【摘要】 为了在电子直线加速器中，抑制束流爆破效应和尾场效应，中国原子能科学研究院在ＦＥＬ研究中计划采用３π／４模行波拱型腔结构，并用变分法理论设计了３ｍ长等梯度加速段，同时用铝制试验腔验证了理论设计。更多还原

【Abstract】 AbstractIn order to improve the beam quality and reduce the BBU effect and wake field effect by highbeam current in the electron linear accelerator for FEL research, an accelerator structure with aconstant gradient travelling wave（TW）,3π/4-mode is used, which has a coved cavitiesand extended nosecones.A variational method tO calculate this coved cavity Structure is uscd in our work￣[4].The resultsare similar to that of Boeing Aeros pace Company.1)Accelerator section design Fig.1 and Fig. 2 are the schematic diagram of coved cavity accelerating structure,the formulesof variational method are（1） to（4 ） from papor[4], if frequency = l 300MHz,mode θ= 3π/4,curvature radii R₁=4.19 1mm,R₂=6.985mm,R₃=27.940mm,nosecon-angleψ=30deg,cavityspacing D = 86,487mm and nosecone-thickness t=10.439mm are given,the main parameters ofthe accelarating section are got in Table l and 2,delineates the design parameters for a moderatelyconstant gradient acceleration section.2)Cavity structure design and measurements of the frequency characteristic of the cavities As well known that the difficuly to match the coupling cavity is the influence between thefrequency and coupling coefficient of the cavity,So a movable nosecone is designed in the couplingcavity（see Fig.3）,the length of the nosecone is 60mm,the maximum,radius of the nosecone is50mm and the movable distance of the nosecone is ± 3mm,a screw is used for fixing it.When thenosecone moves into the coupling cavity,the distributive capacitance between the nosecone andcavity wdll will be increased,than the cavity frequency will be reduced and vice velsa. From themicrowave measurement the nosecone moves 0.0 l mm,the frequency will be change 200kHz. Withthis way,the coupling coefficient β≤1.03 can be got at the frequency f=1300MHz,The 3π/4-modetravelling wave coved cavity matching is made by accuracy numerical control lathe with man-madediamond, Fig.4 is the picture of aluminium coved cavity. In order to excite the 3π/4-mode in thecavities,three and two half cavities are needed in the measurement of the frequency characteristic,Fig.5 is the block of the measurement.Table 3 and 4 are the influence of the inside cavity diameter2b a nd the nosecone length changes to the cavity frequency The design and the cold testing results of the travelling wave coved cavity is identical,so thiskind of cavity will be a fine and new accelerating structure for FEL research.更多还原