On the Feasibility of a Tripler Upgrade for LHC

Recent developments in the performance of superconductors and the design of high-field superconducting dipoles have opened the possibility to extend dipole field strength to ~25 Tesla in the arc dipoles of a future hadron collider. Design issues are presented for a concept of a Tripler upgrade of LHC, in which a second dual ring would be installed over the LHC ring in the same tunnel. Proton beams from LHC would be transferred to the Tripler midway through the LHC cycle and accelerated to ~20 TeV/beam for collisions. A number of obvious issues are explored. Synchrotron radiation power would be 80 times greater, but the critical energy would come as soft X-rays rather than hard UV, and so could be absorbed locally on ~150 K photon stops following each dipole so that total refrigeration power could perhaps be no more than that for LHC. Synchrotron damping would be dramatically enhanced in the Tripler compared to LHC, with damping times of ~one hour. Alternatives for beam transfer and low-beta insertions will be discussed. Like LHC, the Tripler would access new mass scales primarily through gluon fusion. The Tripler should reach about twice the mass scale attainable with LHC.