Shiva Star Capacitor Bank (up to 9 Megajoules, 3
?sec) available now for implosion - compression
experiments
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Radiographs from FRC compatible Liner Implosion
on Shiva Star
t 0.0 ?sec, diam 10 cm
Achieved velocity, radial convergence, symmetry,
stability needed for compression of FRCs to MPC
conditions
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Avoiding Sliding Liner-electrode Contact

• Avoiding the sliding liner-electrode contact is
  desirable in order to
• - Avoid impeding FRC injection into interior of
  liner - Improve purity of injected FRC
• Improve axial diagnostic accessTwo approaches
  to achieving this are
• Using deformable liner-electrode contact for
  Z-pinch driven liner
• Using a theta-pinch driven liner

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Connecting current to the liner
Uniform-thickness liner
Variable-thickness or shaped liner
Liner
Glide-plane electrodesused in 1999 Shiva-Star
experimentswould interfere with FRC injection
Shaped liner recently tested
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2D-MHD simulations indicate feasibilty of
deformable liner-electrode concept
Double frustrum profiled liner density contours
at 1 ?s before peak compression
Double frustrum and smooth liner initial
thickness profiles
Smooth profiled liner density contours at 1 ?s
before peak compression
Deformable Liner-Electrode Contacts Offer
Advantages in Purity of the Compressed Plasma and
Diagnostics Access for Z-pinch Driven Liner
these examples are for 8 cm diameter electrode
apertures
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Deformable contact liner implosion performed with
8 cm diameter electrode apertures results
indicate that Z-pinch imploded liner approach is
feasible
Static radiograph of portion of liner adjacent to
electrode, prior to experiment. Inner diameter
9.78 cm.
2D-MHD simulated density contours for similar
parameter liner implosion, at 0.5 ?s before
stagnation.
Experimental radiograph for portion of liner
adjacent to electrode, at 22 ?s after start of
current, approximately 0.5 ?s prior to peak
compression. Bottom of liner to top of field of
view is approximately 4.5 cm.
Overlay of 2D-MHD simulation density contours and
radiographs at approximately same size scales.
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Mid-gap radiograph indicates 17 x radial
compression of inner surface
Top radiograph of liner at t0, near mid-gap, ID
9.78 cm, OD 10.0 cm. Bottom radiograph of
liner at t 22 ?sec, near mid-gap. ID of non-m0
portion ? 0.58 cm, corresponding to radial
compression of inner surface 17. We believe
that the m0 portion is right at mid-gap. If
there had been an FRC inside, it would be
compressed gt 10x radially prior to significant
growth of this instability.
We suspect this late m 0 feature is due to
release of initial axial compression, combined
with thickness derivative discontinuity (from
double frustrum thickness profile) at 9 cm from
mid-gap. Both the initial axial compression and
the thickness derivative can be removed by design
change.
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Axial view fast optical photos indicate symmetric
implosion of inner surface of liner with inner
diameter consistent with simulation
Left 200 nanosec optical framing photo, axial
view, of load. Inner diameter of opening is 8.0
cm. Photo used Xenon flash backlighting. Right
200 nanosec optical framing photo, axial view, of
load at 21?sec into implosion discharge. Inner
diameter of smallest part of liner (most imploded
part) is 1.5 cm.
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An 1 mil (.025 mm) thinning of liner over
central cm near mid-gap would explain late m 0
feature
t 21 ?s
t 22 ?s
Z 15 cm mid-gap
Z 0 cm
R 4.0 cm
R 0 cm
Mach2 2D-MHD simulation density contours for half
height of liner at t 21 ?s and 22 ?s for double
frustrum liner thickness profile from z 0 to 6
cm, uniform thickness 1.1 mm from z 6 to z
14.5 cm, thickness tapers from 1.10 to 1.075 mm
from z 14.5 cm to mid-gap. Electrode aperture
radius is 4 cm.  
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Alternative liner thickness vs profiles are being
examined via Mach2 simulations
A family of such simulations uses an analytic
profile which includes Gaussian thinning region a
few cm from electrodes
Z0 distance from liner midplane. Zo 11.5
corresponds to 3.5 cm up from electrode. Z00
3.5 ? is the half width at half max and ? is a
measure of the amplitude. Other parameters are
defined in following table (next slide)
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Deformable liner thickness profile parameters
R0 R1 z1 z0
? ?
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2D-MHD simulations indicate that use of Gaussian
thinning regions a few cm from electrodes
controls divergence of liner ends variants of
this are being investigated computationally
mid-gap
15 cm
4 cm electrode inner radius
Baseline 01
03 05 06
07
07-1 07-2
08 08-1
09 09-1
Contour plots show half (15 cm) of 30 cm tall,
5 cm initial outer radius, Al liner position and
shape at 21 microseconds after start of 1300
microfarad, 80 KV, 44 nanoHenry initial
inductance Shiva Star discharge, with standard
safety fuse. Initial liner thickness is 1.1 mm at
mid-gap (15 cm above lower electrode).
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Normal current delivery to liner and symmetry
were obtained for experimental Bi-frustrum
profile)case
Current peaked at 12 megamps, at 10 ?s after
start of current rise. Insulator crowbar occurred
at 17 ?s, as expected.
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Simulation Details FRC Formation and Translation

