Beam Intensity Upgrade of a Storage Ring by Curing Instabilities by Chromaticity Modulation and its Usage Test

束流的横向不稳定性是限制储存环束流的重要因素之一。色度调制是一种抑制横向不稳定性的方案，由首席研究员发明。由同步加速器频率调制的色度耦合了光束的同步加速器运动，并在束团内部引入了横向振荡的频率扩展，或电子感应加速器调谐的扩展。这种扩展抑制了聚束的相干振荡，以克服由不稳定性驱动的相干振荡的激发。八极磁体和反馈系统是通常用于抑制不稳定性的设备，但是在八极磁体下注入束本质上是困难的，并且反馈系统不能抑制在束团内部发生的单束团不稳定性，并且需要大量的工作来调谐。而色度调制则克服了这一缺点，我们将其应用于NewSUBRU储存环。5 kHz AC六极磁体，具有电容组的LC谐振器型电源，能够连续调谐驱动频率，研制了用于交流磁场的束管真空室和在交流六极磁铁段引入色散的晶格，束流实验表明相干振荡的阻尼得到了很大的增强，阻尼时间比原来缩短了一个数量级，小于1ms比辐射阻尼更大。束流实验还显示了对加速腔高阶模驱动的水平多束团不稳定性和束管宽带阻抗驱动的垂直单束团模耦合不稳定性的抑制，证明了色度调制对抑制横向不稳定性的有效性，并进一步提高了环流。

Transverse instabilities of beams are the one of the most serious factor that limits the beam current of storage rings. Chromaticity modulation is a scheme to suppress transverse instabilities and is invented by the head investigator.The chromaticity modulated by synchrotron frequency couples the synchrotron motion of a beam and introduces the frequency spread of the transverse oscillation, or the spread of betatron tune, inside of a bunch. This spread damps the coherent oscillation of the bunch to overcome the excitation of the coherent oscillation driven by instabilities. Octupole magnets and feedback systems are devices usually used to suppress the instabilities but injection of a beam under the octupole magnet is intrinsically difficult and feedback systems can not suppress the single-bunch instabilities that occur inside of a bunch and requires a large amount of work for tuning. However chromaticity modulation has no such shortage.We applied this scheme to NewSUBRU storage ring. A 5 kHz AC sextupole magnet, a LC resonator type power supply with capacitance bank which enables continuous tuning of the drive frequency, the beam pipe vacuum chamber for the AC magnetic field and a lattice to introduce dispersion at the AC sextupole magnet section were developed.The beam experiment showed the strong enhancement of damping of coherent oscillation and we obtained the damping time less than 1ms which is one order shorter than that of the radiation damping. The beam experiment also showed the suppression of the horizontal multi-bunch instability driven by a higher order mode of an acceleration cavity and suppression of the vertical single-bunch mode-coupling instability driven by broad-band impedance of a beam pipe.We proved the effectiveness of the chromaticity modulation to suppress the transverse instabilities and this scheme leads to further increase of the current of rings.