Orbital Ring Particle Accelerator

[Ultimate Steve]

I have almost no knowledge in this field, but...

So say you have two orbital rings around a planet (Say Earth for example), one in LEO and one in GEO. However, due to a miracle in material engineering, both rings are supported by massive towers, making the LEO ring have a decent amount of gravity (GEO one is still weightless).

Now say you want to build a massive particle accelerator in one of the rings. Would the difference in gravity help/hurt how difficult the engineering would be in any way?

 

And related, how much antimatter could you make with a particle accelerator the size of the GEO orbit? Or is there a more efficient way to make antimatter large scale?

[Scotius]

I'd say access to a high quality vacuum would be a bigger boon to builders Of course microgravity would help - they would need to place a whole lot of electromagnets along the way, equip them with very precise positioning control system and voila! You have a very, very large free floating particle accelerator.

It's not a new idea BTW - i've read about it in an old sci-fi book.

[Rakaydos]

There's even a version of the idea that runs the particle accelerator continuously, such that the centrifugal force of the accelerated mass, reacting to magnets forcing them to stay in the accelerator, actually help hold up the ring.

[Hannu2]

6 hours ago, Ultimate Steve said:

I have almost no knowledge in this field, but...

So say you have two orbital rings around a planet (Say Earth for example), one in LEO and one in GEO. However, due to a miracle in material engineering, both rings are supported by massive towers, making the LEO ring have a decent amount of gravity (GEO one is still weightless).

Now say you want to build a massive particle accelerator in one of the rings. Would the difference in gravity help/hurt how difficult the engineering would be in any way?

Engineering would be technomagic from current point of view. Solid structures of orbit size are not possible under current natural laws. Separate bending magnet and acceleration satellites would be better option, but such a project would need much more resources than is possible in foreseeable future.

 

 

6 hours ago, Ultimate Steve said:

And related, how much antimatter could you make with a particle accelerator the size of the GEO orbit? Or is there a more efficient way to make antimatter large scale?

Huge accelerators intend to get as much energy per particle as possible. Losses depend on curvature and therefore the larger radius the higher energies are possible. That would give access to new physics at higher energies. On the other hand, antimatter production does not need extreme energies per particle. Producing as much optimally energetic particles as possible is better and I think huge size would not give significant benefits in antimatter production compared to many smaller and simpler facilities.

[Gargamel]

If you dig through the Royal Insitute lectures on Youtube, there's a pretty good talk about similar stuff, but mainly as an accelerator around the surface of the moon, but he does touch into orbital accelerators.    But, IIRC, an accelerator the size of the moon would suffice enough for 'the next step' in power.     Anything bigger wouldn't be able to reach sufficient energies until is was a ring about the size of the orbit Neptune. 

[Ultimate Steve]

Just now, Gargamel said:

If you dig through the Royal Insitute lectures on Youtube, there's a pretty good talk about similar stuff, but mainly as an accelerator around the surface of the moon, but he does touch into orbital accelerators.    But, IIRC, an accelerator the size of the moon would suffice enough for 'the next step' in power.     Anything bigger wouldn't be able to reach sufficient energies until is was a ring about the size of the orbit Neptune. 

Okay, thank you, that actually works out fairly well as I was considering an accelerator in Kerbin GEO, radius ~3500km and the Moon is ~1700km so that's same order of magnitude.

[Zeiss Ikon]

On 9/3/2018 at 11:15 PM, Scotius said:

It's not a new idea BTW - i've read about it in an old sci-fi book.

There was a book by Larry Niven titled Building Harlequin's Moon that had an antimatter factory ring that reached all the way around the titular moon (which also had a geologically short-lived atmosphere and hydrosphere).  The moon and the antimatter factory were built to make more fuel for a starship that had to make an unscheduled stop.

[KSK]

On 9/4/2018 at 10:07 AM, Hannu2 said:

On the other hand, antimatter production does not need extreme energies per particle. Producing as much optimally energetic particles as possible is better and I think huge size would not give significant benefits in antimatter production compared to many smaller and simpler facilities.

This. With apologies for the horrible font, here is an overview of the Fermilab antiproton source. Its a spallation source - crudely speaking, you accelerate protons to a given energy, smack them into a suitable target and collect the antiprotons that are ejected. According to that summary, the proton energy used is  120GeV which is actually a fairly trivial amount. Back when the Tevatron was running at Fermilab, it was accelerating proton beams to just under 1TeV, so approximately an order of magnitude more energy than was used to generate the antiprotons. The LHC at CERN runs beams at multiple TeV.

As @Hannu said, you want high energy for (hopefully) interesting physics. Antimatter production per se doesn't need particularly high energies - relatively speaking. It's more of a scaling problem - the amount of antiprotons produced at Fermilab was tiny - I think we're talking nanograms, if that.

 

[Ultimate Steve]

6 hours ago, KSK said:

As @Hannu said, you want high energy for (hopefully) interesting physics. Antimatter production per se doesn't need particularly high energies - relatively speaking. It's more of a scaling problem - the amount of antiprotons produced at Fermilab was tiny - I think we're talking nanograms, if that.

