At the Cornell University Laboratory of Elementary Particle Physics
(LEPP), Valery Shemelin, Rongli Geng and Hasan Padamsee have reached a
world record accelerating field gradient of 46 MV/m in a single
superconducting accelerator cavity, expanding the possibilities for the
proposed International Linear Collider.
"If we can achieve this gradient in a nine-cell structure with this
technique, it would give us more 'overhead' in our design," said Shekhar
Mishra, Head of ILC Efforts at Fermilab. "Possible options resulting
from this 'overhead' would be that we could make the machine shorter in
length at the same energy or higher energy reach at reduced luminosity,
keeping the same beam power."
The current best gradient for nine-cell accelerating structures is
35-40MV/m achieved by the TESLA Collaboration at DESY. New ideas are
usually proved in single cell cavities before addressing the technical
challenges of multi-cell accelerating units, and an important R&D goal
is to push gradients even higher for TeV energies or cost savings.
But above 40 MV/m, the surface magnetic field approaches the limit where
superconductivity breaks down. Shemelin, Geng and Padamsee altered the
shape of the cavity, lowering the surface magnetic field by 10% and
preserving superconductivity. The new cavity shape has the same beam
aperture as the TESLA cavity, meaning the beam dynamics are likely to be
similar to those of TESLA. cavity.
Similar projects on the way at Jlab-DESY-KEK have achieved a gradient of
about 40 MV/m. But the beam aperture of the new shapes is smaller than
that of the TESLA cavity, and hence the effects on the beam need to be
evaluated. The working group on the High-Gradient Cavities at the KEK
ILC workshop has endorsed the High Gradient R&D efforts.