Proton Colliders at the Energy Frontier

Since the first proton collisions at the CERN Intersecting Storage
Rings (ISR)  hadron colliders have defined the energy frontier.
Noteworthy are the conversion of the Super Proton Synchrotron (SPS)
into a proton-antiproton collider, the Tevatron proton-antiproton
collider, as well as the abandoned SSC in the United States, and
early forward-looking studies of even higher-energy colliders.

Hadron colliders are likely to determine the pace of particle-physics
progress also during the next hundred years. Discoveries at past hadron
colliders were essential for establishing the so-called Standard Model of
particle physics. The world’s present flagship collider, the Large Hadron
Collider (LHC), including its high-luminosity upgrade (HL-LHC),
is set to operate through the second half of the 2030’s. Further increases
of the energy reach during the 21st century require another, still more
powerful hadron collider. Three options for a next hadron collider are
presently under investigation. The Future Circular Collider (FCC) study,
hosted by CERN, is designing a 100 TeV collider, to be installed inside a
new 100 km tunnel in the Lake Geneva basin. A similar 100-km collider,
called Super proton-proton Collider (SppC), is being pursued by CAS-
IHEP in China. In either machine, for the first time in hadron storage
rings, synchrotron radiation damping will be significant, with a damping
time of the order of 1 hour. In parallel, the synchrotron-radiation power
emitted inside the cold magnets becomes an important design constraint.
One important difference between FCC and SppC is the magnet technol-
ogy. FCC uses 16 Tesla magnets based on Nb3Sn superconductor, while
SppC magnets shall be realized with cables made from iron-based high-
temperature superconductor. Initially the SppC magnets are assumed to
provide a more moderate dipole field of 12 T, but they can later be pushed
to a final ultimate field of 24 T. A third collider presently under study is
the High-Energy LHC (HE-LHC), which is a higher energy collider in the
existing LHC tunnel, exploiting the FCC magnet technology in order to
essentially double the LHC energy at significantly higher luminosity.