KEK, Ibaraki
KEK is studying the design of the interaction region quadrupoles for the SuperKEKB of which the two beams of 4GeV/7GeV for LER/HER have a crossing angle of 83 mrad. For each beam, the final beam focusing system consisting of superconducting and permanent magnets is studied. The superconducting quadrupoles close to the interaction point for each beam are located in the compensation superconducting solenoid which cancels the solenoid field by the particle detector, Belle. These magnet parameters are optimized to obtain higher luminosity. In this paper, the design progress of final focusing system and magnets will be reported.
KEK, Ibaraki
Optics parameters at the interaction point, beta, x-y coupling, dispersion and their chromatic aberrations, seriously affect the beam-beam performance as is shown in experiments and simulations. The control of the optics parameters is essential to maintain the high luminosity in KEKB. They drift day by day, or before and after the beam abort. They were often monitored at intervals of the operation with taking the study time. They are recently measured during the physics run using a pilot bunch without collision. We show the measured the optics parameters and their variations and discuss the relation to the luminosity.
KEK, Ibaraki
Using a weak-strong beam-beam code, in which the symplectic maps for the linear coupling and chromatic aberrations were implemented, the luminosity degradation caused by the linear and chromatic X-Y couplings at the interaction point (IP) were evaluated for the SuperKEKB project under design. The linear and chromatic X-Y couplings were estimated through modeling the machine errors using random seeds, based on a baseline design of the SuperKEKB rings. It was found that the linear and chromatic X-Y couplings can potentially degrade the luminosity performance.
KEK, Ibaraki
University of Tokyo, Tokyo
Tohoku University, Graduate School of Science, Sendai
SuperKEKB is the upgrade plan of the current B-factory experiment with the KEKB accelerator at KEK. Its luminosity is designed to be 8x1035 /cm2/s (40 times higher than KEKB) and the integrated luminosity is expected to be 50 ab-1. In SuperKEKB, it is important to evaluate the beam induced BG and design the interaction region (IR) to assure the stable detector operation. To estimate the beam induced BG, we construct the beam-line simulation based on the GEANT4 simulation. In this paper, we report the BG evaluation and the IR design for SuperKEKB.
KEK, Ibaraki
Electron cloud instabilities are a great concern for the KEKB, an electron/positron collider. In order to study wakefield effects of electron cloud, a test bunch was injected behind a bunch train with the solenoid fields off, where cloud density rapidly decayed. A current-dependent tune shift and the tune spread of a test bunch were measured as a function of the bunch current while varying the bucket position of a test bunch. The vertical tune shift indicated a strong defocusing force together with widened tune spread in a region of relatively low cloud density and low bunch current. However, the vertical tune shift changed to a focusing force at high cloud density and high bunch current. On the other hand, the horizontal and vertical tune spreads tended to approach a constant value as increasing the bunch current. The turning current is approximately equal to the threshold current of the vertical size blow-up.
KEK, Ibaraki
KEKB is an e-/e+ collider for the study of B physics and is also used for machine studies for future machines. The peak luminosity of KEKB, which is the world-highest value, has been still increasing. This report summarizes recent progress at KEKB.
