Design and Test of a Superconducting Quarter-Wave-Resonator

A superconducting quarter-wave-resonator at 325 MHz has been designed that could be used as a debuncher for the Heidelberg postaccelerator. The design study utilized the computer codes SUPERFISH and URMEL as well as a theory considering the quarter-wave-resonator as a piece of transmission line shorted at one end. These calculations were used to optimize H
_p
/ε
_acc
, E
_p
/ε
_acc
and U/ε
²
_acc
. According to measurements with a model resonator the copper body of a first prototype resonator has been machined. In first experiments with an electrochemically plated lead surface an unloaded quality Q
₀
= 6 × 10
⁷
has been measured. The highest accelerating field obtained in that test amounted to ε
_acc
= 1.8 MV/m at Q
₀
= 1.0 × 10
₇
.