The design study for low-Q IP-BPM

Beam position monitors (BPMs) with a resolution in a few nanometers range are required to control beams in the locations that are close to the interaction point (IP) of the international linear collider (ILC). ATF2 at KEK has considered as a test facility to investigate this requirement. In order to measure beam position stability at ATF2 final focus, a kind of IP-BPM has been developed at KEK and it has been tested in the ATF extraction line. We have designed an IP-BPM with lower Q-value than the IP-BPM in the extraction line in order to achieve smaller resolution. It enables easier separation of individual bunches in a multi-bunch signal. We have performed the design study for IP-BPM by using of the electromagnetic simulation program MAFIA and HFSS. The designed IP-BPM consists of one cell sensor cavity and one cell reference cavity. The results of the design studies showed signal decay time of 20 ns and the resolution of a few nm. We present the results of design studies in which include effects of common mode contamination in the IP-BPM, as well as preliminary test results on the proto-type IP-BPM.