KEK, Ibaraki
A few issues on the path of the luminosity upgrade of KEKB B-Factory is described, including coherent synchrotron radiation, design of the interaction region, crab crossing, and high current operation. These issues will raise more obstacles on the upgrade with the High-Current Scheme. As an alternative, {¥it Nano-Beam Scheme} should be considered as a possible option for the upgrade.
KEK, Ibaraki
SLAC, Menlo Park, California
It is well known that the beam-beam interaction has a focusing effect and therefore causes a dynamical beating of beta function around the rings. This effect becomes greatly enhanced when a collider, such as KEKB, is operated near half integer. The beating makes it difficult to interpret the measurement of horizontal beam size. We derived two coupled nonlinear equations and solved them analytically to obtain the beam sizes at the interaction points, taking into account of dynamical beta and emittance. It has been demonstrated its effectiveness using actual measured data at the synchrotron light monitors. It is expected that it will be implemented in the control room.
KEK, Ibaraki
KEK is studying the design of the superconducting final focus quadrupoles for the Super KEKB. The system consists of quadrupole-doublet cooled at 1.9 K. The vertical focusing quadrupole has the maximum magnetic field more than 8 T in the superconducting coils. The field gradient at the magnet center is more than 80 T/m and the effective magnetic length is 0.25 m. The horizontal focusing quadrupole is designed with the field gradient of 9.5 T/m and the effective magnetic length of 1.0 m. These magnet parameters will be iterated in the process of optimizing the beam optics. In this paper, the conceptual design of final focusing system and magnets will be reported.
KEK, Ibaraki
Lattice design for SuperKEKB is based on the present KEKB lattice. The unit-cell structure of KEKB has a wide range of flexibility, therefore main beam-optical parameters can be adjusted without changing the arcs. The interaction region (IR) and the other straight sections are changed to squeeze the vertical beta function to 3 mm at IP, keeping sufficient dynamic apertures. Recent progress such as a new design of IR with superconducting quadrupole magnets at 1.9 K, traveling focus scheme by using crab cavities, local chromaticity correction for the high energy ring, is presented.
KEK, Ibaraki
Beam-beam tune shift parameter characterizes the strength of the nonlinear interaction due to the beam-beam collision. The tune shift has been measured in many e+e- colliders and has been an indicator for the collider performance. The record for the tune shift is known as 0.07-0.1 depending on the parameter of the collider, especially the radiation damping rate. We discuss the fundamental limit of the tune shift can be very high (>0.2) depending on the choice of collider parameter, which concerns operating point near the half integer tune, head-on collision and travel focus.
KEK, Ibaraki
Two synchrotron light sources of the Photon Factory storage ring (PF-ring) and the Photon Factory advanced ring (PF-AR) have been stably operated at KEK. PF-ring covers the photon-energy range from VUV to hard X-ray using a 2.5 GeV (sometimes 3.0 GeV) electron beam. PF-AR is mostly operated in a single-bunch mode of 6.5GeV to provide pulsed hard X-rays. Recently, the operation has progressed to realize a so-called top-up injection at PF-ring. In a single-bunch mode, the continuous injection to preserve a constant beam current of 51 mA has been carried out since February 2007. In addition, the injection with continuing the experiments has been successfully operated in a multi-bunch mode since October 2008. At PF-AR, sputter ion pumps have been extensively reinforced to prolong the beam lifetime and to reduce the frequency of sudden lifetime drops by substituting for distributed ion pumps, which are considered as one of the dust sources. In this conference, we present the recent progress of the operation at PF-ring and PF-AR including machine developments.
KEK, Ibaraki
Crab cavities were installed at KEKB at the beginning of 2007. The beam operation with the crab cavities is in progress. In this paper, machine performance with crab crossing is described focusing on a specific luminosity and a beam lifetime issue related to the dynamic beam-beam effects.
SLAC, Menlo Park, California
KEK, Ibaraki
Using a streak camera, we measured the longitudinal profiles of a positron bunch in the Low Energy Ring (LER) of KEKB at various currents. The measured charge densities were used to construct a simple Q=1 broadband impedance model. The model with three parameters not only gave an excellent description of longitudinal dynamics for a positive momentum compaction factor but also for the negative ones, including bunch shortening bellow a threshold and bursting modes beyond the threshold. Furthermore, our study indicated that the threshold of microwave instability was about 0.5 mA in bunch current in the LER. At the nominal operating current 1.0 mA, there was a 20% increase of the energy spread. The results of measurement, analysis, and simulations will be presented in this paper.