Suwada T, Anami S, Chehab R, Enomoto A, Furukawa K, Kakihara K, Kamitani T, Ogawa Y, Ohsawa S, Oogoe T, Okuno H, Fujita T, Umemori K, Yoshida K, Hamatsu R, Sasahara K, Ababiy V, Potylitsyn A P, Vnukov I E
Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Jan;67(1 Pt 2):016502. doi: 10.1103/PhysRevE.67.016502. Epub 2003 Jan 16.
Intense positron sources are being widely investigated for the next-generation linear colliders and B factories. A new method utilizing an axially oriented crystal as a positron-production target is one of the bright schemes, since it provides a powerful photon source through channeling and coherent bremsstrahlung processes when high-energy electrons penetrate the target. A series of positron-production experiments with tungsten crystals hit by 4- and 8-GeV single-bunch electron beams were carried out at the KEKB 8-GeV injector linac. Three tungsten crystals with different thicknesses (2.2, 5.3, and 9.0 mm) and those combined with amorphous tungsten plates were tested on a precise goniometer. The positron-production yields were measured with a magnetic spectrometer in the positron momentum (P(e(+))) range from 5 to 20 MeV/c. The angle of the <111> crystal axis with respect to the electron-beam direction was controlled by measuring the relative intensities of the produced positrons as a function of the rotational angle of the goniometer. The results show that the enhancements of the positron yield from crystal targets compared to amorphous targets of the same thickness at P(e(+))=20 MeV/c are from 1.5 to 3.7 and from 1.8 to 5.1, depending upon the target thickness for 4- and 8-GeV electrons, respectively.
下一代直线对撞机和B工厂正在广泛研究高强度正电子源。一种利用轴向取向晶体作为正电子产生靶的新方法是其中一个亮点方案，因为当高能电子穿透靶时，它通过沟道效应和相干轫致辐射过程提供强大的光子源。在KEKB 8 GeV注入器直线加速器上，用4 GeV和8 GeV单束电子束轰击钨晶体进行了一系列正电子产生实验。在精密测角仪上测试了三种不同厚度（2.2、5.3和9.0毫米）的钨晶体以及与非晶态钨板组合的晶体。用磁谱仪在正电子动量（P(e(+))）范围为5至20 MeV/c内测量正电子产生率。通过测量所产生正电子的相对强度作为测角仪旋转角度的函数，来控制<111>晶轴相对于电子束方向的角度。结果表明，在P(e(+)) = 20 MeV/c时，与相同厚度的非晶靶相比，晶体靶的正电子产额增强分别为1.5至3.7和1.8至5.1，这取决于4 GeV和8 GeV电子的靶厚度。
