Propelx is still raising the $1.5 million bridge round for Positron Dynamics. It is over 80% raised. Accredited investors can still contribute to Positron Dynamics.
Positron Dynamics is developing antimatter propulsion for spacecraft. They are working towards nearterm propulsion for cubesats.
* 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
Positron Dynamics working towards fusion catalyzed deuterium propulsion
Last year the Positron Dynamics plan was to fly an antimatter cubesat in 2019 and they are still on track towards that goal.
Sodium (22Na) emits a proton makes a beta decay which then generates positron Sodium 22 has a half-life of 2.605 years.
Abstract of Positron Dynamics Patent Apparatuses and methods for the moderation of positrons are provided herein. The apparatus may include a structure consisting of linear arrays of electrode and semiconductor structures of generally planar or cylindrical form with vacuum gaps between each element electrode. This structure may be contained within a vacuum chamber. The positron source may be positioned adjacent to the moderator structure or the electrodes may act as the positron source by pair production through bombardment of high energy photons, electrons, or neutrons. Positrons from this source may be implanted into the moderator material and drift to the moderator surfaces through the influence of the electric fields produced by the electrodes. Positrons may be emitted from the surfaces of the moderator material and may be confined by orthogonal electric and magnetic fields while they drift out from the vacuum gap between cathodes and anodes for extraction.
Currently, the most intense source of positrons in the world produces 10^9 cold positrons per second. At this production rate, it would take over 10 million years to accumulate a milligram of positrons. In order to realize these newer concepts, a much more intense source of positrons must be developed.
They have worked on the seimconductor structures to moderate the positrons and slow them down and enable useful work to be performed with it.
They have a pulsed laser and are analyzing the positrons.
After the cubesat proves the useful propulsion from the antimatter system and is used to generate a commercial revenue stream,
the initial cubesat propulsion will have low power levels but will have ISP of 100,000 to 1 million.
This will be superior to existing and planned ion drive propulsion.
NASA HiPEP (ion drive) system has 9600 (+/- 200) seconds of specific impulse. Australian lab work on the Neumann ion Drive has ISP as high as 14,690 (+/- 2000), with even conservative results performing well above NASA’s best. That suggests the drive is using fuel far more efficiently, allowing for it to operate for longer. Furthermore NASA’s HiPEP runs on Xenon gas, while the Neumann Drive can be powered on a number of different metals, the most efficient tested so far being magnesium. Ion drives only have a few tens of micronewtons per watt of propulsive force.
The positron catalyzed fusion will have superior newtons per kw.
The path forward is to use regenerative (breeding) of isotopes that emit more protons for positron emissions. This regenerative approach will enable full scale antimatter catalyzed deuterium fusion propulsion. The Deuterium fusion propulsion will be able to achieve performance like other deuterium fusion rocket designs which is up to 10% of lightspeed and 100,000+ ISP to millions of ISP
Deuterium fusion also has the advantage that rockets can refuel with Deuterium by simply putting a heated wire into a mostly water ice asteroid and getting more water which will have some deuterium.
Storing Antimatter has simulations but still needs work so Positron Dynamics is working to propulsion that requires no antimatter storage
The linear accelerator plan has been deferred because the higher cost and the challenges of storing antimatter.
There is work at Washington state university to store antimatter in microtraps. In 2014, a paper described rogress toward a novel microtrap array with large length to radius aspect ratios and radii of the order of tens of microns. The proposed design consists of microtraps with substantially lower barrier potentials than conventional Penning-Malmberg traps arranged in parallel within a single magnet. Simulations showed positron plasma with 1E10 cm-3 density evolves toward a rigid-rotation phase in each microtrap while 10 V barriers confined the plasma axially. A trap of 4 cm length including more than 20,000 microtubes with 50 micron radii was fabricated and tested. Experiments conducted with electrons in a test structure addressing each microtube with a narrow beam will be described. This will explore the basic physics of the microtraps. Observed results were promising and they open a new avenue for manipulating high-density non-neutral plasmas.
Simulation demonstrated each microtrap with 50 micron radius immersed in a 7 Tesla magnetic field could store positrons indefinitely with a density of 160 billion per cubic centimeter while the confinement voltage was only 10 Volts. For microtraps with radii between 100 micron and 3 microns, the particle density scaled as radius^-2. Plasma confinement time was also independent of trap length. A unique approach for the fabrication of long-aspect ratio microtubes was presented for 100 micron microtraps
SOURCES -Wikipedia, CERN, Washington State University, US Patents, Interview Ryan Weed of Positron Dynamics, youtube videos, Propelx
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