Development of a fast and high-resolution beam profile monitor with a laser wire target

超低发射度电子束的产生是实现第三代同步辐射光源、自由电子激光和/或高能电子直线对撞机的关键技术之一。本研究的主要目的是研制一种能对储存环中的小电子束尺寸进行定向测量的高精度束流轮廓监测仪。这种监视器是基于电子与激光线的康普顿散射，激光线是安装在光束中的一个细小的光目标。它是通过将激光注入法布里-珀罗光学腔来实现的。我们的主要研究成果概括如下：(1)研制了功率增益高达2000、激光束腰为11um的光腔。(2)成功地测量了ATF阻尼环在单束团模式下的电子束尺寸，并证明其垂直方向和水平方向的目标发射度分别为1.1×10~(-11)mrad和1.1×10~(-9)mrad。(3)我们还在多束团模式下测量了电子束尺寸，发现没有很大的束团-束团依赖关系。本研究建立了激光线束轮廓监测技术，有助于对超低发射度光束动力学的理解。

Production of ultra low emittance electron beams is one of the essential techniques in realizing third-generation synchrotron radiation light sources, free electron lasers 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 small electron beam sizes in a storage ring. This monitor is based on the Compton scattering of electrons with a laser wire, which is a thin light target installed in the beam. It is realized by injecting laser light into a Fabry-Perot optical cavity. We summarize the main results of this research below.(1) We developed an optical cavity with the power gain as large as 2000 and the laser beam waist of 11 um.(2) We successfully measured the electron beam sizes of the ATF damping ring operated in a single bunch mode, and demonstrated that it achieved the target emittance of 1.1x10^{-11} mrad in the vertical direction and 1.1x10^{-9} mrad in the horizontal.(3) We also measured the electron beam size in a multi-bunch mode, and found that there was no big bunch-to-bunch dependence. The present research established the techniques of the laser wire beam profile monitor and contributed to the understandings of ultra-low emittance beam dynamics.