Abshuct-The behavior of multipactoring electrons in anS-band pillbox RF window used in the KEK electron linac was investigated. The electric field distributions in the pillbox were calculated using the MAFIA code. The trajectory of emitted electrons to the surface of an alumina window disk in the calculated electric field was simulated. The energy deposition distribution of electrons impinging on the alumina disk was also obtained. The results agree well with the discoloring patterns observed for alumina disks after RF operation. This shows that the discoloring can be explained in terms of the bombardment of single-surface multipactoring electrons. Knowledge concerning the electric field distribution and the behavior of multipactoring electrons in the pillbox RF window will be useful in designing RF windows from an electrical point of view.

In the KEK B-Factory plan, e+/e-collider rings with 3.5-GeV positrons and 8-GeV electrons are being considered, and fullenergy injection from the existing linac is required. The accelmtion energy of the linac must be upgraded from 2.5 to 8 GeV. The most effective way has been searched from several pomts of view, such as the beam quality, ease of beam handling, and construction. This article describes the basic plan of the energy upgrade and recent propss regarding this P r o j e c t

Thin films of TiN having low secondary electron emission (SEE) yields are coated on alumina rf windows in order to suppress the occurrence of multipactor. It is necessary to form films with a proper thickness in order to obtain a sufficient reduction of SEE as well as to avoid any excessive ohmic loss in conductive TiN films. For an optimization of the film thickness on an alumina surface, measurements of the SEE coefficients, and ohmic losses in the rf (S-band) field were carried out. High-power examinations of the coated windows were also performed. The results show that TiN films with a thickness of 0.5 nm or greater on alumina ceramics have SEE coefficients of less than unity at an incident energy of 10 keY. High-power tests have revealed that the "going away" of TiN films is probably due to excessive ohmic losses taking place when the thickness is greater than 1.5 nm. It is concluded that optimized film thickness for window coatings is 0.5-1.5 nm.

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