介绍了修正三梯度法的原理和利用该方法测量发射度的实验装置.编写了基于束包络方程的数值拟合程序,并进行了模拟计算.用修正三梯度法对3.5MeV注入器出口处脉冲电子束的发射度做了时间分辨的测量.结果表明,当空间电荷力不可忽略时,该注入器输出的电子束脉冲期间中间部分束的发射度为1040π·mm·mrad.

Modified three gradient method is a method to measure beam emittance developed from three gradient method which has been widely used in beam diagnostics. Beam radius' evolution versus focusing current can be fitted by a cross-over curve calculated from the K-V envelope equation through which the cross-over curve depends on beam radius, divergence in the initial plane and beam emittance. An approximation of the emittance can be got by the fitting program. In this paper beam radius under different focusing current was measured with Cerenkov radiation method; Time-resolved beam profile was recorded by a streak camera; A numerical fitting program, based on the K-V equation, was developed; Influence of beam radius and divergence in the initial plane and emittance on the cross-over curve were studied through simulation; Time-resolved emittance of the pulsed electron beam produced by a 3.5MeV injector was measured and the results are presented. With the presence of space charge, beam emittance in the midst of the pulse is about 1040π·mm·mrad.