Ultrafast electron diffraction<xref rid="cpb_27_7_076102_fn1" ref-type="fn">*</xref><fn id="cpb_27_7_076102_fn1"> <label>*</label><p>Project supported by the National Natural Science Foundation of China (Grant No. 11774409), the National Basic Research Program of China (Grant No. 2013CBA01501), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB16010200 and XDB07030300).</p></fn>

Ultrafast electron diffraction* *

Project supported by the National Natural Science Foundation of China (Grant No. 11774409), the National Basic Research Program of China (Grant No. 2013CBA01501), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB16010200 and XDB07030300).

Wang Xuan^{1, †}, Li Yutong^{1, 2, 3, ‡}

(color online) (a) Longitudinal phase space diagram for an electron bunch during its propagation. (A) The initial velocity distribution (shown in grey). (B) A velocity chirp is built-up in phase space (shown in red) due to space charge effect. (C) Distribution of velocity is flipped (shown in green) such that the bunch starts to compress. (D) The bunch reduces to its minimal duration (shown in blue). (b) Relative timing between the electron bunch and the transient electric field from the compressor, which can cause timing jitter if it changes randomly.