Abstract:
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Achieving high gradients in superconducting radiofrequency (SCRF) cavities was
stumbling on two main limitations : quench and field emission. We will
describe the significant progress that has been made recently to understand and
overcome these phenomena. Moreover, the understanding of the residual
resistance of niobium has enable us to measure cavities routinely having a
quality factor above 7.1010 at low fields, while still being limited by the
BCS resistance even at temperatures as low as 1.5 K. After demonstrating these
improvements, a new limitation encountered at high fields will be described :
A strong slope in the Q vs Eacc curve, showing up at magnetic field levels over
100 mT.
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