Cong-Feng Wu

Measurement for the kanthal alloy used for collinear load and the s-band load design

We have developed the method to determine the permeability and the electrical conductivity of the Kanthal alloy available. The alloy is coated inside the walls of disk-loaded cavities, which is used for the collinear load. The collinear load absorbs the remaining RF power over the last cells of the section while still accelerating the beam. Based on the experimental results of permeability and the calculated value of the conductivity, the computation study of the collinear load has been made by Microwave Studio. The attenuation in the collinear load is 16.02 dB.

Investigations of photonic band gap microwave-driven accelerating cavity

We report the calculation and cold test results for an 11.424 GHz photonic band gap (PBG) cell, which can be utilized as an accelerating cavity. Cold test results are compared with the theoretical design of the resonator. The S parameters and the field pattern were simulated for the PBG-based cavity by putting the six SiC rods, which are used as the microwave absorber, at the outer circle of the cavity instead of the six copper rods. The simulation results show that the higher-order-modes may be efficiently suppressed.

Model cavity investigations and calculations on hom for an x-band hybrid dielectric-iris-loaded accelerating structure

Some model cavities have been further developed and investigated for an X-band (f=9.37 GHz) hybrid dielectric-iris-loaded accelerating structure based on the calculated results about the effect of the dimension tolerance on the frequency. The dispersion curve fitted by using the measurement value is consistent with the one calculated. The r/Q values of the dipole modes have been calculated by Mafia code. The theoretical results show that the r/Q values of dipole modes for the new accelerating structure are lower than those for the iris-load accelerating structure.

Simulations for the advanced photonic band gap accelerating structure

Photonic band gap(PBG) accelerating structures have gained increasing attentions for the HOMs damping property. A cavity of advanced 2-D metallic PBG structure has been designed in order to improve the pulsed heating performance. Simulations and design of the couplers for the advanced PBG traveling wave accelerating structure is accomplished. A method to suppress the high order modes (HOMs) is proposed. The changes in the frequency caused by the radial movement of rods have also been studied for tuning.

The Studies of X-Band Hybrid Dielectric-Iris-Loaded Accelerating Structure

The dispersion property and the propagation characteristic of the accelerating mode (TM01mode) about a X-band (f=9.37GHz) hybrid dielectric-iris-loaded accelerating structure has been analysed and discussed by the field matching method and Mafia code respectively. The ones of the HEM11mode have also been calculated by MAFIA code. Based on the experimental results of the used dielectric (ceramic). Mafia code has been used to make the optimization design for the new structure. Some model cavities have been developed and measured. The experimental investigations show that the results are nearly agreement with the theory design.

Calculations and design of a third harmonic cavity for increasing the beam lifetime

Higher harmonic cavities are used widely in light sources to increase the bunch length and decrease the charge density. This approach may be adopted to increase the beam lifetime in HLS-II. The beam dynamics and bunch lengthening with a passive harmonic cavity are presented in this paper. The result shows the charge density is decreased greatly. A third harmonic cavity similar to the KEK-PF RF cavity for HLS-II is designed, in which the higher order modes are absorbed by SiC ducts and three couplers with rodshaped antenna.

Coupler design and test for X-band hybrid loaded circular waveguide accelerator

The coupler for X-band hybrid dielectric-metal disk-loaded circular waveguide accelerator was designed and tested. The S parameters versus the coupler cavity radius b, the iris aperture w and its thickness h have been simulated by Microwave Studioreg. The optimized reflection coefficient Sn being 0.01 was got at 9.372 GHz. The experiment result of the standing-wave ratio SWR of the coupling cavity being 1.03 was obtained at 9.372 GHz. The simulated results are accorded with the tested results.

Simulation on S-band alternating periodic structure

Simulations of the RF characteristic (dispersion curves, operating frequency, and electric field distributions) of the alternating periodic structure (APS) are given. The dispersion relations of APS are compared with the uniformly periodic structure (UPS). The above results are accorded with the tested results of the Toshiba Research and Development Center. The simulations make the tuning process of the APS very easy.

Research of metal-dielectric photonic crystal accelerating structures

In the design of high intensity rf accelerators, photonic crystal has been suggested to suppress unwanted high order modes (HOMs) and avoid rf breakdown. Base on the conception, we select a metal-dielectric (copper + sapphire) PBG based cavities(named with pillbox structures) to establish an overmoded photonic crystal accelerating structure which consists of dielectric rods and metal disks with irises. The band gap calculation for 2D triangular crystal lattice of dielectric rods has been performed with plane wave expansion method (PWM). From the results, we simulated the accelerator structures with Microwave Studio, and optimized the dimensions for the operating higher-order TM02-like mode approaching communication frequency at 9.37 GHz.The S-Parameters with the coupled probes was simulated at last.

Coupler design for x-band hybrid dielectric-iris-loaded accelerator

The coupler design for X-band hybrid dielectric-iris- loaded accelerator has been studied. Firstly, the S parameter versus the coupler cavity radius b, the iris aperture w and its thickness h has been simulated by Microwave Studio for the ordinary coupling cavity due to its simplicity. We have obtained the primary experiment result of the standing-wave ratio of the coupling cavity being 1.82. Secondly, the new coupler with the dual symmetric coupling ports , which first converts RF from TE to TM mode in a pure metal section and then a tapered transition section is added for high efficiency transmission to the dielectric accelerator section, has been calculated. The simulated results show that it is capable to convert the rectangular TE10 mode into circular TM01 mode with high efficiency.