Questionable Questing

But the required throughput of the laser is orders of magnitude less than the particle accelerator, so it would still be useful. And even hard XFELs with decent mirror sizes push the weapon into "easily multiple light minutes" territory.

Doesn't required laser power also rise with particle speed because there's less time to focus the beam before the laser diverges too much to be useful to the focusing, so for a faster particle beam you have to increase the strength of the laser to focus it faster?

I don't think any lasers in aliceverse use focusing mirrors because there's too much light weapons fire flying around for anything that fragile.

I don't see why you'd use a graser enhanced particle beam though since once you could build the effective graser you'd just use it as the weapon instead of the particle beam. The graser seems harder to defend against.

Aliceverse uses momentum exchange focusers; they're somewhat like cheaty mirrors.

So the photons, after coupling with the particles, not only induce a gradient in the particle beam, but are in turn focused by the particles in the beam, which lets the NASA's proposed 60GW beam hit a sub 100 meter sail at 500AU (theoretically).

Even a partial optical tweezer effect (without the particle stream focusing the laser) would still massively decrease divergence, though there is the potential for particle beam instability if the photons are not coupled to the particles.

Are you putting together your post about particle beams in the aliceverse?

What do you see as their weaknesses? How would you defend against them? How small could you make one that would be effective?

In progress.

I think there is an issue with the laser/particle-beam coupling idea when weaponised; because the laser moves faster than the particle beam, the two will separate and lose cohesion after some amount of time and distance. For PROCSIMA's use case this is less relevant due to the beam being fired at the same spot for a long period, but for a weapon which may need to change targets this can be an issue.

Simply continuing the laser after the particle beam has changed targets wouldn't work, because without the particle beam it'll spread out before it can catch up.

Basically, it would be important to push the particle beam into the ultrarelativistic region in order to make an effective long-range weapon.

The laser doesn't need to be continuous, most of the focusing effect is in the first thousand kilometers. After that the particle beam can continue without the laser.

This does mean the laser arrives well before the beam.

I do not believe you, IH - I'm not accusing you of lying, but if you're calling it "focussing" I don't think you understand what beam divergence actually is.

The laser isn't a significant damage source in a laser coupled particle beam. The laser is just used to decrease the divergence of the particle beam. It has most of that effect in the first thousand kilometers. This lets you get a tight enough particle beam to go millions of kilometers while keeping tight enough for use as a weapon.

At that range the laser will be spread out into uselessness, and will arrive significantly before the particle beam, but the particle beam will still be tight and effective.

As I said, you don't seem to understand what's going on here - certainly, not well enough to be telling me what I'm doing wrong.

Focussing creates *systematic* convergence of a beam. It is useful for converting a parallel beam into a focussed beam that comes to a near-point. It is *not* useful for counteracting *random* spreading, such as that of a particle beam (or that which prevents a non-laser light source from being focussed down to a point).

The reason optical tweezing works is not because it cools the beam, but because it is generating a force pulling all the particles together.

They won't *stay* together once the laser's no longer there, because they still have those random individual motions. That's like saying that if you put air in a box (with the outside of the box in vacuum), the air will stay there once the box is removed.

If you've cooled the air in the box to near absolute zero the air *will* stay there though. The random motion is dependent on temperature, at extremely low temperatures the random motion is extremely low.

I did it, and I am very tired now. Hopefully ShaperV appreciates it.

You can cool the transverse motion of the beams dramatically (using a low velocity/multipass loop) before feeding into accelerator, you can use a very high quality ion source, and heavy beams diverge less proportionally.

IH: To extend the metaphor a little further, if the air was at absolute zero, you wouldn't have needed a box in the first place.