LHC portal

http://www.bbc.co.uk/news/science-environment-26250716

Wearing my CERN director imaginary hat, here's how I'd attack son of LHC:

1. Decide what it is: electrons, protons + heavy ions, or both.
Might be able to do 2 beampipes in one tunnel, or could time multiplex (electrons on Tuesdays)

2. Decide what energy to shoot for: LHC will end at 14 TeV, so shoot for an order up, say 150 TeV, to make the step substantial enough to justify implementation, but not too large that we have to wait decades for the tech to catch up.

3. Decide on the magnet strength: aim for twice as strong as the LHC's magnets. Apparently achievable on paper already.

4. Decide on the entire accelerator size: the minimum radius is fixed by the magnets' strength, the energy, and the particle type(s), which we've already determined. Depth is complicated and depends on geography.

Done. Go do it

It is a little more complex than that ... but not much.

We study both lepton and hadron versions.

The lepton version is dominated by synchrotron radiation considerations and therefore RF accelerating voltage. The hadron version is dominated by our ability to bend the beams and therefore magnetic field strength.

Since the hadron version is the priority, this sets the scale. With present technology, suitably pushed, 16 Tesla magnets seem possible. This means a 100km Tunnel (of which around 80km would be arcs) for a 100TeV cm machine.

If new technologies concerning HTS magnet inserts can be perfected this could bring the possibility of 20 Tesla magnets. In this case the tunnel could be made smaller, or the cm energy increased.

by the way, a lepton collider at 350GeV cm in the 100km tunnel would need around 11GV of RF.

It is an optimization process ...