Low emittance optics for PF-AR

PF-AR is a 6.5 GeV storage ring for the synchrotron radiation with the emittance of about 300 nmrad that is about two orders of magnitude larger than that of the present standard light sources. The injection energy was 3 GeV and the beam instability was so severe that we almost cannot change the optics and operating point from the original one designed in 1980s with keeping the injection and acceleration stability. A new 6.5 GeV full energy direct beam transport (BT) line was constructed and PF-AR started the user-run with this new BT from Spring 2017. The injection was very smooth with the weak beam instability compared to the case of 3 GeV and thus there is a new possibility to change the optics and operating point for the low emittance. In this presentation, we review the previous low emittance optics study in 2003 and the preparation status for the machine study with the new BT. (author)