Online Measurement of Electrode Gains for Stripline Beam Position Monitor in the HLS II Storage Ring

ßπThree axially symmetric stripline beam position monitors were installed in the HLS II storage ring and each stripline BPM was machined with button BPM together. Due to mechanical errors of stripline BPM, differences in electrode gains will lead to measurement error for beam position and mutual coupling between beam horizontal position and vertical position. So it is very important to calibrate electrode gains for axially symmetric BPM. A method was proposed to calibrate electrode gains of this kind of BPM. This method is suitable for all axially symmetric BPMs, whether stripline BPM or button BPM. The online calibrated gains were compared with offline calibrated gains and the results have shown that online and offline calibrated electrode gains were basically consistent. INTRODUCTION Hefei Light Source II (HLS II) is a second generation Light Source[1]. From the beginning of 2016, HLS II has entered normal operation stage. Some parameters for the HLS II storage ring are shown in Table 1. BPM usually used in the storage ring is button BPM, but in order to measure some parameters based on stripline BPM, three stripline BPMs were still installed in the HLS II storage ring. Each stripline BPM was machined with button BPM together to save space[2]. The cross section of the stripline BPM is shown in Fig. 1(a) and site installation map for one stripline BPM is shown in Fig. 1(b). In this paper, a method was proposed to calibrate electrode gains of axially symmetric stripline BPM and the results between online and offline calibrated gains were compared. Specific details will be described in the next section. ONLINE MEASUREMENT OF ELECTRODE GAINS FOR AXIALLY SYMMETRIC STRIPLINE BPM As mentioned in the abstract, differences in electrode gains of BPM can lead to many measurement errors for beam parameters, so measurement of electrode gains for BPM is very important. For mirroring symmetric BPM, electrode gains of BPM was measured online and offline by D. L. Rubin[3] et al. For axially symmetric BPM, electrode gains of BPM was measured offline in [4]. We proposed a method to online measure electrode gains of axially symmetric BPM. Specific method and calibrated results are described in detail. 41.72 78.8 16 40 electrode(1.5)