Performance of superconducting storage ring cavities at 1500 MHz

Application of superconducting cavities in high energy storage rings offers the advantage of considerable power savings over normal conducting structures. The fabrication, processing and performance of three five-cell, elliptically shaped 1500 MHz storage ring cavities, which have been built from reactor grade niobium and which are equipped with fundamental mode power couplers and higher order mode couplers, are described. Q-values of 5 × 10⁹at 2.1°K and accelerating gradients of 9 MV/m have been achieved using commercial grade niobium. The use of higher thermal conductivity niobium offers the possibility of thermally stabilizing the material and increasing the tolerable power dissipation. With niobium of three times the thermal conductivity of reactor grade material accelerating gradients up to Eacc= 15.3 MV/m corresponding to peak magnetic surface fields of 71.6 mT have been achieved.