“…Therefore, it is necessary to study the actual structure of the electron beam to increase the overall efficiency of the TWT. Several different techniques have been developed to measure the electron beam, including pinhole, slit and optical image measurements [3][4][5][6][7][8][9], etc, and some test systems based on different methods have been built to diagnose the electron beams [10][11][12][13][14][15]. The slit method is applicable to the axially symmetric beams by means of integral equations [4], and the optical image method is usually applicable to high power beams (acceleration voltage U > 20 kV) [9].…”