| | The performance of niobium superconducting cavities
for accelerator applications has improved considerably
over the last decade. Individual cavities reach accelerating
gradients close to the theoretical limit (about 50 MV/m),
however sometimes at the expense of a re-treatment
(baking, electro-polishing, rinsing) needed to eliminate an
undesired decrease of the Q-value with the field gradient
(Q-slope, Q-drop). Cures have been developed, but a
generally accepted physical explanation is still missing.
Furthermore, for successful research work on materials
other than niobium, it is of utmost importance to
understand better the limitations in gradient and Q-value
of superconducting cavities. The paper presents an
alternative explanation for the Q-slope and confronts it
with experimental results for 352 and 1500 MHz cavities. | |