KEKB is one of the most challenging accelerators in the world aiming to achieve the peak luminosity of 1×1034 cm-2s-1 for the study of B-meson physics. To achieve such a high luminosity, ampere-class beams of electron and positron have to be accumulated in the 8 GeV-ring (HER) and the 3.5 GeV-ring (LER) separately, and be controlled precisely to collide each other in the BELLE detector located at the collision point. These intense beams need the accelerating RF cavities that have sufficiently damped higher modes (HOM) not to excite uncontrollable beam instabilities caused by the field induced by the beam. Therefore new accelerating cavities have been developed in KEKB for both superconducting (SC) and normal conducting (NC) cavities. Since the beginning of machine commissioning in 1998, the peak luminosity has been improved gradually as increasing the beam intensity of both rings, and achieved the peak luminosity of 1.4×1034 cm-2s-1 with the beams of 1.2 A in HER and 1.6 A in LER so far. In HER, eight SC damped cavities have been installed together with twelve NC cavities, and share the RF voltage of 11 MV and the beam power of 2.4 MW. This superior accelerating performance has opened up a new application of high intensity acceleration for the SC cavity.
The fundamental two-phase flow characteristics of slush nitrogen in a pipe are numerically investigated to develop effective cooling performance for long-distance superconducting cables. First, the governing equations of two-phase slush nitrogen flow based on the unsteady thermal non-equilibrium two-fluid model are constructed and several flow characteristics are numerically calculated taking into account the effects of slush volume fraction, thermodynamic behavior of slush, and duct shape. Furthermore, the numerical results are compared with previous experimental results on pressure loss measurement and visualization measurement in two-phase slush nitrogen flow along the longitudinal direction of the pipe. According to this research, it is found that reducing the pressure loss using a two-phase slush flow is possible under the high Reynolds number condition and by applying the appropriate volume fraction of slush particles. The optimized thermal flow conditions for cryogenic two-phase slush nitrogen with practical use of latent heat for slush melting are predicted for the development of a new type of superconducting cooling system.