• The FRC formation uses a flux-based resistive
  diffusion model.
• The simulation includes
• Thermal diffusion
• Radiative emission
• After about 2 ms, the forming FRC translates
  itself down the formation region into the liner
  implosion region.
• We generally use an FRC from 4 ms into the
  formation simulation to insert (interpolate) into
  the imploding liner simulation.

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FRC Formation and Injection Setup
Schematic (not to scale)
Formation And Translation Region
Implosion Region
Liner (not in formation/translation phase)
m
axis
axis
t

0
.
0
0
0
0
0
E

0
0
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FRC Formation and Translation Te Flux
Liner Implosion Region
t 0 ms
t 1 ms
t 2 ms
t 3 ms
t 4 ms
t 5 ms
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Integration of the Two Simulations

• Around 13 to 14 ms, we interpolate the FRC
  simulation data into the liner implosion
  simulation and continue the implosion.
• We can vary the time of the insertion (relative
  to the liner implosion) and the age of the FRC.
• The following series of figures shows the liner
  (in white), the temperature, and the flux lines
  as the liner implodes.
• In this particular simulation, an FRC 4.2 ms old
  is inserted into the liner at 13 ms as shown at
  right.

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Early Liner Evolution with Injected FRC

• The downward momentum of the FRC tries to force
  it out the bottom of the liner.
• The mirror field trapped in the imploding liner
  captures it, but some mass escapes.

t 13 ms
t 13.5 ms
t 14 ms
t 14.5 ms
The white line is the liner.
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Liner Evolution with Injected FRC
t 15 ms
t 16 ms
t 17 ms
t 18 ms
t 19 ms

• This combination of timings seems to capture and
  re-center the FRC.
• The grid motion is stopped at 17.4 ms
• The lower portion of the grid is shown in the
  inset

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Late Liner Evolution with Injected FRC

• By 20 ms, the liner has com-pressed to an inner
  radius of 0.5 cm.
• The temperature in the center of the FRC is over
  8 keV.
• There are temperatures as high as 13 keV within
  the FRC, near the axis.

t 19.5 ms
t 20 ms
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Design concept for integrated FRC formation
hardware with imploding liner compression
hardware is evolving - adequate space for
existing FRC formation load hardware design in
vertical orientation under Shiva Star center
section with implosion load hardware - even more
space available with re-positioning of FRC vacuum
pump
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Presently planned layout of FRC Formation
Hardware Under and Around Shiva Star

• Main single re-configured Shiva Star module
• PI pre-ionization bank
• Bias, guide, and cusp banks in NE sextant of
  floor space
• rail mounted FRC formation train is under
  Shiva Star B transmission line when mated to
  implosion chamber
• rail mounted FRC formation train is withdrawn
  to NE corner of workspace for FRC formation
  experiments with greater formation diagnostics
  complement, allowing other uses of Shiva Star

FRC formation load in axial orientation
Re-configured Shiva Star module
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Can Imploding Liner Magnetized Plasma Compression
Be Made Repetitive?

• Implosion-compression of several-cm-radius shells
  on the 1 to 10 microsecond time scale can be used
  for magnetized target fusion (MTF)
• This can be done in a manner with standoff of the
  driver, e.g., using arrays of laser or particle
  beams, which enables repetitive operation (for
  power plants or propulsion)
• Similar to inertial confinement fusion (ICF)
  drivers, but with 103 to 104 times slower pulses,
  hence easier
• There are also schemes for repetitive operation
  of magnetic pressure driven liner implosions
  (R.W. Moses et al, LA-7683-MS, 1979), and for
  pneumatic pressure driven implosions of
  rotationally stabilized, re-usable liquid Li
  liners (P.J. Turchi et al, Phys. Rev. Lett. 36,
  1613 (1976))
• A plasma jet spherical array compression scheme
  has also been proposed (Y.C.F.Thio et al,
  Proceedings of Second Symposium of Current Trends
  in International Fusion Research, 1999)
• Single shot versions of such implosion-compression
  can be done now via magnetic pressure
  implosions, using our existing large capacitor
  bank
• Such single shot implosion-compression
  experiments can be used to investigate critical
  technical issues before developing and building
  more expensive, repetitive drivers