High-Intensity and Low-Emittance Upgrade

2010

In the forthcoming upgrade of the KEK-B factory to SuperKEKB, beam currents in the storage rings will be doubled and beam lifetimes will be ten times shorter. To make up for rapid decrease of the stored currents, several times higher linac beam intensities are required both in electrons and positrons. To achieve extremely high luminosity in the SuperKEKB, beam emittance has to be very low. Emittance of injected beams from the linac should be reduced to be five times smaller for electrons and two hundred times smaller for positrons compared to those of KEKB. To realize these low-emittance and high intensity beams from the linac, the electron pre-injector will be upgraded with a new electron-gun, the positron capture section will be upgraded for higher positron intensity and a positron damping ring will be introduced to make a positron emittance sufficiently small. This paper reports on design considerations in the linac upgrade for SuperKEKB.

2012

The SuperKEKB is now in a construction stage. The injector linac should be upgraded for realizing the 40times higher luminosity than that of KEKB. This requires both bunch charge increase and reduction of beam emittance. All of the relevant hardware designs for the injector system are being finalized now to meet the commissioning of the ring by the end of 2014. In the present paper is briefly reviewed the overall progress of such design decisions and hardware developments in the last two years. A perspective towards the commissioning is also presented.

Progress of Theoretical and Experimental Physics, 2013

The KEKB injector linac has been continuously improved to enhance the stability of many devices and the efficiency of beam operation. These improvements include the development of the new C-band accelerating structure, pulse compressor, klystron, rf window, compact modulator, and the new positron production target using crystalline tungsten. We have also achieved two-bunch beam acceleration, the development of an energy spread monitor, a safety system upgrade, and an event-based timing and control system. These developments and practical applications for advanced linac beam handling result in the success of the simultaneous top-up injection among the three independent storage rings. This result greatly improves the integrated luminosity and the operation stability of the KEKB rings.

2015

The electron / positron injector linac at KEK has injected a variety of beams into the electron accelerator complex of an asymmetric collider and light sources for particle physics and photon science experiments for more than 30 years. The beam property of electrons and positrons varies in energy from 2.5 GeV to 7GeV and in bunch charge from 0.2 nC to 10 nC, and their beam emittance and stability requirements are challenging dependent on the injected storage rings. They have to be switched by pulse-to-pulse modulation at 50 Hz. The emittance control is especially crucial to achieve the goal at SuperKEKB and is under development. The beam energy management becomes more important as it affects all of the beam properties. Beam acceleration provided by 60 high-power microwave stations should be properly arranged considering redundancy and stability. Thus, the equipment controls are also restructured in order to enable the precise control of the beam properties, based on the synchronized...

2000

A high-intensity, two-bunch acceleration scheme in the primary electron beam for positron production has been introduced at the KEKB linac for doubling the positron injection rate to the KEKB ring. The KEKB linac has until now injected single-bunch positron beams with an injection rate of about 1.4 mA/s (50 Hz) into the KEKB ring, requiring several minutes of topping-off time.

2016

The Phase I beam commissioning of SuperKEKB started in this February. The injector linac has successfully delivered the electron and positron beams to the SuperKEKB main ring. The linac beam studies and subsystem developments are also intensively going on together with the daily normal beam injection to both ring s of the SuperKEKB and two light sources. The main new significant subsystems are a positron damping ring, a positron capture system, a pulsed magnet, and a low emittance photo-cathode rf electron source. In this paper, we report the present status of Phase I beam commissioning. In addition, the commissioning plans of Phase II and Phase III are also described.

2015

Toward SuperKEKB project, the injector linac upgrade is ongoing at KEK in order to deliver the low emittance electron/positron beams with the high intensity and small emittance. In the September of 2013, the injector linac commissioning has started. In this presentation, we will describe the commissioning status and plan of SuperKEKB injector linac.

2012

The SuperKEKB project requires a positron and electron collider with a peak luminosity of 8 × 1035 cm−2 s−1. This luminosity is 40 times that of the KEKB B-factory, which operated for 11 years up to 2010. SuperKEKB is an asymmetry-energy and double-ring collider; the beam energy of the positron (LER) is 4GeV and that of the electron (HER) is 7GeV. An extremely small beta function at the interaction point (IP) and a low emittance are necessary. In addition, in order to achieve the target luminosity, a large horizontal crossing angle between two colliding beams is adopted, as is a bunch length much longer than the beta function at the IP. This method is called the “nano-beam scheme”. The beam–beam parameter is assumed to be similar to KEKB, the beta function at the IP is 1/20, and the beam currents are twice those of KEKB in the nano-beam

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001

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 are 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.

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001

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.