• S. Döbert, A. Grudiev, G. Riddone, W. Wuensch, R. Zennaro
  CERN, Geneva
• C. Adolphsen, F. Wang, J.W. Wang
  SLAC, Menlo Park, California
• T. Higo, S. Matsumoto, K. Yokoyama
  KEK, Ibaraki

Prototype accelerating structures for the Compact Linear Collider (CLIC) are being developed and high-power tested in a collaboration between SLAC, KEK and CERN. Several undamped, low group-velocity and strongly tapered prototypes (of the so-called T18 design) have been operated above 100 MV/m average gradient at a very low breakdown rates. Recently two new structures with the same iris apertures but now including higher order mode damping waveguides in each cell (TD18 design) have been tested at SLAC and KEK. The damped versions could be processed to similar gradients but an increased breakdown rate was observed. The damping waveguides lead to a magnetic field enhancement in the outer diameter of the cells which results in increased pulsed surface heating. The maximum pulsed temperature rise is 80 deg at the design gradient of 100 MV/m compared to only 20 deg for the undamped version. The high-power tests of the two TD18 structures are analyzed with special emphasis on the influence on breakdown rate of the enhanced magnetic field and consequent increased pulsed surface temperature rise.

• K. Yokoyama, S. Fukuda, Y. Higashi, T. Higo, S. Matsumoto
  KEK, Ibaraki
• S. Calatroni, R. Santiago Kern, W. Wuensch
  CERN, Geneva
• C. Pasquino
  Politecnico/Milano, Milano

To investigate the breakdown characteristic related to the differences in purity and hardness, four types of oxygen-free copper (OFC) materials, usual class 1 OFC with/without diamond finish, 7-nine large-grain copper and 6-nine hot-isotropic-pressed copper, were tested with the DC spark test system at CERN. Measurements of beta, breakdown fields and breakdown probability are discussed followed by the surface inspection mostly with SEM on the tested materials.

• T. Kamitani, M. Akemoto, D.A. Arakawa, A. Enomoto, S. Fukuda, K. Furukawa, T. Higo, H. Honma, K. Hosoyama, N. Iida, M. Ikeda, E. Kadokura, K. Kakihara, H. Katagiri, M. Kikuchi, Y. Kojima, M. Kurashina, S. Matsumoto, T. Matsumoto, H. Matsushita, S. Michizono, K. Mikawa, T. Mimashi, T. Miura, H. Nakajima, K. Nakanishi, K. Nakao, Y. Ogawa, S. Ohsawa, T. Sanami, M. Satoh, T. Shidara, A. Shirakawa, T. Sugimura, T. Suwada, T. Takenaka, M. Tawada, Y. Yano, K. Yokoyama, M. Yoshida
  KEK, Ibaraki

The KEKB-factory will be upgraded for 40 times higher lumnosity (SuperKEKB). The injector linac is required to increase the beam intensities (e-:1nC -> 5nC, e-:1nC -> 4nC) and reduce the emittances (e-:300 -> 20 um, e+: 2100 -> 10 um ) for the SuperKEKB. A photo-cathode RF gun will be introduced to generate the high-intensity and low-emittance electron beams. A positron damping ring will be constructed to reduce the emittance. A new matching device (a flux concentrator or a superconducing magnet) and an L-band capture section will be introduced to increase the positron intensity. Beam line layout down to the damping ring will be rearranged to have sufficient beam acceptance considering the positron emitttance. This paper describes details of the upgrade scheme of the injector linac.

• S. Matsumoto, M. Akemoto, T. Higo, H. Honma, M. Ikeda, K. Kakihara, T. Kamitani, H. Nakajima, K. Nakao, Y. Ogawa, S. Ohsawa, Y. Yano, K. Yokoyama, M. Yoshida
  KEK, Ibaraki

In order to improve the positron beam intensity needed for super KEKB project, it was decided to replace the present S-band structures in the positron capture section by a new L-band (1298MHz) accelerator system. 　A 2m long TW structure of 12MV/m gradient is now under idesign process while a　40MW klystron will be delivered in summer. After the klystron testing, a single L-band accelerator unit will be constructed for the structure study. The study is scheduled in next spring to operate the structure under solenoidal magnetic focussing field.