Study on beam instabilities at electron-positron colliders (factories)

利用KEKB和BEPC研究了高性能双环正负电子对撞机中最严重的快离子不稳定性和电子云不稳定性。在正电子环中，不仅观察到了偶极振荡，而且还观察到了垂直束流爆破。我们测量了沿着一个聚束串的每个聚束的调谐，发现调谐沿着聚束串沿着增加，并在某个值处变得饱和，并且调谐的增加与聚束串的线电荷密度成正比。在JFY 2000中，我们在KEKB正电子环上绕了1200米的线，发现了电子云在束团内的振荡。这些干扰明显抑制了波束放大;然而，这种抑制并不像模拟预测的那样强。原因尚不清楚。通过KEKB的连续运行，束流爆散变得较弱。到2001年3月底，我们测得了3.2×10^<33>cm^<-2>s^<-1>，接近PEP-Ⅱ观测到的3.3×10^<33>cm^<-2>s^的世界记录<-1>。

Study of fast-ion instability (FII) and electron cloud instability (ECI), which are most serious instabilities at high-performance, two-ring electron-positron colliders (factories) were investigate by using KEKB at KEK and BEPC at IHEP Beijing.In an electron ring, the growth of vertical dipole oscillation amplitued along a bunch train was observed by the use of a transient recorder. Since the oscillation frequencies coincided with those of ion oscillations, we believe that FII was detected.In a positron ring, not only dipole oscillations but also vertical beam blowup were observed. We measured the tune of each bunch along a bunch train and found that the tune increased along the train and became saturated at some value and that the increase of the tune was proportional to the line charge density of the bunch train. This strongly suggests that electron clouds around the beam excited intra-bunch oscillation and caused the beam blowup.In JFY2000 we wound solenoids over the KEKB positron ring over 1200 m. These solenoids clearly suppressed the beamblowup ; however, the suppression was not as strong as simulations predicted. The reason yet to be made clear. By continued operation of KEKB with these solenoids on, the beam blowup has become weaker. By the end of March 2001, we got a luminoity of 3.2×10^<33>cm^<-2>s^<-1>, which is close to the world record of 3.3×10^<33>cm^<-2>s^<-1> recorded at PEP-II.Some scrubbing effect is suspected.