October 24, 2016

Positron Dynamics Vision of Antimatter Catalyzed Fusion

A few days ago Nextbigfuture interviewed Ryan Weed of Positron Dynamics and in 2015there was a youtube video which Ryan Weed had explained their antimatter fusion propulsion effort.

Ryan had two later videos. One for Wired and one for TEDx.

Reviewing the videos based on information from Ryan Weed.

* 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
* could enable 1G acceleration and deceleration propulsion which would 3.5 weeks to Pluto














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