Study of initial stages of antiproton trapping processes

将5.9 MeV/u的反质子注入并捕获到3.5T的2m Penning陷阱中，然后电子冷却到几eV。研究发现，从10^~(-9)Torr到10^~(-8)Torr的外真空度对陷阱中反质子的寿命没有太大影响，这表明慢反质子进入原子轨道的捕获截面可能不同于所谓的朗之万截面，这对于气态靶的实验是一个好兆头，因为在那里需要强大的差动泵浦系统。然后研究了从陷阱中提取慢反质子的方案，构建了一个径迹探测器来确定所提取的反质子的湮没位置。为了实现五个数量级的差动抽气，研制了由两个涡轮泵、一个潜能泵和一个超高真空离子泵组成的差动抽气级。在此基础上，进行了多个Einzal透镜在不同磁场下的大尺度轨迹模拟，证明了上述结构可以实现合理的输运。用石英片和高灵敏度的CCD相机相结合的方法观测了被提取的反质子束的光斑大小，发现被提取的反质子的直径约为3 mm。

Antiproton beams of 5.9MeV/u are injected and trapped into a 2m Penning trap of 3.5T,and then electron-cooled down to a few eV.It is found that the lifetime of antiprotons in the trap does not depend very much on the outer vacuum from 10^<-9> Torr to 10^<-8> Torr, which indicates that the trapping cross section of slow antiprotons into atomic orbitals may be different from the so-called Langevin cross section, which is a good sign for experiments with gaseous targets, where powerful differential pumping systems are essential. Then extraction schemes of slow antiprotons from the trap have been studied constructing a track detector to determine the anihilation position of extracted antiprotons. In order to realize a differential pumping which amounts to five orders of difference, a differential pumping stage consisting of two turbo pumps, a sublimaion pump, and an ion pump for ultra high vacuum were prepared. Further, a large scale trajectory simulations including several Einzal lenses under varying magnetic field were performed, which proved that a reasonable transportation is possible with the above configurations. Spot sizes of extracted antiproton beams were observed employing a combination of a quartz disc and a high sensitivity CCD camera, which revealed the diameter of extracted antiprotons are about 3mm.