Future of Antiproton Triggered Fusion Propulsion Brice Cassenti & Terry Kammash University of Connecticut & University of Michigan

Future of Antiproton Triggered Fusion Propulsion Propulsion Concepts Nuclear Reactions Challenges –Lithium-6 fuel –Ablation radiation shield –Antiproton trigger scattering

Inertial Confinement Fusion Propulsion Concepts Critical Mass Systems External Compression Systems Antiproton Triggered Systems MICF Hybrid Pellets Hybrid Fission-Fusion Pellets

Orion From Martin and Bond, JBIS

Courtesy of G. Smith

Nuclear Reactions DT Fusion Reaction Uranium Fission Lithium Fission

Fusion Reactions The DT reaction And Lithium fission reaction Are equivalent to

Thermonuclear Weapon

Antiproton Annihilation Reactions Antiproton-Proton Annihilation Antiproton-Neutron Annihilation Antiproton-Uranium Annihilation

Some Technical Challenges Compression Driver Cryogenic Storage Neutron Radiation Absorption & Heat Rejection Ignition

MICF Laser Pellet Ignition

MICF Antiproton Pellet Ignition

Antiproton Triggered MICF Ignition

Antiproton Triggered MICF Pellet

MICF Transient Magnetic Fields Magnetic field intensities depend critically on spot size.

Antiproton Dispersion

Antiproton Dispersion Effects Annihilation Scattering Energy deposition

Annihilation Approximations

Scattering Particle physics approximations – – Monte-Carlo simulations

Energy Deposition

Monte-Carlo Simulations Two layers: fusion fuel & uranium Each layer divided into 50 intervals Updated antiproton direction, coordinates and energy Ten thousand simulations per case Final beam radius set to final antiproton position standard deviation Spread angle set to 90 degrees.

Simulation Results

Antiproton Dispersion Conclusions Antiprotons: -Are a high energy density storage mechanism. -Can be used to initiate a fission reaction -Magnetic field strength depends on scattering -Beam energy at minimum of fusion fuel spectrum Need experiments to measure transmission spectra for antiprotons for low energy antiproton beams. Specific impulse well in excess of 50,000 seconds and high thrust-to-mass ratios are possible.

Tritium Fuel Considerations Tritium is naturally radioactive –Beta decay –Half-life ~12 years Tritium requires cryogenic storage Lithium-6 is not radioactive Lithium-6 does not require cryogenic storage

Deuterium-Tritium Pellet Construction

Lithium-Deuteride Pellet Construction

Pellet Discretization

Compression Simulation Momentum Conservation Mass Conservation Constitutive Law p=p(  )

Initial & Boundary Conditions No initial displacements or velocities Center velocity is zero Outer pressure is zero Explosive temperature found from energy Explosive pressure from gas law

Neutron Interactions Scattering Fission –Uranium and Lithium Cross sections Mean free path – =1/  n

Pellet Geometry

Material Properties

Nuclear Properties Determine Pellet Size

Internal Tamper

Lithium Fuel Conclusions Advantages: –Produces charged particles –Is not radioactive –Is solid at room temperature Disadvantages: –May require external compression –Will produce high energy neutrons

Hybrid Fusion-Fission Nuclear Pulse Propulsion Use of Li 6 –Reduces tritium handling problems –Decreases specific impulse System can be developed in a two step process –Use fusion to boost the specific impulse of a pulse fission rocket –Evolve to a full hybrid system

Ablative Shield Model Heat added from neutron absorption Heat transfer by conduction and radiation Heat lost through ablation –Moving coordinate system –Ablation velocity used

Ablation Model q vsvs Q Heat lost by radiation and ablation Surface recession velocity Neutron heat added

One Dimensional Ablation Model Heat Source: Heat Conduction: Boundary Conditions: — Attemperature is at ambient — At x=0 temperature is at sublimation — At x=0:

Ablation Model Solution Surface Recession Velocity: Temperature distribution:

One Sided Radiation Model Heat Source: Heat Conduction: Boundary Conditions: — Attemperature is at ambient — At x=0

One Sided Radiation Solution Surface Recession Velocity: Temperature distribution:

Two Sided Radiation Model Heat Source: Heat Conduction: Boundary Conditions: — At — At x=0

Two Sided Radiation Solution Surface Recession Velocity: Temperature distribution: Two boundary conditions relate C 1 and C 2 Arbitrary constants are solved for iteratively Solution is checked numerically

Material Properties for Shield

Neutron Heating and Ablation Response Parameters

Carbon Radiation Shield

Ablation Conclusions Carbon shield may work without ablation Temperature is a maximum between the surfaces Ablation will begin at maximum temperature location Ablation will not be steady

Typical Pellet Geometry Core radius0.05 mm Fuel Radius1.00 cm Tungsten Shell Thickness0.10 mm Antiproton Beam Radius0.10  m Uranium Hemisphere Radius0.30 mm

Typical Pellet Performance Antiproton Pulse2x10 13 for 30 ns Maximum Field24 MG Pellet Mass3.5 g Specific Impulse –600,000 s for 100% fusion –200,000 s for 10% fusion

MICF Propulsion Parameters –200,000 seconds specific impulse –138 pellets per second –Mass ratio fixed to 1.5 for one-way missions Missions –7 day trip to Mars: acceleration limited –30 day trip to Jupiter: specific impulse limited –180 day trip to Pluto: specific impulse limited

Promise of ICF Propulsion ICAN-II: 13,500 seconds specific impulse –30 days to Mars –90 day trip to Jupiter –3 year trip to Pluto MICF: 200,000 seconds specific impulse –7 days to Mars –30 days to Jupiter –180 days to Pluto

Antiproton Triggered Fusion Propulsion Conclusions Technical challenges –DT cryogenic storage –Pellet compression –Neutron radiation damage Solutions –Lithium fuel –Tampers and explosives –Non-ablating carbon shield

Future Work Complete accurate simulations –Ignition –Fusion propagation –Neutron generation Borrow weapon design ideas –Compression using heating and inertia –Fusion boosted fission Determine Transmission Spectra