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

梁的横向不稳定性是限制存储环梁电流的最严重因素之一。色度调制是一种抑制横向不稳定性的方案，是由首席研究员发明的。同步加速器频率调制的色度与光束的同步运动耦合，并引入了束内横向振荡的频率传播，即电子加速器调谐的传播。这种扩散抑制了束的相干振荡，克服了由不稳定性驱动的相干振荡的激发。八极磁体和反馈系统通常用于抑制不稳定性，但在八极磁体下注入光束本质上是困难的，反馈系统不能抑制单束不稳定性，而单束不稳定性发生在一束内部，需要大量的调谐工作。然而色度调制却没有这样的缺点。我们将该方案应用于NewSUBRU存储环。研制了5 kHz交流六极磁体、带连续调谐驱动频率电容组的LC谐振式电源、用于交流磁场的束流管真空室和在交流六极磁体部分引入色散的晶格。光束实验表明，相干振荡的阻尼得到了较强的增强，阻尼时间小于1ms，比辐射阻尼时间短一个数量级。光束实验还表明，该方法可以抑制高阶加速腔驱动的水平多束不稳定性，也可以抑制由束管宽带阻抗驱动的垂直单束模耦合不稳定性。我们证明了色度调制对抑制横向不稳定性的有效性，该方案导致环电流的进一步增加。

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.