Emittance measurement at KEK-ATF damping ring

In order to achieve an extremely low emittance down to /spl epsiv//sub y//spl sim/1/spl times/10/sup -11/ m-rad, the beam development has been continued at KEK-ATF for future linear collider. The emittance measurement in the damping ring is a key point to confirm the low emittance beam. The beam size measurement is done by SR interferometer using visible light (/spl sim/500 nm) at ATF damping ring. The measured beam sizes were already reached less than 14 /spl mu/m (vertical) acid 37 /spl mu/m (horizontal), respectively. The beta function was also measured by applying a perturbation on the quadrupole magnet. The dispersion function was measured by means of RF frequency modulation method. Combining these measured values, the emittance was measured as /spl epsiv//sub x/=1.8/spl times/10/sup -9/ m-rad, /spl epsiv//sub y/=6.1/spl times/10/sup -11/ m-rad. The measurement technologies are described.