Investigation of Energy-Scaling of Thrust Performance for Laser Fusion Rocket

A laser fusion rocket has been proposed for interplanetary flight. This rocket generates a high-energy plasma via laser-fusion and expels it via a magnetic nozzle. The magnetic nozzle is a key component for the rocket performance, and we have investigated the impulse bit generated from the magnetic nozzle by using simulations and experiments in relatively low energy regime of a few joules. In addition, the energy dependence on the thrust performance is an essential factor to evaluate and design the laser fusion rocket. Here, we conducted numerical simulations in energy regimes from a few joules to mega joules to understand the thrust performance both for small-scale experiments and for full-scale fusion rockets. We find that the momentum efficiency does not depend on the propellant mass, material, and plasma energies, and the impulse bit is expressed as the power-law of the plasma energy and mass. These relations are important for designing missions and for estimating the thrust of fusion rockets.