• F. Klarner, O. Boldt, W. Hillert
  ELSA, Bonn
• S. Aderhold
  DESY, Hamburg

Since 1966 a Varian factored injector is in use at the accelerator complex of the University of Bonn serving several experiments to investigate the subnuclear structure of matter. This injector will have to be replaced for several reasons. The new injector will operate in a single bunch mode of 2 A beam current and is currently under construction. Also a 2 μs long pulse mode of 500 mA beam current will be available for ordinary accelerator operation for hadron physics experiments. Produced by a pulsed thermionic 90 kV gun, compression of the pulses is achieved by a 500 MHz prebuncher as well as one β-matching travelling wave buncher running at the linac frequency of 3 GHz. The injector has been designed and optimised using the software package EGUN and numerical simulations based on the paraxial differential equations. The single bunch mode will allow to investigate single bunch instabilities within the Helmholtz alliance "Physics at the Terascale".

• Y. Ogawa, M. Yoshida
  KEK, Ibaraki

The KEKB linac continuously injects 8 GeV electron and 3.5 GeV positron beams into the KEKB rings: HER(high energy ring) and LER(low energy ring). The energy spread of the 8-GeV electron beam, which is accelerated to an 1.7 GeV 180-degree arc section and reaccelerated after this arc to a final energy of 8 GeV, is optimized by adjusting rf acceleration phases so as to assure efficient injections. When rf phases are slightly changed or drifted for some reasons, the beam not only shows larger energy spreads but also indicates two clusters on a beam profile monitor located at large energy dispersions. In this connection, a longitudinal beam profile was measured after the arc section with a streak-camera system utilizing an OTR(Optical Transition Radiation) bunch monitor. The observed bunch shape clearly shows a two-microbunch structure, suggesting that it could be generated in the arc section. Various experimental data as well as some CSR-related speculations are presented.

• C. Christou, V.C. Kempson, S.J. Singleton
  Diamond, Oxfordshire

Several modifications have been made to the 100 MeV Diamond Light Source pre-injector linac since initial commissioning in 2005 to improve beam stability and reliability and to increase the scope of operation of the system. Stability enhancements include tighter thermal control of low-level rf electronics, and a modified timing system for gun and linac operation. The linac has been optimised for multibunch filling of the storage ring and for single-bunch top-up operation with gun charge and timing determined by the state of the storage ring fill. Low-energy beam generation has been studied for fault-mode operation using one of the two rf stations, and a study of the options available for Diamond based on routine operation in this mode has been carried out. A summary of operational experience is presented, together with options for future development

• G. Isoyama, S. Kashiwagi, R. Kato, M. Morio, S. Suemine
  ISIR, Osaka

Funding: This research is partly supported by the accelerator support program to universities conducted by the High Energy Accelerator Research Organization in Japan.
The 40 MeV L-band electron linac at the Institute of Scientific and Industrial Research, Osaka University is operated for joint-use in Osaka University. It is equipped with a three-stage sub-harmonic buncher (SHB) system consisting of two 108 MHz and a 216 MHz rf cavities to produce a high-intensity single-bunch beam. They were quarter-wavelength coaxial cavities made of a clad plate of copper on stainless steel and were inefficiently cooled with water flowing through a pipe wound on their outer surfaces made of stainless steel. We have renewed the cavities with new ones made only of oxygen-free copper to solve the problem. We made physical design and basic mechanical design of the new rf cavities by ourselves by taking a mechanical design of the SHB cavity of the electron-positron linac at KEK, Japan as a model. Special care was devoted in the mechanical design to cool the most part of the cavities directly with water instead of relying on heat conductivity in copper so that they are stable in regard to temperature. They have been installed in the linac and have been working well in expected performance. We will report details of design and fabrication of the new SHB cavities.

• F. Wang, C. Adolphsen, J.W. Wang
  SLAC, Menlo Park, California

Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
A 5-cell, normal-conducting, 1.3 GHz, standing-wave cavity was built as a prototype capture accelerator for the ILC positron source. Although the ILC uses predominately super-conducting cavities, the capture cavity location in both a high radiation environment and in a solenoidal magnetic field requires it to be normal conducting. With the ILC requirements of relatively long beam pulse on-time (1 msec at 5 Hz) and high gradient for efficient positron capture (15 MV/m), achieving adequate cavity cooling to prevent detuning was challenging. This paper presents the operational performance of this cavity including its breakdown characteristics as a function of gradient, pulse length and solenoidal magnetic field strength. In addition, these results are compared with those from other normal-conducting cavities at various frequencies