Abstract
One of the latest problems in positron or proton accelerators is a single-beam instability due to an electron cloud around the beam. The seed of the electron cloud is the electrons emitted from the surface of beam chamber, which consist of electrons due to the synchrotron radiation (photoelectrons) and sometimes those multiplied by the multipactoring. Here a rough surface with a saw-tooth structure (saw-tooth surface) is proposed to reduce the electron emission from the surface of beam chamber. A new rolling-tap method is developed for this study to make the saw-tooth surface in a circular beam chamber with a length of several meters. The first experiment using a short test chamber at a photon beam line of the KEK Photon Factory verifies its validity, that is, the photoelectron emission from the saw-tooth surface reduces by one order of magnitude compared to the usual smooth surface. In the second experiment under a bunched positron beam in the KEK B-Factory, however, the electron emission is comparable to that of smooth surface and the behaviour is quite different from the previous one. The reason is that the successive bunched beam excites the multipactoring of electrons and the decrease of the photoelectron emission by the saw-tooth surface is wiped out. The saw-tooth surface will be effective to reduce the electron emission under the situation with external magnetic fields or without strong beam fields where the electron multipactoring hardly occurs.
