Numerical analysis and design of collinear load for S-band linac based on FeSiAl material

Collinear load instead of traditional waveguide load is advanced for Linac miniaturization. In order to develop high power collinear load, an efficient microwave-absorbing material of FeSiAl is employed, meanwhile responding simulation design method is proposed in this paper. CST simulations demonstrate that the operation frequency of the cavity falls linearly with a rate of about −14.74 kHz/mm3 to the FeSiAl coating volume, while the quality factor appears inversely proportional and can drop to about 25. Cavity dimensions were adjusted to compensate the frequency shift from 2856 MHz. Orthogonal tests indicate that the real part of the permeability of FeSiAl notably affect the operation frequency of load cavities, while the imaginary part of the permeability acts on the attenuation much. Eventually based on uniform power absorption principle, a six-cavity collinear load was designed with one-way attenuation of −29.47 dB, and the detail parameters are presented.