Fusion and Antimatter: A Hybrid Approach to Reaching 0.1c

Author: Ryan Weed, PhD, Founder, Positron Dynamics Inc

Abstract Background: The incredible energy density of antimatter is the key to exploration beyond our solar system. When antimatter annihilates with matter, it releases an amount of energy equal to the rest mass of both particles. This results in a specific energy of 90MJ/ug, the highest known specific energy of any process. Since the prediction and discovery of antimatter in the 1920’s and 1930’s, its’ use as an energy source for rocket propulsion has been considered in many forms but has yet to be demonstrated. The key difficulties have been:

1. Trapping large amounts of antimatter
2. Directing the annihilation energy to produce thrust.

To solve these problems, our research has focused on radioisotope sources of positrons, utilizing the annihilation energy to catalyze fusion reactions. This hybrid antimatter/fusion approach avoids the problems associated with trapping antimatter through the use of a radioisotope antimatter source, while maintaining the ability to guide the fusion reaction products to produce thrust at very high specific impulse (>100,000 s).

Abstract Objectives: Key technical questions that this research addresses to determine feasibility:

1. Is fusion fuel ignition achievable using radioisotope based pulsed positron source?
2. Can the required positron source, accumulator and charged particle pulsing ion optics be integrated into Size, Weight and Power envelope of a spacecraft, while maintaining reasonable propulsion performance metrics?
3. Will the propulsion system benefit a proposed mission supplication (Interstellar transit)?

Abstract Methods: The research team utilized a custom 0-D Energy balance model and 2-D PIC code to determine annihilation catalyzed microfusion ignition requirements. In addition, Monte-Carlo neutron propagation (MCNP), PENELOPE, and SIMION codes were used to model the fuel cycle, positron fuel implantation, and beam optics to determine propulsion system properties.

Abstract Results: Ignition modeling results indicate that fast ignition can be achieved using a realistic number of pulsed positrons with standard temporal and spatial compression techniques. Neutron propagation simulations show that fusion neutrons can be thermalized and efficiently captured to produce positron emitting radioisotope (Kr-79). Mass properties of the required subsystem lead to a minimum spacecraft mass of approximately 1,000kg at 100km/s delta-V, with prospects for scaling to much larger mass and delta-V capability.

TRL Assessment: Currently, antimatter annihilation catalyzed fusion propulsion is a concept that has been formulated and analyzed inliterature. In addition, the feasibility of the propulsion system was recently documented in a Phase I NIAC Report. Thus, we assign the current TRL as (3).

Abstract Development:
2020-2022: Use existing neutron generators and pulsed positron facilities to demonstrate 79Kr enrichment and microfusion ignition, respectively.
2022-2025: Combined fuel cycle ground demonstration
>2025: Vacuum thrust measurement

Abstract Near-Term Technical Milestones:

1. Predictable and reproducible dense Deuterium production on fuel substrate.
2. Use PIC microfusion modeling to optimize target design for mission application (Isp/Thrust)
3. Develop ignition test bed for fusion yield demonstration at existing positron facility
4. Demonstrate Kr radioisotope enrichment and positron beam production using existing DD neutron generator and natural Kr isotopes.
5. Use PIC microfusion modeling to optimize target design for mission application (Isp/Thrust)
6. Develop ignition test bed for fusion yield demonstration at existing positron facility
7. Demonstrate Kr radioisotope enrichment and positron beam production using existing DD neutron generator and natural Kr isotopes.

Abstract Conclusions: In conclusion, initial feasibility of performance capability has been demonstrated using the realistic physics based modeling and constraints. We also present a path forward towards the first vacuum thrust measurement of an antimatter/fusion hybrid propulsion system. Such a propulsion system would have broad applicability beyond interstellar transit missions (e.g. planetary defense, asteroid capture, constellation servicing).