Okay. Large accelerators = large energies. But, instead of increasing the energy per particle in the accelerator, could you instead scale up the amount of matter, especially if the accelerator is that big?

[Bill Phil]

53 minutes ago, Ultimate Steve said:

Okay. Large accelerators = large energies. But, instead of increasing the energy per particle in the accelerator, could you instead scale up the amount of matter, especially if the accelerator is that big?

It might be more practical to build a whole bunch of smaller accelerators, if making antimatter was the goal.

If it's too energetic capturing the antiparticles becomes impractical.

[KSK]

7 hours ago, Ultimate Steve said:

Okay. Large accelerators = large energies. But, instead of increasing the energy per particle in the accelerator, could you instead scale up the amount of matter, especially if the accelerator is that big?

I'm definitely moving out of my comfort zone here but I would say 'probably but it's complicated'. I base that purely on some knowledge of the kind of things that CERN are needing to consider when upgrading the LHC to so-called High Luminosity LHC. High luminosity in this context is basically what you're asking for - packing more matter into the particle beams. In CERN's case this is a Good Thing because it gives them a better collision efficiency, so a better chance of observing the kind of rare collision events they're looking for.

You can increase luminosity by physically injecting more particles into your beams or by narrowing the beams down so the same amount of particles occupy a smaller volume. Either way, since we're dealing with charged particles, electrostatic repulsion is not your friend, which means that your magnets need to be stronger to compensate. That's actually one part where an orbital accelerator would make things easier - the massive increase in beam radius means that your magnets can be correspondingly weaker, so you've got vastly more leeway for tweaking the design.

Then you start getting into interesting effects like secondary electron emission and electron multipacting. Again, probably less of a problem if you're not using a beam pipe (which you probably aren't in space - any solid continuous structure encircling a planet wouldn't be stable if I remember correctly  ). But in a beam pipe, SEE and multipacting is a serious thing. Any air molecules in your pipe are going to be very quickly ionised by your circulating particles. Those ions collide with the beam pipe and kick out electrons and then those electrons collide with the pipe and kick out more electrons. Pretty soon you've got  an electron cloud building up, which plays merry hell with beam stability. This is a Bad Thing. If I remember correctly, the beam dumps at the LHC are a fairly hefty chunk of cryogenically cooled copper surrounded by concrete. Dumping one of the circulating beams will chew through an impressive amount of said copper...

For a really big accelerator operating at comparatively low energies, I would expect you can scale up the amount of matter involved but there will be limits. I think @Bill Phil's notion of multiple smaller accelerators is probably a better plan. Apparently you can build fairly compact wakefield accelerators - they might be a good bet.

But one basic problem isn't going to go away. Running any kind of accelerator takes a lot of energy - way more than you get back from annihilating the antimatter produced. I'm guessing that's understood and acceptable for the sake of producing a such a ridiculously energy dense fuel though.

 

Edited September 6, 2018 by KSK

[Ultimate Steve]

23 minutes ago, KSK said:

Running any kind of accelerator takes a lot of energy

Understood. In this scenario the power would be solar, but solar using giant mirrors and lenses capturing ~0.5% of the star's total energy output, so we should be fine in the solar area. And the antimatter would be used to fuel spaceships.

Thank you very much for your help!

[Gargamel]

On 9/6/2018 at 9:30 AM, Ultimate Steve said:

Okay. Large accelerators = large energies. But, instead of increasing the energy per particle in the accelerator, could you instead scale up the amount of matter, especially if the accelerator is that big?

Take a look at this, IIRC he does delve into some of your questions (video I mentioned before):

 

[KSK]

On 9/6/2018 at 10:21 PM, Ultimate Steve said:

Understood. In this scenario the power would be solar, but solar using giant mirrors and lenses capturing ~0.5% of the star's total energy output, so we should be fine in the solar area. And the antimatter would be used to fuel spaceships.

Thank you very much for your help!

Sorry about the late reply, I missed the updates to this thread. But anyway - you're very welcome! 

[Hannu2]

On 9/6/2018 at 11:48 PM, KSK said:

 If I remember correctly, the beam dumps at the LHC are a fairly hefty chunk of cryogenically cooled copper surrounded by concrete. Dumping one of the circulating beams will chew through an impressive amount of said copper...

https://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/components/beam-dump.htm

This source says that energy of beam (total of all circulating protons) is 350 MJ. It is huge amount of energy released in less than 100 microseconds. It is as much of energy as 90 kg TNT (or dynamite) releases in explosion. I can believe that it evaporates significant amount of anything it hits and if target is not actual beam dump intended to handle it there will be very expensive repairs.

 

[KSK]

4 hours ago, Hannu2 said:

https://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/components/beam-dump.htm

This source says that energy of beam (total of all circulating protons) is 350 MJ. It is huge amount of energy released in less than 100 microseconds. It is as much of energy as 90 kg TNT (or dynamite) releases in explosion. I can believe that it evaporates significant amount of anything it hits and if target is not actual beam dump intended to handle it there will be very expensive repairs.

 

I gladly stand corrected. That’s even more impressive than I thought!