利用四极铁调制的方法可以改变工作点,测量工作点的改变,可以计算出四极铁位置的Beta函数值,这样测量得到的值是四极铁位置的平均Beta函数值.采用该方法在合肥光源(HLS)储存环进行了实验,四极铁电源电阻并联后,分流调制四极铁的电流,从而改变四极铁强度,对环上的30块四极铁进行Beta函数测量.以理论值为参考,对采用计算公式得到的结果进行了比较和分析,利用四极铁中心位置的理想Beta函数计算值和测量值作比较,结果表明:测量最大绝对差为2.741,平均绝对差为0.521;垂直方向的测量最大绝对差为1.711,平均绝对差为0.009,四极铁自身电流和分流电流的测量对Beta函数测量值误差的影响非常小.通过改进工作点测量系统,适当加大分流电流可以减小Beta函数测量误差.

A simple measurement of beta-function is to detect the shift in the betatron tune as the strength of an individual quadrupole magnet is varied. The beta-function value obtained is a mean value respect to the length of the quadrupole. The beta-function values at 30 quadrupoles in the HLS storage ring were measured by this means. The measurement results using different calculation formulas are compared with the ideal values. Error analysis is also given. Methods to improve the precision of the measurement are put forward for the advanced measurement.