.0.22 The Thz Gyrotron Gradient Output Structure

The fast wave device gyrotron is base on the radiation theory which is excitated by electrons cyclotron resonance. Its frequency is very high especially at the millimeter and sub-millimeter wave band. And it can produce high output power in pulse and continuum wave. It can be used in plasma heating, accelerator, radar, communication, electron rivalry , microwave weapon and so on .The THz radiation resource is one of the many emphases researching item in THz technique at international academe recent years. Because the THz is between the millimeter wave and the infrared, it is difficult to produce the THz radiation resonance. But the application such as the radars and far distance detecting need great power THz resource. The gyrotron is the only device who can produce great power THz wave. However, the smaller the gyrotron's size, so it become very difficult to guarante the high gyrotron output mode's purity and power. Therefore,it is especially important for high frequency THz gyrotron to have a good transmission system ,this article focuses on reducing the unwanted mode excitation, improving mode purity and transmission efficiency, and a gyrotron output taper systerm has designed of which working frequency is 0.22THz and the main mode for transmission is TE03, so that gyrotron output can reach the original design requirements.The gyrotron output taper systerm is actually a range of taper circular waveguide beteween the output cavity and the output window. The special difficulties in the design of gyrotron tapers in comparsion with highly oversized waveguide tapers for other transmission systems as follows.a. At the taper input the working mode is very close to cut-off. Input reflection as well as forward- and backward-scattered modes have to be considered.b. In the case of conventional gyrotrons,where the electron beam collector serves as an output waveguide, the ratio R2/R1 of the collector to the cavity output radius is very large so that there is strong excitation of many unwanted modes.c. Gyrotron working modes are higher-order modes which couple to higher and lower undesired mode neighbours withΔm= 0(circular symmetry). TEmp modes with m>0 couple not only to TEmq modes ,but also excite TMmq modes.In this paper ,First of all, coupled-wave equations are obtained by using standing-wave field expansion method to expan Maxwell's equations ,then the artical derived a very important parameter in the coupled-wave equations - the coupling coefficients of the expression in different situations. Secondly, based on coupled- wave equations,the push to a general taper waveguide design theory is obtained, and according to this theory and the design parameters , The contours of the five waveguide taper of rising cosine, Dolph-Chebychev waveguide graded, improved Dolph-Chebychev, Parabolic, rising Sine waveguide taper are designed. Finally, with two numerical analysis methods of coupled-wave equations numerically integrating and scattering matrix ,such five designed tapers'transmission performance are analyzed,and find that they are agree well with the results of HSSS 10.0. Then it is to be find that a modified Dolph-Chebychev waveguide taper of a 32.6432 mm length have a best transmission performance as 0.22 THz gyrotron output structure.