Emittance measurement at KEK-ATF damping ring

In order to achieve an extremely low emittance down to ε_y~1×10^-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 (~500 nm) at ATF damping ring. The measured beam sizes were already reached less than 14 μm (vertical) acid 37 μm (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 ε _x=1.8×10^-9 m-rad, ε_y=6.1×10^-11 m-rad. The measurement technologies are described