X-band Hybrid Dielectric-iris-loaded Accelerator Investigations

The development of the linac in the world and some advanced accelerator concepts are described in the thesis.The accelerating structure based on dielectric is emphasized here.The hybrid dielectric-iris-loaded structure may have lower ratio of peak surface electric field at the iris to axial accelerating electric field than the one of the iris-loaded waveguide structure by optimizing the geometric parameters,while r/Q of the new structure being comparable to iris-loaded accelerating structure.With the help of MAFIA code,MATLAB code,Microwave Studio and PAMELA code,a small and high accelerating gradient x-band hybrid dielectric and iris loaded travelling wave electron linac was theoretically studied.The length of accelerator tube is 1.47m.The maximum accelerating gradient is 45MV/m.The beam energy is 32MeV.The capture efficiency is about 40%,the energy spread is about 0.5%and the beam emittance is about 5.7πmm·mrad under the conditions of the beam current being 100mA and the electron gun voltage being 50KV.The choice of appropriate dielectric is crucial for the design of the new accelerating structure.The dielectric constant(εr) and dielectric loss(ranδe) of the composition Forsterite(Mg,Silicate) made in USA are measured using cavity perturbation method.The results show that:the values of permittivity vary slowly when the frequencies are near to 9.37GHz,the dielectric constant is 6.29 and the dielectric loss is 0.000195,the consistency of the dielectric is good.The configuration is tested by XFS,XPS and permittivity of the dielectric is measured using cavity perturbation method after annealing.The results show that the performance of the dielectric is steady on the whole.Because of high hardness and brittleness of the dielectric,a lot of machining technology and methods are attempted.Through large numbers of experiments, some model cavities have been developed successfully at the frequency of 9.37GHz and the Q value of 1148.6 is obtained after brazing in a hydrogen furnace.The RF coupler is an important component for an accelerator structure.Originally, using the dielectric made in China whose dielectric constant is 5.81,the coupler was simulated with the help of the Microwave Studio(MWS) T-Domain Solver.It took one much more time to simulate.The experimental results show that the actual value of the coupler aperture is very different from the theoretical value.A novel calculation method based on the Kyhl method is obtained with F-domain solver of MWS for the design of the coupler.The calculation method can save much more time under the same precision than other methods.In addition,it is interesting that large numbers of calculations for the new structure show that the position of the plunger should be apart from the coupler cavity centre(3mm forward the electric gun) for detuning.To iris-loaded waveguide structure,the position is in the centre of the cavity.According to above calculated results,the coupler was developed.The experimental results show that the SWR＜1.02 at the operation frequency(f=9.37GHz) and SWR＜1.10 within the bandwidth of 20 MHz.The experiment results are accorded with the calculating results after few processes.On the other hand,the brazing technics of the dielectric loaded and iris-loaded waveguide structure are attempted firstly.The electric field in the axis and the phase shift of the accelerating mode are also investigated.In order to eliminate parasitic dipole modes and to minimize beam perturbations that could lead to beam breakup effects in the accelerator,the dielectric loaded circle waveguide accelerating structure(especially the coupler) is investigated theoretically. The coaxial coupling approach employs a double-input design to symmetrize the coupling regions.At last we developed a new method using coaxial resonant cavity to determine the high frequency permeability of the Kanthal alloy available for collinear load.Many measurement methods reported are not fit for the alloy.The relative permeability of 2.58 is obtained by this method and the conductivity of sprayed material ofσ= 8978.27mhos/m is got.Based on the results of the permeability and conductivity,the computer simulation for the design of the collinear load was made by Microwave Studio.