In the practical measuring process of beam emittance, X-ray produced by external electricity current and some beam particles hitting on the screen affects the stability of beam. The influence of external electricity current is called forbackground noise, and the influence produced by some beam particles hitting on the screen is called mutation noise. On the foundation of simulating to uninterferential two dimension transverse-phase-space density by computer and investigating the accuracy of measurement of CT method measure beam emittance in detail, we simulate the interferential two dimension transverse-phase-space density by computer and discuss the reconstruction accuracy influenced by background noise and mutation noise in detail. Results show that in the measuring process of CT beam emittance, the reconstruction accuracy is high forbackground noise but lower for mutation noise and the outline of the original graphics still can be seen although they have been disturbed. Therefore, technique of CT method measure beam emittance is appropriate for practical measurement.%束流发射度的实际测量过程中,外加电流和个别束流粒子打到荧光靶上产生X射线对束流稳定性产生一定影响.外加电流产生的影响称为本底噪声,个别束流粒子打到荧光靶上产生X射线构成的影响称为突变噪声.利用计算机对未受干扰的二维相空间密度分布函数进行模拟,在详细考察CT法测束流发射度的测量精度的基础上,对受干扰后的二维相空间密度分布函数进行计算机模拟,计算并讨论本底噪声和突变噪声对重建图像精度的影响.模拟结果表明:利用CT法测束流发射度的过程中,对于有本底噪声干扰的情况,该方法的重建精度很高；对于有突变噪声干扰的情况,该方法的重建精度相对前者低,图形出现一些干扰,但仍可以看出原始图形的轮廓.CT法测量相空间束流发射度技术适用于束流的实际测量工作.
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