Simulation study of resistive-wall beam breakup for ERLS

Resistive-wall beam breakup (RWBBU) due to the long-range transverse wake is studied with a developed simulation program. The simulation program is useful and essential for fully understanding the RWBBU behaviour in ERLs. The simulations demonstrate that the position displacement or orbit distortion due to the RW wake is proportional to the square root of time and the wake strength in the early stage of the RWBBU and they are consistent with the RWBBU equations. In case of the planned test ERL in Japan, the maximum position displacements increase up to 3% and 1% of the initial position offset with all the quadrupole magnets off and on at 77 mus. A small-gap insertion device(ID) duct increases the orbit distortion in downstream of the ID section, though a focusing effect due to the ID field may reduce it.