Target threat spectra

Gregory Moses and John SantariusFusion Technology Institute

University of Wisconsin-Madison

HAPL Review MeetingMarch 3-4, 2005

Naval Research LabWashington DC

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

“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

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

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.

Bounding threat spectra calculations High collisionality – pure hydrodynamic

Bounding threat spectra calculations High collisionality – pure hydrodynamic

Bounding threat spectra calculations High collisionality – pure hydrodynamic

4x108 cm/s

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.

• 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

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

“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

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)

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