Optics Measurements at SuperKEKB Using Beam Based Calibration for BPM and BBA

The beam-based calibration (BBC) technique for BeamPosition-Monitor (BPM) is applied in order to establish reliable optics measurement in SuperKEKB. A response model between beam position, charge and output signals of the BPM electrodes are introduced to calibrate the relative gain of the BPM electrodes (BPM Gain Calibration, BGC). The gains are adjusted by total squares fitting so that the model reproduces the measured BPM signals. The Beam-Based Alignment (BBA) is also performed to determine the magnetic center of a quadrupole. Using BGC and BBA, the performance of the BPM system and optics correction are successfully improved. This talk presents what we experienced in SuperKEKB so far focusing on beam optics measurement and some details on the beam-based calibration scheme for BPM system. INTRODUCTION SuperKEKB [1] is an electron-positron double ring collider and aiming to open up new luminosity frontier. The target peak luminosity of 8×10cms is 40 times higher than that achieved by the preceding project, KEKB [2]. SuperKEKB consists of electron (HER) and positron (LER) storage rings with an injector linac and a newly constructed positron damping ring. The design concept is based on the nano-beam scheme [3], in which both beams are squeezed to nano-scale sizes and collided with a larger crossing angle at the interaction point (IP). The key changes of machine parameters from KEKB are 2 times higher beam current, 1/20 times smaller vertical betatron function at the (IP). Low emittance tuning (LET) is essential for the nano-beam scheme as well as squeezing the betatron function. The SuperKEKB commissioning has started in 2016 after over 5 years of the upgrade work. The initial beam commissioning named Phase 1 [4] started on 1st February 2016 and finished on 28th June 2016. The final focusing quadrupole magnets (QCSs) for beam collision is not installed in Phase 1. The Phase 1 operation was devoted to the vacuum scrubbing and the basic setup of operating system. After installation of QCSs, the second beam commissioning (Phase 2) started on 19th March 2018 and finished on 17th July 2018 [5]. The first beam collision was observed at 26th April 2018. The 3rd beam commissioning phase (Phase 3) is started on 11th March 2019 [6]. Calibration of the BPM system is a key issue for better control of beam orbit and optics. We employ the BBC technique to the BPM system as at KEKB [7]. In BBC, both the relative gain of the BPM electrodes and the relative offset ∗ hiroshi.sugimoto@kek.jp Transmission line 2!