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Description
This paper presents a comprehensive design study of the H⁻ injection line system for an 18 MeV compact high-current cyclotron. The injection line system, with a total length of 1310 mm, employs a configuration incorporating dual solenoids for transverse focusing and a buncher for longitudinal bunching. Beam transport design and space charge effect simulations were performed using specialized beam optics calculation software.Comparative analysis of buncher performance at 300 V and 500 V led to the selection of 500 V as the optimal operating voltage for longitudinal bunching. The influence of space charge effects at different beam currents (1mA, 3mA, 6mA) on beam envelope was systematically investigated under fixed solenoid strengths. Results demonstrate that while space charge effects significantly affect beam envelope, the 6mA condition remains within design specifications. Beam envelope matching across different space charge conditions was achieved by adjusting solenoid currents, resulting in a maximum envelope below 40 mm and an exit envelope under 20 mm. The normalized emittance after envelope matching reached maximum values of only 0.27365 mm·mrad and 0.27616 mm·mrad in the x and y directions, respectively, at 6mA operation. The optical system can maintain compact beam envelopes throughout transmission while ensuring proper focusing at the line exit. All results fully comply with initial design requirements, providing a reliable foundation for engineering implementation.
