on the pulsed fission fusion propulsion concept€¦ · initial pulsed nozzle model • test...

Marshall Space Flight CenterNational Aeronautics and Space Administration

Progress on the Pulsed Fission‐Fusion Propulsion System Concept

Robert B. Adams, Ph.D.ER24/Propulsion Research and Technology BranchGeorge C. Marshall Space Flight CenterNational Aeronautics and Space Administration

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Jason Cassibry, Ph.D., Kevin SchilloPropulsion Research CenterDepartment of Mechanical and Aerospace EngineeringUniversity of Alabama in Huntsville

https://ntrs.nasa.gov/search.jsp?R=20140008798 2020-06-09T10:14:47+00:00Z

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PuFF Concept

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Introduction to PuFF

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Magneticnozzle coils

Magneticfield lines

Lithium linerand radiation 

shield

Cathode

D‐T fuel

UF6 fuel

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Operation of a Z Pinch

Anode

ICathode

Vaporized Wire Array

Plasma Cylinder

Evacuated Chamber

B, Magnetic Flux

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DT FRC TargetPlasma

Fissionableliner

Axial and Radial Thermal conduction

Fusion heating power

Bremmstrahlung and Cyclotron Radiation

MagneticField Lines

Fissionheating power

Neutron inducedFast fission reactions

Fission/DT FRC Fusion TargetLoss Mechanisms included in ModelHeating Mechanisms Included in Model

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Fusion Power Balance

• Parameter space for ignition

• Greatly broadened with embedded magnetic field

• Marginally improved with 6Li and thorium liners

• Significantly enhanced with uranium liners (235U and 238U)

Synchrotron Radiation Dominates

Fission Power Dominates as Neutron Count

Becomes Significant

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Parameters within net Power Increase

Choose  R = 10‐5 at 15 keV. Let R = 1 mm, thickness of uranium liner is 5 mm, length of target is 2 cm Density of DT target is  0.1 kg/m3

Total energy in DT target is only ~5 kJ, 1% of Charger 1 stored energy

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• Solve with Smooth Particle Electromagnetic Variant of Finite-Difference Time Domain (FDTD) method

• FDTD well documented, highly accurate grid-based method for analyzing the time evolution of electric and magnetic fields, utilized in PIC codes

• Can interpolate charged fluid particles to grid to model conductivity or charge and current density

Maxwell’s Equations

• Solve with Smooth Particle Hydrodynamics (SPH)• Gridless Lagrangian technique• Vacuum/plasma boundary well defined• Leverage same engine as Maxwell Equation Solver

Multifluid Equations of Motions

Both methods yield to ‘vectorized’ coding, making multiprocessor (parallel) computing easy

Our Approach:  Solve Maxwell's Equations Coupled to Multifluid (Ions, Electrons, Neutrals) Equations of Motion

Marshall Space Flight CenterWhat is SPH? 

Numerical method for approximating probability densities over a domain of particles.

Developed initially to model stars by Monaghan, et al, in 1977. Currently used mostly in hydrodynamic modeling and CG effects in 

film and video games.

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How does SPH work?

Integral interpolant:

I , d ′

A – quantity measured (density, temperature, etc.)W – differentiable kernel functiondr‘ – volume differentialh – smoothing length.

Summation over mass elements:

s ,

Similar to density probability calculations.How quantities are accurately calculated with a small particle domain.

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Run SPFMax

define_constants

read_input Input file?

Yes

No

run (inputfile)

input_default

set_item_defaults

define_geometryitem(ii)

GMSH?

Yes

No

load_gmsh2(filename)

define_particles

set_default_if_needed

define_static_particles

define_electromagnetic_particles

define_physics_models

define_circuit_models get_circuit_particles

define_equations_of_motion

define_numerics

run_sph_solver

Maxwell_equations

circuit

set_input_defaults

check_for_material_database

set_matter_defaults

‘brick’

isstatic?Maxwell?

emcount + 1

last_block= ‘vacuum’last_block= ‘vacuum’

Yes

set_matter_defaults

set_default_if_needed

particle

isstatic?

Yes

No

Maxwell?

Yesinpolyhedron

NoNo

initialize_thermodynamic_state

amperes_law

circuit_rlc

circuit_constant

faradays_law

hydro_Lorentz

RK1

em_leapfrog

kernel_cubicspline

hydro

motion

continuity

Marshall Space Flight CenterNational Aeronautics and Space Administration

_ p _run_sph_solver

While notdonep _ _ pupdate_time_step

Maxwell?

