Solutions for near-term antimatter fusion propulsion using isotope breeding cycle

The world only produces a nanogram of antimatter every year but we cannot store any of it for any length of time.

Positron Dynamics has solutions to all of the huge problems to use the immense power of antimatter.

Positrons are 2000 times easier to produce than antiprotons. The positron or antielectron is the antiparticle or the antimatter counterpart of the electron.

Positrons are produced constantly from various isotopes. Isotopes are variants of a particular chemical element which differ in neutron number.

They get around the problem of generating and storing antimatter by breeding Krypton 79 isotope to constantly generate more and more positrons.

They will breed Krypton 78 to Krypton 79 by capturing neutrons from D-D fusion. Deuterium is one of two stable isotopes of hydrogen.

Surround a source of D-D fusion with 1 meter thick ten atmospheric pressure Krypton 78 gas will capture almost all of the neutrons from D-D fusion.

The D-D fusion will be triggered using positrons. Thus the positron triggers the fusion which produces neutrons to breed more isotope, the isotope produces the positrons.

NASA has provided funding for Positron Dynamics with a Phase I NASA Innovative Advanced Concepts study.

100 micrograms of Krypton 79 can the start and in 3-4 months, the 10 kilograms of Krypton 78 would breed to Krypton 79. This would be able a proposed system to produce 60 newtons of thrust. This would enable the system of antimattered trigger fusion to propel a spacecraft to about 10% of the speed of light and enable a 50 year trip time to Proxima Centauri.

The fuel breeding cycle is shown above.

Krypton isotopes to generate hot positrons.
Use their system to moderate the positrons so they can be used.

They need to efficiently create more isotope to get more positrons instead of using magnetic storage.

Details of how the positron triggered fusion reaction produces thrust

Diverting, or directing, the trapped energy from the annihilation process to propel the rocket. To achieve this, Weed, CEO of Positron Dynamics, and his team use fusion reactions to transfer the kinetic energy of the gamma-ray producing positron beam into charged particles. Because charged particles “like” to follow magnetic field lines, Weed and his team employ magnets to direct the energy and produce the holy grail of thrust.

Timelines and the Future

Positron Dynamics proposed milestones which have had some slippage:

— Laboratory demonstration of “scalable” thrust using positrons. Six to eight months.

— Positron-powered launch of small “cubesat” satellite into low-Earth orbit, demonstrating orbital change from positron propulsion. Eighteen months to two years.

This propulsion system could be used in satellite constellations, for example — as part of a global network of broad-band internet, enabling virtually anyone on the planet access to the internet.

— Launch of another rocket to further demonstrate the feasibility of positrons to power a spacecraft. Two-and-a-half years (probably followed by a succession of other unmanned spacecraft over a period of years).

— Launch of a positron-propelled spacecraft to Mars. In the 2030s.

Degrading materials limits the scaling of the propulsion system.

Previous discussion of cubesat demonstration and Sodium 22 isotope

* Sodium 22 isotope (which they get in liquid form) will produce positrons which will be moderated with semiconductor structures

Liquid Sodium 22

The Moderator structure

Cold positrons instead of 1 million times hotter than the sun

* moderated cold positrons produced in a gamma ray beam
* The beam hits the dense film of deuterium which produces fusion products
* the fusion products are now charged particles which can be then guided as propulsive thrust with magnets

positron emission: ²²Na → ²²Ne + 1 e⁺ + 0.94 MeV of kinetic energy
positron annihilation: e⁺ + matter → pion (5%) or kaon (95%)
kaon decay: kaon → muon (80%) in 20 nsec
muon capture: muon + D or T → mD or mT
fusion (1): mD + T → ⁴He + ¹n + muon (non-consumed) (0.01 – 0.1 nsec)
fusion (2): mT + D → ⁴He + ¹n + muon (non-consumed) (0.01 – 0.1 nsec)
fusion (3): mD + D → ³He + ¹n + muon (non-consumed) (0.07 – 1.5 nsec)
muon decay: muon + time → electron + neutrinos (2,200 nsec)

²²Na (sodium missing one neutron) is almost perfect. Halflife of 2.6 years.

Each gram of the stuff:

1 g • ( 6.023×10²³ atom/mol ÷ 22 AMU ) = 2.74×10²² atoms per gram
= 434,400,000,000,000 decays per second.
× 1.6×10⁻¹⁹ J/eV × 1,000,000 eV/MeV × 2.843 MeV/decay
= 197 joules per gram

Muon Catalyzed Fusion

Muons are unstable subatomic particles. They are similar to electrons, but are about 207 times more massive.

The α-sticking problem is the approximately 1% probability of the muon “sticking” to the alpha particle that results from deuteron-triton nuclear fusion, thereby effectively removing the muon from the muon-catalysis process altogether. Recent measurements seem to point to more encouraging values for the α-sticking probability, finding the α-sticking probability to be about 0.5% (or perhaps even about 0.4% or 0.3%), which could mean as many as about 200 (or perhaps even about 250 or about 333) muon-catalyzed d-t fusions per muon. Indeed, the team led by Steven E. Jones achieved 150 d-t fusions per muon (average) at the Los Alamos Meson Physics Facility. Unfortunately, 200 (or 250 or even 333) muon-catalyzed d-t fusions per muon is still not enough to reach break-even. Even with break-even, the conversion efficiency from thermal energy to electrical energy is only about 40% or so, further limiting viability.

However Muon Catalyzed fusion from antimatter would multiply the energy production from the antimatter.

Each muon catalyzing d-d muon-catalyzed fusion reactions in pure deuterium is only able to catalyze about one-tenth of the number of d-t muon-catalyzed fusion reactions that each muon is able to catalyze in a mixture of equal amounts of deuterium and tritium, and each d-d fusion only yields about one-fifth of the yield of each d-t fusion, thereby making the prospects for useful energy release from d-d muon-catalyzed fusion at least 50 times worse than the already dim prospects for useful energy release from d-t muon-catalyzed fusion.

However, Positron Dynamics is looking at the fusion for propulsion and not energy production. The fusion rate for d-d muon-catalyzed fusion has been estimated to be only about 1% of the fusion rate for d-t muon-catalyzed fusion, but this still gives about one d-d nuclear fusion every 10 to 100 picoseconds or so

Description of a pellet based antimatter catalyzed fusion system but gives an idea of performance based on percent of material that is fused

* the 6U cubesat that they will use to test the propulsion in space will be generating 100s of watts
* the propulsion will have delta V of 1 to 10 km/second
* Later systems will have more delta V and enable cubesats and small satellites to stay in orbit for years instead of days

* the cubesats with propulsion will enable very low orbit internet satellites

* in the 2020s if things go well they will be able to scale to 10 km/second to 100 km/second with 10-100 kilogram payloads for small probe exploration of the solar system
* Later beyond 2030, they will have regenerative isotopes for a lot more power and achieve ten million ISP and several kilonewtons of propulsive force. This would seem to require multiple propulsion units as the more recent discussion limited propulsion to 60 newtons.
* could enable 1G acceleration and deceleration propulsion which would 3.5 weeks to Pluto

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