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

在高性能双环正负电子对撞机(工厂)上，用KEKB和北京国际高能物理研究所的BEPC研究了快离子不稳定性(FII)和电子云不稳定性(ECI)这两种最严重的不稳定性。由于振荡频率与离子振荡的频率一致，我们认为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发。我们测量了沿着束团列车的每个束团的调谐，发现调谐沿列车增加并在某一值变得饱和，并且调谐的增加与束团列车的线电荷密度成正比。这有力地表明，束周围的电子云激发了束团内振荡，并导致了束流膨胀。在JFY2000中，我们将螺线管缠绕在KEKB正电子环上超过1200米。这些螺线管明显抑制了束流膨胀；然而，抑制并不像模拟预测的那么强。原因尚不清楚。由于KEKB在这些螺线管的作用下继续工作，束喷变得更弱了。截至2001年3月底，我们得到的发光率为3.2×10；lt；33；cm；-2；S；-1；-1，接近PEP-II记录的3.3×10；lt；33；-2&gt；S；-1&gt；的世界纪录，可能存在一定的擦洗作用。

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.