T. Mimashi

KEKB beam instrumentation systems

For the stable high-luminosity operation and luminosity increase, the electron and positron storage rings of the KEK B-Factory (KEKB) is equipped with various beam instrumentations, which have been working well since the start of the commissioning in December, 1998. Details and performance of the beam-position monitor system based on the spectrum analysis using DSPs, the turn-by-turn BPM with four-dimensional function available for measurements of the individual bunch position, phase and intensity, the parametric beam-DCCTs designed so as to avoid the magnetic-core-selection problems for the parametric flux modulation, the bunch-by-bunch feedback system indispensable to suppress the strong multibunch instabilities in KEKB, the various optical beam diagnostic systems, such as synchrotron radiation interferometers for precise beam-size measurement, the tune meters, the bunch length monitors and the beam-loss monitors are described. Delicate machine tuning of KEKB is strongly supported by these instrumentations.

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.

The rejuvenation status of TRISTAN accelerator control system

Abstract Ten years have passed since the current control system started the operation of the TRISTAN accelerator. The system uses CAMAC as a front-end electronics, and they are controlled by 25 Hitachi process computers linked by a N to N token ring network. In order to have the ability to perform complicated accelerator operations, there is a strong request to renew these 25 process computers. Firstly, we review how we will rejuvenate the current control system under some constraints, such as the lack of man-power, limited time and financing. This is followed by proposals for the next step of rejuvenation.

Recent Progress at KEKB

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

Gun trigger system for the ATF

Abstract The KEK Accelerator Test Facility (ATF) is under construction. The injector linac is composed of a 240 keV thermionic electron gun, two 357 MHz subharmonic bunchers, prebunchers and a travelling wave buncher followed by high-gradient accelerating structures. The 1.54 GeV damping ring requires the injector linac to provide high intensity multi-bunch beam with a 2.8 ns bunch spacing at a repetition rate of 25 Hz. To reduce the energy spread which comes from multi-bunch or single-bunch beam loading, precise beam timing is necessary. Therefore the trigger system must provide precise signals for single-bunch, double-bunch, 20-bunch and no-beam operation. Temperature compensated fiber optic cables are used for the transmission of the synchronized trigger signals to the high voltage gun station. The performance of this transmission line is described. Many timing signals are also transmitted from the main control room, in which the master RF frequency generator is situated, via this 1.3 μm single mode fiber optic link. The experimental results of the trigger system for the ATF are also given in this paper.

The position monitor using stretched wire technique

The position monitor using the stretched wire method is being developed as a component of the active alignment system for particle accelerator equipment, such as RF cavities and magnets. The RF voltage is supplied to the stretched wire and the monitor measures the change of capacitance between wire and pickup strip. Present resolution, limited by the electronics noise, is about 5 nm.<<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.

THE BEAM TEST FOR THE TI EXTRACTION WINDOW DAMAGE

Ti extraction window will be used at the SuperKEKB beam abort system [1]. The damage of the window caused by the beam was estimated with KEKB electron beam. Thin Ti and Ti alloy plates were tested as candidates of extraction window material. The damages were observed as a function of beam current density. From the result of this experiment, the horizontal spot size on the extraction window was determined for SuperKEKB abort system.

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.

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.