Physical design of 2 MeV standing wave accelerating tube

In order to develop compact accelerators with small beam spot, a C-band 5.52 GHz 2 MeV SW accelerating tube is physically designed and studied, which operated in the π/2 mode. Not using any exterior focusing element，transverse emittance growth aroused from space charge effect is restrained efficiently by repeatedly bunching and utilizing dissymmetry field of first cavity. The accelerating tube consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163 mm，excited with 1 MW magnetron. In final dynamics simulation, 2 MeV 150 mA beam pulse current is obtained, and the capture efficiency is more than 30%. By means of nolinear Gauss fit on electron transverse distribution, the diameter of beam spot (Full Width at Half Maximum of density distribution) is about