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Target threat spectra
Gregory Moses and John SantariusFusion Technology Institute
University of Wisconsin-Madison
HAPL Review MeetingMarch 3-4, 2005
Naval Research LabWashington DC
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Outline
• Target debris transport to wall modeling– Monte Carlo “splitting” algorithm implemented
• Bounding threat spectra calculations– NRL meeting on December 9, 2004– Pure hydro calculation– Long mean free path calculation
• BUCKY explosion simulations
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“Conventional” target chamber simulation
Time of flight spreading asions reach wall leads to coarsefinite particle approximation
E
N
Ion energy distribution sampled at discrete energies Ei
Target explosion
Split particles at R* to giveresolution as they impingeon first wall
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Target debris transport to wall: wall surface temperature for different splitting parameters
0 0.5 1 1.5 2 2.5
x 10-6
0.1
0.15
0.2
0.25
Time (s)
Tem
pera
tue
(eV
)
Wall Surface Temperature vs Time
No splitting10:1 splitting100:1 splitting
160 MJ NRL target50 mTorr Xe gas6.5 m radius
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Bounding threat spectra calculations
• Meeting at NRL on Dec 9, 2004– Post-burn exploding target has ion mean free
path “issues” that potentially reduce the shock acceleration of the plasma debris.
– HANE experiments and theory are relevant to these issues. Instabilities could produce effective collisionality that “re-validates” hydrodynamics model. (Ref: R. Clark, et. al.)
– First step: bounding calculations with models currently in BUCKY.
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Bounding threat spectra calculations High collisionality – pure hydrodynamic
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Bounding threat spectra calculations High collisionality – pure hydrodynamic
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Bounding threat spectra calculations High collisionality – pure hydrodynamic
4x108 cm/s
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Wave-Particle Interactions May Cause theHydrodynamic Approximation to Remain Valid
• This mechanism was pointed out by NRL during the NRL/UW physics meeting on Dec. 9.
• Instabilities and wave-particle interactions caused hydrodynamics to be a good approximation for the HANE experiments.
• Bob Clark’s poster at this meeting, based on HANE program research during the 1970’s, very nicely summarizes the potential instabilities and coupling mechanisms.
• Work has begun on this mechanism for HAPL.– Caveat: Devil is in the details, and the problem is very difficult.
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• Each point represents a Lagrangian zone of constant mass.
Shock Parameters at 34.586 ns (Ignition Plus ~20 ps)Show That the Shock Has Reached r = 0.02-0.03 cm
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Ener
gy (k
eV)
Bounding threat spectra calculations Low collisionality – kinetic fast ions
Hydrodynamic calculation of ion
energy in shock frame
Kinetic calculation of energy gained by ion
• At ~34.586 ns, hydrodynamic and kinetic energy deposition calculations begin to diverge.
• A separate BUCKY calculation will stream the shock ions through the ambient plasma.
DT-CH shock
Expanding Au
Maxwellian DT core
Expanding DT-CH
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“Conventional” chamber simulations
• For low Xe pressure the gas volumetrically heats, there is little hydrodynamic motion– 50-50% split between plasma deposition and
wall deposition for target debris at 50 mTorr.• The wall temperature response is most
sensitive to ion stopping models and Xe opacity in 10-1,000 eV range.– Ion stopping model determines prompt heat input– Opacity determines gas re-radiation time
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BUCKY explosion simulations160 MJ NRL Target Ionic Debris Deposition in 50 mTorr Xe
-5
0
5
10
15
20
25
0 1000 2000 3000 4000 5000
Time (ns)
Ene
rgy
depo
site
d (M
J)
Plasma(MJ)
Wall(MJ)
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Summary
• New debris transport model developed and working. Next step:– Review ion-stopping model and opacity theory– Do simulations
• Spartan initial conditions• Xe vs. Ar
• Bounding calculations– Pure hydrodynamic calculation working– Kinetic calculation in progress– Next step: Evaluate HANE literature