James Benford presents his Ultrahigh Acceleration Neutral Particle Beam-Driven Sails at Space Access 2019.
The Neutral Particle Beam-Driven Sails could enable an interstellar probe to alpha centauri that would be 1000 times larger and 60% of the speed of the current Starshot laser-driven proposal.
James goes over the engineering for a 1 kg probe that can be sent to a nearby star in about seventy years using neutral beam propulsion and a magnetic sail. The concept has been challenged because the beam diameter was too large, due to inherent divergence, so that most of the beam would miss the sail. Increasing the acceleration from 1000 g’s to 100,000 g’s along with reducing the final speed from 10% of lightspeed to 6% of lightspeed solves the issue of accelerating before the beam spreads too much.
They would start with lower speed systems, lower mass Magsails for faster missions in the inner solar system. As the system grows, the neutral beam System grows and technology improves. Economies of scale lead to faster missions with larger payloads. As interplanetary commerce begins to develop, making commerce operate efficiently, outcompeting the long transit times of rockets between the planets and asteroids, the System evolves.
MagSail is a huge ring of superconducting wire attached to a space vehicle.
Benford is using a neutral particle beam to propel the magsail.
Drift Tube Linac drift rube regions separated by acceleration regions. There are many linac accelerators.
Rocket launched BEAR (Beam Experiment aboard a rocket) was launched 30 years ago. A neutral particle beam generator was actually deployed and operated in space and its performance was measured. On July 13, 1989 the Beam Experiment Aboard Rocket (BEAR) linear accelerator was successfully launched and operated in space by Los Alamos National Laboratory.
The neutral particle beam approach is conceptually similar to photon beams such as the laser-driven Starshot project. A disadvantage of reflecting photons from the sail will be that they carry away much of the energy because they exchange only momentum with the sail. Neutral particle beams transfer energy, which is much more efficient. The reflecting particles may in principle be left unmoving in space after reflection and thus the efficient energy efficiency can approach 100%.
The thrust per watt beam power is maximized when the particle velocity is twice the spacecraft velocity. The Magsail, with a hoop force from the magnetic field, is an ideal structure because it is under tension. High-strength low-density fibers make this lightweight system capable of handling large forces from high accelerations. The rapidly moving magnetic field of the Magsail, seen in the frame of the beam as an electric field, ionizes the incoming neutral beam particles.
Since beam divergence is fundamentally limited, high accelerations can be used to insure the sail will stay within the beam until it reaches the desired final velocity, even with microradian divergence. This leads to ultrahigh, 100,000 g’s, 1 million m/s2 to accelerate to 0.06 c. The Starshot system, a laser beam-driven 1 gram sail with the goal of reaching 0.2c, has been quantified in a detailed system model by Kevin Parkin. It too uses 100000-1 million g’s. Magsail-beam interaction remains an aspect of this concept that needs further study, probably by simulations.