New method for high resolution analysis of betatron tune in a rapid cycling synchrotron or a booster ring

The betatron tune is one of the most important key parameters in an accelerator ring from the view point of beam dynamics and betatron resonance. Especially, the tune must control well in high intensity proton accelerator because high-intensity beam has the tune spread induced by space charge force. Therefore, it is very important to control the tune with high accuracy in high intensity ring. In a common method, the betatron tune is measured by analyzing the detected beam oscillation on a harmonic analysis and the measurement accuracy depends on frequency resolution. Therefore, it is important to analyze the data with a long detection time for high accuracy. However, a rapid cycling synchrotron and a booster ring cannot adapt the long detection time for high accuracy because the beam is quickly accelerated and the revolution frequency of the beam changes quickly. So, the tune accuracy is not improved by using a common method. In J-PARC 3-GeV rapid cycling synchrotron (RCS), we developed new method for high resolution analysis of the tune. In the new method, the disadvantage by the rapid acceleration turns to the advantage. As the result, tune accuracy of new method during acceleration was successfully improved from ±0.0132 to less than ±0.0005. So, we can control the tune tracking well during acceleration and this result leads the RCS to high-intensity. In this paper, we report new method for high resolution analysis of the betatron tune. Additionally, we mention the commissioning results and contribution for high-intensity beam. (author)