November 8, 2023 by Brian Wang
Jeff Greason proposes extending power beaming using the magnetic pinch phenomenon. The quasar 3C273 produces a plasma jet that is 100,000 light years long. This distance would span the Milky Way. It may be possible for humans to produce pinched relativistic electron jets over the much smaller distances needed to propel a spacecraft out of the Solar System. Charged beams in a low-density plasma can confine themselves over long distances. The beams carrying a current creates a circular axial magnetic field which in turn confines the beam. Pinching is a means of self-confinement of the beam that has been studied since the 1930s. A pinch forming a jet explains why solar proton events can strike the Earth despite the 1 AU distance, and why galaxy-spanning jets like that in the image above can form.
The extended beam could strike a plasma-filled waveguide which can couple to backwards plasma wave modes. This effect would launch plasma in the opposite direction as reaction mass. This keys to existing work on plasma accelerators (so-called “wakefield” accelerators), which use similar physics. We would need experiments to explore how much beamed energy can be returned in this way.
If we can increase the range of a beam from 0.1 AU to 1000 AU, this means we could send much larger spacecraft. The spacecraft could be 100,000 times larger, at the same power levels. The one gram-sized spacecraft proposed by Breakthrough Starshot’s laser methods could become 10 kilograms. The acceleration time from minutes to months. That increased payload size is particularly useful when it allows a braking system aboard for long-term study of the target.