INJECTOR LINAC UPGRADE FOR SuperKEKB

2018

KEK injector linac has delivered electrons and positrons for particle physics and photon science experiments for more than 30 years. It was upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB, in order to increase our understanding of flavor physics beyond the standard model of elementary particle physics. SuperKEKB energy-asymmetric electronpositron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. The electron beam is generated by a new type of RF gun, that provides a much higher beam current to correspond to a large stored beam current and a short lifetime in the ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced from 2000 μm to 10 μm in the vertical plane by introducing a damping rin...

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.

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.

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.

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.

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...

Proceedings of International Conference on Particle Accelerators

A. Electron Gun The injection system (pre-injector) of the KEK 2.5GeV linac has been upgraded so that we can investigate intense beam acceleration for the KEK B-factory project. It requires intense beams to achieve a short injection time in practice. An outline of the new pre-injector and its performance is given. We changed the electron gun to a newly designed one, which is under operation at 190 kV. A ceramic insulator was changed from one 130 mm long with ICF-203 flanges to at one of 300 mm long with ICF-253 flanges. The cathode is a commercially available one (EIMAC Y-796). B. Bunching System

2013

After a decade of successful operation at KEKB a new asymmetric electron/positron collider, SuperKEKB, is being constructedupgradingKEKB. It aimsata luminosityof 8 × 10 35 cm −2 s −1 , 40-times higher than that of KEKB, in orderto studythe?avorphysicsof elementaryparticlesfurther, by mainly squeezing the beams at the collision point. The injector linac should provide high-intensity and lowemittance beams of 7-GeV electron and 4-GeV positron by newly installing a RF-gun, a?ux concentrator,and a damping ring with careful management of emittance and energy spread to be 20 mm.mrad and 0.1%. It should also perform simultaneous top-up injections into four storage rings by pulse-to-pulse beam modulations not to interfere between three facilities of SuperKEKB, Photon Factory and PF-AR. This paper describes the injector design decisions and present status of the construction. SuperKEKB will be commissioned within FY2014.

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.