No abstract

A novel design of a movable mask (collimator) for high-current accelerators is proposed. The mask head is supported by a ceramic rod to reduce interference with the beam. One side of the support is coated with a thin ( 1 m) conductive material to avoid extra charge up of the head. The head is also made of ceramics to avoid direct damage from an intense beam. To investigate the availability of the new movable mask, the rf properties, such as the impedances of trapped modes and the loss factors, were evaluated by simulation codes. The frequencies and the Q values of the trapped modes were also measured using a test model, and compared with calculated ones. Two trial modes for KEKB are being manufactured, and will be tested with beams next year.

Based on experiences in the precedent stainless steel case, a possibility of employing copper-alloy and aluminum-alloy Matsumoto-Ohtsuka (MO)-type ‰anges in a vacuum beam pipes for a particle accelerator is experimentally studied. They can mitigate the heating problems found in the case of stainless-steel ‰anges under high-intensity beams, and also simplify the manufacturing procedure of beam pipes. Copper-alloy ‰anges show a comparable vacuum sealing property to the stainless-steel one, and several beam pipes with the copper-alloy ‰ange has been successfully installed in the KEKB B-factory positron ring. The R&D on aluminum-alloy ‰anges has just started, and a promising result is obtained. Any coatings or treatments to improve the hardness of sealing part can be omitted if duralumin-series aluminum alloys are used. However, further detailed investigations are required about the hardness and stiŠness properties of the gasket and ‰ange materials before applying the ‰anges to the real machine.

No abstract

No abstract