Development of a laser wire beam profile monitor

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Production of ultra low emittance electron beams is one of the essential techniques in realizing third-generation synchrotron radiation light sources (SOR), free electron lasers (FEL) and/or high-energy electron linear colliders. The main purpose of the present research is to develop a precision beam profile monitor which can directory measure their electron beam size. Specifically, the monitor under development must be able to measure the electron beam profile in an ATF damping ring at KEK.Most important points in the project are (1) to realize a laser wire target that satisfies needed properties, and (2) to install it in the damping ring.First of all, we successfully developed a Fabry-Perot optical cavity with a beam waist of 15 μm and finess of 321. Having judged that the cavity above was good enough, we then installed it in the damping ring, and measured actual beam size or emittance. We found that the beam size was σ_b=9.8±1.0μm, consistent with the designed value. This has proved that the beam emittance in the ATF damping ring is lowest among the world's various machines. We further improved the cavity, and measured the emittance in search of possible current dependence. The crucial point in this measurement is to establish Toucheck effect, if present. Publication of the results is under way. In conclusion, we successfully developed the laser wire beam profile monitor with needed properties.