S. Yoshimoto

RF systems for the KEK B-Factory

This paper describes the design features and operational status of the RF systems for the KEK B-Factory (KEKB). Two types of new RF cavities have been developed to store very high-intensity beams with many short bunches. The design and performance of the cavities and other critical components, such as the input couplers and HOM dampers, are reported. The configuration of the RF systems is given and descriptions of various control loops are made, including a direct RF feedback loop and a 0-mode damping loop. The effects of transient beam loading due to a bunch gap on bunch phase modulations were simulated and measured. The development of a superconducting crab cavity, which is a component of luminosity upgrade strategy, is also presented.

Commissioning of the KEKB B-Factory

The commissioning of the KEKB B-Factory storage rings started on Dec. 1, 1998. The two rings both achieved a stored current of over 0.5 A after operating for four months. The two beams were successfully collided several times. The commissioning stopped on Apr. 19, taking a 5-week break to install the Belle detector.

Recent Progress at KEKB

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

PF-ring and PF-AR operational status

The present operational status of the Photon Factory storage ring (PF-ring) and the Photon Factory advanced ring (PF-AR) in KEK is reported. The scheduled user times of them were more than 4000 hours in FY2006. In the last summer shutdown, new undulators were installed in both of the rings and have been stably operated. A top-up operation in a single-bunch mode was demonstrated for six days in February 2007 druring the shutdown of KEKB at the PF-ring.

Experiment of the RF feedback using a parallel comb filter

In high beam-current storage rings like KEK B-factory, severe coupled-bunch longitudinal instability can be driven by the accelerating mode of significantly detuned RF cavities. The RF feedback with a comb filter, which can reduce the effective cavity impedance at the synchrotron sidebands of the revolution harmonics, is a possible way to damp the instability. This paper describes the results of the experimental RF feedback loop, which includes a N-path filter referred to as a parallel comb filter, a choke mode cavity, and a 1.2 MW klystron. With the feedback, the real part of the cavity impedance was reduced by 16 dB to 24 dB, at the five synchrotron sidebands 100 kHz apart each other.

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.

Status of the 6.5‐GeV Photon Factory Advanced Ring

The Photon Factory Advanced Ring (PF‐AR) is a 6.5‐GeV synchrotron light source at the High Energy Accelerator Research Organization (KEK). It can provide high‐flux hard X‐rays for such research as the materials science, structural biology and medical applications. The PF‐AR has five insertion devices including four in‐vacuum undulators. It is operated with a single bunch which fits for time‐resolved experiments. A special 5‐GeV operation is partly provided for a clinical application. An initial beam current and a beam lifetime are 60 mA and approximately 14 hours, respectively. Recent developments include an installation of a new in‐vacuum undulator (U♯NW14‐36) to the west rf section, which was accompanied by transferring two rf cavities to other section. The undulator has been successfully operated at a minimum magnetic gap of 10 mm. We also carried out such accelerator studies as a successful test of beam injection using a pulsed quadrupole magnet, a study of low emittance optics, an establishment of tw...

Status of PF-AR

The PF‐AR is a full‐time single‐bunch light source for SR experiments in the X‐ray region. Electrons are injected at 3.0 GeV and ramped up to the final energy of 6.5 GeV for normal user operation or 5.0 GeV for medical application. The typical initial beam current is 55 mA at 6.5 GeV and the beam lifetime is 15 h at 50 mA. The initial single‐bunch impurity better than 10−8 was achieved, however, degradation of the impurity during the users’ run has to be solved. Since the present emittance of 290nm⋅rad is not satisfactory, we are making an effort to realize the minimum attainable emittance of 160nm⋅rad. The high quality of pulse X‐ray has brought us abundant occasions to do time‐domain and/or time‐resolved measurements.

Lattice diagnostics using single kick closed orbit at KEKB

We have measured beta functions using single kick closed orbit at KEKB. The measured beta functions were compared with the model lattice and gradient errors were extracted from the result in a beta beat. The gradient errors were also obtained by changing strength of steering magnets and measuring beam positions as the second method. The methods of the error estimation and preliminary results are reported.