10 The Largest Accelerators and Colliders of Their Time
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of one coil returns through the aperture of the neigbouring coil and not through the
iron. Another novel feature of the LHC magnets is the cooling by superfluid helium
which extends the achievable field into the 9 T regime. A significant cost reduction
is achieved by the fact that only one cryostat system is needed for both particle
beams. The compactness of the magnets was very important for the installation in
the tunnel, it would have been extremely demanding if not impossible to mount two
separate proton storage rings in the narrow LEP tunnel.
The elegance and cost-effectiveness of LHC becomes obvious in comparison
with the Superconducting Super Collider SSC project which was promoted in the
USA in the 1980s. Here two counterrotating 20 TeV proton beams were planned
to be accelerated and stored in two separate rings equipped with magnets of an
improved Tevatron design. This “conservative” approach turned out far more costly
than the innovative LHC solution. The SSC was cancelled in 1993 for budget
reasons.
10.5.2 HERA Experience and the Design of Future
Lepton-Hadron Colliders
The scientific results from HERA on quantum chromo-dynamics (QCD) are an
essential pillar of our present understanding of the nature of strong interactions.
These insights are of critical importance for the interpretation of the measurements
of particle production processes at the Large Hadron Collider (LHC) at CERN.
There are, however, very interesting phenomena and physics questions that were
raised by the HERA experiments but remain unanswered as of today:
• How does QCD lead to the rich and complex structure we observe in nuclei?
• How are quarks and gluons and their spins distributed in nucleons and nuclei?
• Why do protons and neutrons have spin 1/2?
• How does the increase of gluon density with decreasing gluon fractional
momentum x saturate?
• What is the distribution of partons that seed the new form of matter discovered
at RHIC, the quark-gluon plasma?
The U.S. Nuclear physics community has formulated a physics program that
addresses these questions in a White Paper [175]. This physics program is based
on an Electron Ion Collider (EIC), which can provide collisions between polarized
electrons and ions ranging from polarized proton to Uranium over a wide range
of center of mass energies 29–140 GeV with a high luminosity in the order of
10 34 cm −2 s −1 . There are two designs for an EIC under development in the U.S.,
one by Thomas Jefferson National Accelerator Facility, called JLEIC [176], and one
by Brookhaven National Laboratory, called eRHIC [177]. Both designs are based on
intersecting storage rings.
635
of one coil returns through the aperture of the neigbouring coil and not through the
iron. Another novel feature of the LHC magnets is the cooling by superfluid helium
which extends the achievable field into the 9 T regime. A significant cost reduction
is achieved by the fact that only one cryostat system is needed for both particle
beams. The compactness of the magnets was very important for the installation in
the tunnel, it would have been extremely demanding if not impossible to mount two
separate proton storage rings in the narrow LEP tunnel.
The elegance and cost-effectiveness of LHC becomes obvious in comparison
with the Superconducting Super Collider SSC project which was promoted in the
USA in the 1980s. Here two counterrotating 20 TeV proton beams were planned
to be accelerated and stored in two separate rings equipped with magnets of an
improved Tevatron design. This “conservative” approach turned out far more costly
than the innovative LHC solution. The SSC was cancelled in 1993 for budget
reasons.
10.5.2 HERA Experience and the Design of Future
Lepton-Hadron Colliders
The scientific results from HERA on quantum chromo-dynamics (QCD) are an
essential pillar of our present understanding of the nature of strong interactions.
These insights are of critical importance for the interpretation of the measurements
of particle production processes at the Large Hadron Collider (LHC) at CERN.
There are, however, very interesting phenomena and physics questions that were
raised by the HERA experiments but remain unanswered as of today:
• How does QCD lead to the rich and complex structure we observe in nuclei?
• How are quarks and gluons and their spins distributed in nucleons and nuclei?
• Why do protons and neutrons have spin 1/2?
• How does the increase of gluon density with decreasing gluon fractional
momentum x saturate?
• What is the distribution of partons that seed the new form of matter discovered
at RHIC, the quark-gluon plasma?
The U.S. Nuclear physics community has formulated a physics program that
addresses these questions in a White Paper [175]. This physics program is based
on an Electron Ion Collider (EIC), which can provide collisions between polarized
electrons and ions ranging from polarized proton to Uranium over a wide range
of center of mass energies 29–140 GeV with a high luminosity in the order of
10 34 cm −2 s −1 . There are two designs for an EIC under development in the U.S.,
one by Thomas Jefferson National Accelerator Facility, called JLEIC [176], and one
by Brookhaven National Laboratory, called eRHIC [177]. Both designs are based on
intersecting storage rings.