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Physicists Plan to Build a Bigger LHC
ananyo writes "When Europe's Large Hadron Collider (LHC) started up in 2008, particle physicists would not have dreamt of asking for something bigger until they got their US$5-billion machine to work. But with the 2012 discovery of the Higgs boson, the LHC has fulfilled its original promise — and physicists are beginning to get excited about designing a machine that might one day succeed it: the Very Large Hadron Collider. The giant machine would dwarf all of its predecessors (see 'Lord of the rings'). It would collide protons at energies around 100 TeV, compared with the planned 14TeV of the LHC at CERN, Europe's particle-physics lab near Geneva in Switzerland. And it would require a tunnel 80-100 kilometres around, compared with the LHC's 27-km circumference. For the past decade or so, there has been little research money available worldwide to develop the concept. But this summer, at the Snowmass meeting in Minneapolis, Minnesota — where hundreds of particle physicists assembled to dream up machines for their field's long-term future — the VLHC concept stood out as a favorite."
This is true, but no so simple: in a straight line, you gain energy with the distance. When going round, you lose energy to stay in the loop as a function of the radius (the infinite radius case brings you back to the straight line). Thus, each time you want more energy, your collider ring needs to have considerably larger radius (following a third power law). At some point (basically the point after this proposal) you have to loop around the solar system :)
There's a tradeoff in circular/linear accelerators. Linear accelerators let you collide leptons (usually electrons) efficiently and leptons provide a MUCH cleaner signal. A comparable energy circular accelerator can be shorter, but due to bremsstrahlung losses, you have to collide hadrons (like protons), which provides a much messier signal.
After you do some rough calculations of what particles you can collide, their energies and the number of interactions per second, you then take those numbers and plug them into a model of a hypothetical detector along with a number of theories you'd like to explore to see which configuration gives you the biggest "bang for your buck"
The issue is that different people are more interested in probing different kinds of physics and it's impossible to make a detector/accelerator that's sensitive enough to fully probe everything, so big arguments happen at places like Snowmass. We know that we basically can only ask for one multi-billion dollar accelerator, so everyone's fighting to keep their pet research alive.