Y. Ohnishi

The KEKB injector linac

Abstract An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

KEKB accelerator control system

The KEKB accelerator control system including a control computer system, a timing distribution system, and a safety control system are described. KEKB accelerators were installed in the same tunnel where the TRISTAN accelerator was. There were some constraints due to the reused equipment. The control system is based on Experimental Physics and Industrial Control System (EPICS). In order to reduce the cost and labor for constructing the KEKB control system, as many CAMAC modules as possible are used again. The guiding principles of the KEKB control computer system are as follows: use EPICS as the controls environment, provide a two-language system for developing application programs, use VMEbus as frontend computers as a consequence of EPICS, use standard buses, such as CAMAC, GPIB, VXIbus, ARCNET, RS-232 as field buses and use ergonomic equipment for operators and scientists. On the software side, interpretive Python and SAD languages are used for coding application programs. The purpose of the radiation safety system is to protect personnel from radiation hazards. It consists of an access control system and a beam interlock system. The access control system protects people from strong radiation inside the accelerator tunnel due to an intense beam, by controlling access to the beamline area. On the other hand, the beam interlock system prevents people from radiation exposure by interlocking the beam operation. For the convenience of accelerator operation and access control, the region covered by the safety system is divided into three major access control areas: the KEKB area, the PF-AR area, and the beam-transport (BT) area. The KEKB control system required a new timing system to match a low longitudinal acceptance due to a low-alpha machine. This timing system is based on a frequency divider/multiply technique and a digital delay technique. The RF frequency of the KEKB rings and that of the injector Linac are locked with a common divisor frequency. The common divisor frequency determines the injection timing. The RF bucket selection system is also described. r 2002 Elsevier Science B.V. All rights reserved.

A high-resolution cylindrical drift chamber for the KEK B-factory

The Central Drift Chamber of the BELLE detector at the KEK B-factory is a cylindrical wire chamber device that uses a helium-based gas and aluminum field wires and is situated in a 1.5 T magnetic field. The transverse momentum resolution for charged tracks with 1.0 GeV/c transverse momentum is 0.35%. This paper describes the chambers configuration and performance.

Test of charge-to-time conversion and multi-hit TDC technique for the BELLE CDC readout

We tested a new CDC readout scheme utilizing a Charge-to-Time conversion (QTC) technique and multi-hit TDC to record both time and charge information. The new scheme is planned to be used in the BELLE experiment at the KEK B-Factory. We built a prototype Shaper/QTC board and examined the performance with a beam test. This new scheme worked successfully. We obtained the same spatial and dEdx resolutions as those using an ordinary TDC and ADC readout scheme.

Cathode image readout in the BELLE central drift chamber

Abstract We report on the design and construction of the cathode image readout section of the BELLE detectors central drift chamber. The cathode information is used for measurements of charged particle trajectory coordinates along the beam axis and the charged-track trigger. The performance is evaluated with cosmic rays using the BELLE standard readout electronics and software. The detection efficiency in nominal conditions is found to exceed 98% and the position resolution for normal incidence is about 350xa0μm, which satisfies the design goals of the BELLE detector.

Present status and beam-stability issues of the KEKB injector linac

The KEKB injector linac was completely upgraded for the KEK B-Factory (KEKB) project in March, 1998. Many difficulties have been overcome during the elaborate commissioning of the upgraded linac since the end of 1997. The 3.5-GeV positron and 8-GeV electron beams have been injected to the KEKB rings with good performance. Much effort has also been continuing to stabilize the intensity and quality of the beams. Some experimental results on the beam stability issues am shown together with the recent operation status in this report. A beam test on a new scheme of a two-bunch injection was started in order to increase the positron intensity since March, 2001.

Recent Progress at KEKB

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

Increase of positrons by a high-intensity two-bunch acceleration scheme at the KEKB linac

As the accumulation current of positrons increases in the KEKB ring, the injection time is becoming longer. It will thus be one of the most important issues affecting the accumulation of the integrated luminosity. As one of the steps, we introduced a high-intensity two-bunch acceleration scheme at the KEKB linac to intensify positrons by means of doubling the primary electrons. We recently obtained test results of 0.54 nC for the first bunch and 0.49 nC for the second bunch at the linac end. This scheme increased the positron intensity by nearly 65%. Since the linac frequency is not a harmonic number of the LER frequency, the best time interval between two bunches is 96.29 ns, corresponding to 49 LER-buckets. Even with this limitation, it is undoubtedly a very useful scheme for increasing the positron injection rate. The beam test results are described.

First measurements of beam backgrounds at SuperKEKB

Abstract The high design luminosity of the SuperKEKB electron–positron collider is expected to result in challenging levels of beam-induced backgrounds in the interaction region. Properly simulating and mitigating these backgrounds is critical to the success of the Bellexa0II experiment. We report on measurements performed with a suite of dedicated beam background detectors, collectively known as BEASTxa0II, during the so-called Phase 1 commissioning run of SuperKEKB in 2016, which involved operation of both the high energy ring (HER) of 7xa0GeV electrons as well as the low energy ring (LER) of 4xa0GeV positrons. We describe the BEASTxa0II detector systems, the simulation of beam backgrounds, and the measurements performed. The measurements include standard ones of dose rates versus accelerator conditions, and more novel investigations, such as bunch-by-bunch measurements of injection backgrounds and measurements sensitive to the energy spectrum and angular distribution of fast neutrons. We observe beam–gas, Touschek, beam–dust, and injection backgrounds. As there is no final focus of the beams in Phase 1, we do not observe significant synchrotron radiation, as expected. Measured LER beam–gas backgrounds and Touschek backgrounds in both rings are slightly elevated, on average three times larger than the levels predicted by simulation. HER beam–gas backgrounds are on average two orders of magnitude larger than predicted. Systematic uncertainties and channel-to-channel variations are large, so that these excesses constitute only 1–2 sigma level effects. Neutron background rates are higher than predicted and should be studied further. We will measure the remaining beam background processes, due to colliding beams, in the imminent commissioning Phase 2. These backgrounds are expected to be the most critical for Bellexa0II, to the point of necessitating replacement of detector components during the Phasexa03 (full-luminosity) operation of SuperKEB.

Low emittance lattice and final focus design for a SuperB project

Very low emittances and small beta functions at the interaction point(IP) are needed to achieve the design luminosity of 1036 cm-2 s-1 for a SuperB project. Two rings of 4 and 7 GeV have been designed with the same emittances and damping times. A new Final Focus section has also been designed to strongly squeeze the colliding beams both in the horizontal and the vertical plane at IP, while providing local correction of the large chromaticity and exploiting the large crossing angle and crab waist concepts. Lattice features and chromaticity correction schemes will be discussed here. Dynamic apertures, with damping wigglers similar to those of ILC, will also be presented.