H. Nakayama

The interaction region of KEKB

Abstract An asymmetric-energy collider of 8 GeV electrons and 3.5 GeV positrons, KEKB, has been operating at KEK since 1998. On July 9, 2001 it achieved the highest record of luminosity, 4.5×10 33 cm −2 s −1 . This paper describes the interaction region (IR) extending about 8 m from the interaction point (IP) along each beam direction. The main machine components in the IR are focusing quadrupole magnets, compensation solenoids, and vacuum chambers, which are positioned on movable stages. They are designed to focus both beams into collisions with a finite angle crossing.

Beam-transport system of KEKB

The transport lines of the KEKB for positrons and electrons convey the beams separately from the injector linac to the KEKB rings. The length is about 500 m for each line. In order to make the maximum use of the existing tunnels and also to avoid interference with the AR, the beam lines took a serpentine course, resulting in a rather large curvature in the arcs. The consequences were a large number of bends in the arcs with high fields and also a large dispersion function and, thus, a large R56 component. The latter issue is crucial for the KEKB rings, since it results in a longer bunch length at injection. We adopted a special optics that reduces the R56 coefficient sufficiently. We have developed novel water-cooled ceramic chambers for kickers, eddy-current type septum magnets for injection, and a beam-abort system for the rings. The present paper describes the design and current status of the beam lines, the injection system, and the beam-abort system.

Study on Field Measurement and Ground Vibration for Superconducting Solenoid of New g-2 Experiment at J-PARC

Basic R&Ds of a superconducting solenoid for a new g-2 experiment at J-PARC are on going. High uniformity of magnetic field below 0.1 ppm is required for the g-2 experiment within a storage region of 33.3±5 cm in radius and ±10 cm in height. Two R&Ds have been started to develop the magnet with such high uniformity; a development of a precise field monitoring system and a study of seismic ground vibration. The prototype monitoring system using continuous wave type NMR probe for horizontal MRI solenoid has been built and tested. Cross-check between NMR and Hall probe has been also carried out. The seismic ground vibration has been measured at Materials and Life science Facility, MLF, in J-PARC. Based on the measured results, the spectrum analysis of the iron yoke has been performed using ANSYS.

Recent Progress at KEKB

We summarize the machine operation of KEKB during past one year focusing on progress for this period.

Field trapping and shielding measurements within a cylindrical hole in a block of Sm-Ba-Cu-O bulk superconductor

Field trapping and shielding experiments were performed using high-T/sub c/ bulk superconductor with a cylindrical hole in it. An array of Hall probes was used to measure the field inside the hole as a function of position and applied field. The trapping of magnetic field in the hole was accomplished by cooling the bulk superconductor in the presence of an applied field and then gradually reducing the applied field to zero. Shielding experiments were carried out by cooling the superconductor in the absence of a magnetic field and then gradually applying an external field. This paper describes the results of these experiments.

Estimation of the longitudinal impedance of the ATF damping ring

In order to estimate the possibility of bunch lengthening in the ATF damping ring, the longitudinal broadband impedance of the ring was evaluated. The inductance was so small, that the bunch lengthening should not be observed in the ATF damping ring. It is found that the total mod Z/sub ////n mod is less than 0.3 infinity . Therefore bunch lengthening should not be a problem in the ATF damping ring.<<ETX>>

Commissioning of the Phase-I SuperKEKB B-Factory and Update on the Overall Status

The SuperKEKB B-Factory at KEK (Japan), after few years of shutdown for the construction and renovation, has finally come to the Phase-1 commissioning of the LER and HER rings, without the final focus system and the Belle II detector. Vacuum scrubbing, optics tuning and beam related background measurements were performed in this phase. Low emittance tuning techniques have also been applied in order to set up the rings for Phase-2 with colliding beams next year. An update of the final focus system construction, as well as the status of the injection system with the new positron damping ring and high current/low emittance electron gun is also presented.

Beam-beam effects observed at KEKB

At KEKB, a dedicated machine experiment on crab crossing has been carried out for about 4.5 months. Some of the beam-beam effects observed with crab crossing, which include a beam lifetime issue, are discussed in comparison with those with a finite crossing angle of plusmn11 mrad.