Yes

p _ pupdate_emparticles

No

time = time +dtelectric_particle_ time_integrationelectric_particle_ time_integration

Yes

particle_time_integration

particle_time_integration

No

hydro

_ p _save_output_data

update_emparticles

Yes

No

p _pupdate_particles

save_output_data

export_to_cassplot

output_initialize_variables

Plot data

Yes

g _ p_neighbor_lookup_rh

get_local_electromagnetic_fields

vab

eos p _pupdate_particles

obj.nbrs

obj.r

g _ p_ pneighbor_lookup_spacial

obj.nbrs_mutual

obj.r_mutual

Maxwell?

Maxwell?

YesNo

get_magnetic_neighbors_for_electric

get_electric_neighbors_for_magnetic

get_fluid_neighbors_for_electric

get_electromagnetic_transport

g _ _ y _ _ _get_static_hydro_bcs_for_fluid

g _ _ _ _get_wall_bcs_for_fluid

p _pplot_particles

set_cell_index_geometry_parameters

_ pset_cell_index_geometry_parameters

_spatial

update_staticparticles

isstatic?Yes

No

_ pkernel_cubicspline

Else

isstatic?Yes_ _ pkernel_mutual_cubicspline

spline(p,ep)kernel_mutual_cubic-

spline(p,ep)

spline(p,mp)kernel_mutual_cubic-

spline(p,mp)

No

If 0isstatic? Yes

Yes

isstatic?

Yes

Else g _ _get_vacuum_nodes

get_fluid_neighbors_for_electric

g _ _ _ _get_wall_bcs_for_fluid

Maxwell?

isstatic?

Else

update_staticparticles Yes

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Equations of motion (planned)Equations of motion (completed)

Transport effects,which can be basedon nonequilibrium

distribution functions(kappa and power law)

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Initial Pulsed Nozzle Model

• Test thermal expansion of gas nozzle with various initial conditions

• Nozzle geometry• Gas

• Temperature• Density• Radius• Length• Composition

• Lays ground work and expectations for magnetic nozzle

Nozzle wall

Initial gas from z-pinch

Direction of motion

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Preliminary results

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Preliminary results

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Preliminary results

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Preliminary results

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Preliminary results

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NIAC Phase I Goals

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Crewed Mars Mission Concept

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Marshall Space Flight Center

Mission Concepts

Mars 90 Mars 30 Jupiter 550 AU

Outbound Trip Time (days) 90.2 39.5 456.8 12936Return Trip Time (days) 87.4 33.1 521.8 n/aTotal Burn Time (days) 5.0 20.2 6.7 11.2Propellant Burned (mT) 86.3 350.4 115.7 194.4Equivalent DV (km/s) 27.5 93.2 36.1 57.2

22Figure 3 Mars 90 Day Transfer Trajectories

Mars OrbitEarth OrbitTransfer Traj OrbitTransfer Trajectory

Mars OrbitEarth OrbitTransfer Traj OrbitTransfer Trajectory Polsgrove, T. et al. Design of Z‐Pinch and Dense 

Plasma Focus Powered Vehicles, 2010 AIAA Aerospace Sciences Meeting

• Engine• Isp = 19,400 sec• T = 38 kN• 10 Hz pulse freq.

• Vehicle• Mdry = 552 mT• Mpay = 150 mT• 30% MGA

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Mating SPFMaX and MCNP

SPFMax gives• Ability to model 3d effects• Can propagate magnetic fields in vacuum• Easily editable

MCNP• Track neutron life, fission reactions• Flexible geometries

Second half of NIAC is to run codes concurrently• synchronize neutron population vs. time• Optimize energy output

- As function of geometry- As function of composition

– Mix of UF6, D‐T– Lithium liner thicknesses

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• Gasdynamic nozzle performance to be compared with magnetic nozzle to assess loss mechanisms in magnetic nozzles, e.g.

• Field/plasma instabilities

• Plasma detachment

Direction of current

Single turn Magnetic Nozzle

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NIAC Phase II Experimental Options

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Charger ‐ 1

A test facility for high power and thermonuclear fusion propulsion concepts, astrophysics modeling, radiation physics

Located in the UAH AerophysicsLab at Redstone

The highest instantaneous pulsed power facility in academia – 572 kJ (1 TW at 100 ns)

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Experimental Roadpath

Methodology• Incremental improvements in experimental capability• Benchmark model with experimental data• Can also run any experiments below with lower power systems• Looking for comments and suggestions here!

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Li wire DeuteratedPolyethylene

D‐D slushD‐T slushSolid U238

D‐Li solidSolid U238

Implosion Neutronflux

Plasmastability

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Long Range Plans

Charger II• Construct breadboard PuFF system capable of 10‐20 Hz operation

- Upgrade to flight weight hardware – NASA- Optimize pulse for maximum power output – DOE- Astrodynamics, radiation protection, other research goals ‐ Various

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