The wire scanners are used for a measurement of the very small beam size and the emittance in Accelerator Test Facility (ATF). They are installed in the extraction beam line of ATF damping ring. The extracted beam emittance are ex=1.3x10-9 m.rad, ey=1.7x10-11 m.rad with 2x109 electrons/bunch intensity and 1.3GeV energy. The wire scanners scan the beam by a tungsten wire with beam repetition 0.78Hz. The scanning speed is, however, very slow(~500um/sec). Since the extracted beam is quite stable by using the double kicker system, precision of the size measurement is less than 2um for 50 - 150um horizontal beam size and 0.3um for 8 - 16um vertical beam size. The detail of the system and the performance are described.
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