Multipole Field Optimization of X-Band High Gradient Structure

The X-band constant gradient acceleration structure plays a crucial role in the VIGAS project. However, the presence of a multipole field component in the struc-ture’s coupler leads to an increase in ray bandwidth and a decrease in yield, ultimately affecting the quality of the generated rays. Through calculations, it has been determined that the quadrupole field component is particularly prominent in the original structure, ac-counting for 29.5% of the fundamental mode strength. Therefore, it is necessary to modify the cavity struc-ture of the coupler. By altering the shape of the cavity to two staggered circles, the objective of reducing the quadrupole field is achieved. The optimized quadru-pole field component now accounts for approximately 0.3% of the fundamental mode strength. Subsequently, the non-resonant perturbation method was employed to simulate and experimentally measure the magnitude of the multipole field component in the actual acceler-ation cavity.