"Particle physicists are pondering the successor for the Large Hadron Collider (LHC), the 27 km (circumference) tunnel on the Franco-Swiss border which has produced experimental data to confirm the existence of the Higgs boson. CERN recently announced it was studying several proposals for a next generation hadron collider; perhaps the most intriguing was TLEP, an enormous (80-100 km) circular collider to be built adjacent to the LHC, that would pass below Lake Geneva. A group of physicists mostly associated with Texas A&M University have counterproposed reviving the Superconducting Supercollider (SSC), a partly-built 87 km circular collider south of Dallas that was abandoned in 1993 after Congress cancelled the project.
The Texas A&M physicists argue that a completed SSC would be powerful enough to generate the Higgs boson in quantities that would allow detailed study (a 'Higgs Factory' in the authors' words), while saving money relative to competing proposals since 45 percent of the tunnel has already been drilled. But then it gets real interesting; the authors propose an additional tunnel, an enormous 270 km circumference collider that would encircle the city of Dallas. Protons would be accelerated in the SSC tunnel for injection into the hadron collider."
Recently people in HEP have been talking about a 100 TeV collider [blogspot.com] more seriously than they have in the past. The problem is, with the repeated failure of beyond-the-Standard-Model theoretical predictions (Supersymmetry, etc), it seems foolhardy to construct another x billion dollar/euro project that has the potential of finding nothing new.
This proposal is interesting though, because they propose a relatively modest machine for the SSC tunnel, with weaker magnets than the LHC. They also propose reuse of technology from the CEBAF 12 GeV upgrade for the injection linac. So presumably there would be minimal R&D required to build this machine.
The bigger ring, though, is total pie-in-the-sky. The magnet tech is still under development, and no matter how you slice it, it's gonna cost way too much. Still, I guess it could happen, and then the question becomes "where do you build it?" The obvious choices are CERN and Fermilab, but at this point it never hurts to throw your hat in the ring.