Physics Design of a 200-MeV Electron Injector Linac With a Thermionic Electron Gun for the Korean Fourth-Generation Storage Ring Light Source

This study presents a comprehensive physics design and optimization investigation of an electron injector system for the Korea fourth-generation storage ring (Korea-4GSR) light source with a target operating energy of around 200 MeV. The Korea-4GSR construction project is currently underway and expected to continue until 2027. The injector system comprises a thermionic dc gun, buncher systems, and four accelerating cavities (ACs). The thermionic gun was designed to achieve a combination of low emittance and high current. Through beam dynamics simulations, we investigated different types of buncher and ACs. Optimization was performed on the geometries and electromagnetic properties of each cavity type to enhance beam bunching and acceleration. Nonlinear optimization techniques were employed to maximize transmission efficiency by adjusting solenoidal magnet strengths and minimize energy spread by optimizing RF input phases and cavity positions. Our results demonstrated a transmission efficiency of 98.71%, an rms energy spread of 0.54%, a bunch length of 4.11 ps, and an normalized rms transverse emittance of 3.2219 mm
$\cdot $
mrad, meeting the design requirements of the Korea-4GSR injector system.