Solar wind nozzle acceleration for space flight (mega project)

[gpeabody]

Hi folks, I've been daydreaming about space travel again, and an idea has come my way. It's probably unworkable, but I know next to nothing about fluid dynamics, so I would love to hear your thoughts.

Two of my favorite forms of proposed space travel are the magnetic and electric sails. The idea behind them is to basically form a big effective parachute using either electrostatic forces from a grid of positively charged wires (the electric sail), or from a magnetic field due to a current circulating in a wire loop. The electric or magnetic fields interact with incoming charged particles and create drag, causing the spacecraft to accelerate towards rest with respect to the moving charged particles (so a spacecraft in the depths of interstellar space could deploy such a sail to brake, or a spacecraft in our solar system could deploy it to accelerate away from the sun, up to the velocity of the solar wind). They sound like clever, elegant solutions which are almost passive (it would take some energy to maintain the charge on an electric sail or the current in a magnetic sail, but you don't have to directly supply energy to convert it into kinetic energy). The electric sail, in particular, has received some attention recently as a potentially economic mode of in-solar-system journeys.

It would be awesome if these could be used to launch probes from within our solar system for interstellar travel, but unfortunately the velocities are just too low. The solar wind is ~300 km/s or 0.1% the speed of light, and this represents the maximum possible velocity for these passive sails accelerated by our solar wind (ok, the solar wind can be a bit faster in certain places and at certain times, but not by orders of magnitude). If the speed limit were 10x higher we might be able to consider these passive sails for long-term multi generational projects. If it were 100x higher they could be useful for projects designed for a single human lifetime.

So I was wondering, would it be possible to speed up the solar wind? The solar wind is just a plasma/fluid, (one that is highly compressible and supersonic if I understand correctly), and nozzles are exactly the kind of thing designed to alter flow properties like velocity. The idea would be to construct a gargantuan nozzle in space, pointing radially away from the sun (see attached figure for illustration). The nozzle would be made from simple loops of wire floating in space and spinning to provide tension. The loops could either be charged to create an electrostatic nozzle, or carrying current to make a magnetic nozzle. While the scale of the nozzle might be immense, perhaps thousands of kilometers, the mass of these wire loops could still be relatively small ('relative' ie, maybe a few good asteroid mining operation hauls). The geometry of the nozzle would be designed so that the exiting particles are traveling much faster (ideally 10x their initial velocity or more).

From what I know about nozzles (ok, what I googled over the last couple days) if the fluid is compressible and supersonic, the nozzle should be divergent, with the solar wind entering on the narrow end and exiting from the wide end. The exiting flow will be faster, but also lower density (and therefore more difficult to extract thrust from, but with a higher upper speed limit). Is that correct? Would there be any way to increase the velocity without decreasing the density, possibly by using a convergent-divergent nozzle?

The main question I have about this idea, is how far would the stream of accelerated solar wind particles persist? Would they just totally mix and equilibrate with the surrounding solar wind, eliminating the high speed solar wind corridor after a few tens of kilometers? Or could it be designed to persist over a few astronomical units? Does this depend on the width of the nozzle?

[KelvinZero]

Hi. Im just a layman so don't take this as authorative:
The particle lens idea is cool but I think it would need a pretty uniform point source to begin with?
My understanding is that the solar wind is swirling around in all sorts of directions rather than just radiating from the sun. I think the movement makes currents and the currents make magnetic fields and the fields bend particles and the result is they all sort of swirl around in complicated ways

Apparently "beamed particle propulsion" is a thing that has papers written on it by fairly well known physicists. Their papers might speculate on how far a beam can travel if you could get it collimated in the first place:

https://en.wikipedia.org/wiki/Beam-powered_propulsion#Direct_impulse

Another beam-pushed concept would be to use a magnetic sail or MMPP sail to divert a beam of charged particles from a particle accelerator or plasma jet.[14] Landis proposed a particle beam pushed sail in 1989,[7] and analyzed in more detail in a 2004 paper.[15] Jordin Kare has proposed a variant to this whereby a "beam" of small laser accelerated light sails would transfer momentum to a magsail vehicle.[16]