Study Of The Forming Technology And Application Of Large-Orbit Electron Beam

Peniotron is a cyclotron fast wave tube. Different from the electron cyclotron maser interaction used in conventional gyrotrons, the peniotron using phase separation effect to realize the net energy exchange between the electrons and the high frequency field. There are no "adverse" electrons in the entire energy exchange process and the residual energy of all the electrons are relatively the same, it’s easy to collect using the depressed collector technology, In addition, the strong magnetic field usually provided by superconducting magnet could be lowered greatly by selecting the high order gyro-harmonic mode, while relative high energy conversion efficiency still can be obtained. It’s a more conductive way for developing median power high efficiency millimeter wave and sub-millimeter wave source with permanent magnet system. As a result, many researchers pay great attention to the peniotron due to its high efficiency. It’s discovered that the beam quality has a great influence on the device performance, so it’s an important issue to explore new electron optical system to meet the peniotron’s requirements.Based on the equation of electron motion, the conservation of canonical angular momentum and the total energy, we derived the electron’s radial, angular and axial motion equation in the ideal cusp and non-ideal cusp respectively, and obtained the analytical solution. It pointed out that the key in the formation of large-orbit electron beam was the reversal magnetic field. Then, we analyzed the different kinds of large-orbit electron gun in detail, and designed the electron optical system of the third-harmonic peniotron. The main works and results are listed bellow.Firstly, on the basis of analyzing the general regularities of electron motion in the general reversal field, we derived the relationship between parameters at the cathode and parameters at the interaction area irrespective of the intermediate process, which simplifies the analysis of different program. Then we analyzed the various causes of the velocity spread and the rules of the guiding center deviation, and the corresponding velocity spread suppression method and the guiding center compensation method of the large-orbit electron beam were brought forward. The cores of the guiding center compensation method including the several parts:using the magnetic field configuration that can be realized practically; controlling the initial magnetic flux spread; and adjusting the electrons’ phase at the Cusp area.Secondly, a novel approach to get large-orbit electron beam is demonstrated using gradually-changing reversal magnetic field. On the basis of gradually-changing reversal magnetic field theory, we designed a large-orbit electron beam with low velocity spread and low guiding center deviation. Different from the traditional three-step method, our design doesn’t pursuit the formation of thin tubular electron beam and the utilization of mutation reversal magnetic field, which reduces the difficulties of structure complexity and tube-making process, In addition, the cathode emission band can be placed in the axial magnetic field before the magnetic reversal point where its magnitude decreasing gradually, by controlling the angular momentum differences between every trajectory starting points and using the offset effect of various unfavorable factors to reduce eccentricity and velocity spread. We provide two technical ways to obtain high quality large-orbit electron beam:fine-tuning the axial position of the electron gun in the magnetic field and adjusting the height of the central proection.Thirdly, the generation of axis-encircling large-orbit electron beam using magnetron type injection gun is studied theoretically and numerically. In the simulation, the magnetic field is no longer an ideal one; instead, it’s a gradually reversal magnetic field that can be realized by actually coils and magnetic shield, which increases the possibility of application, In addition, the cathode emission band is parallel no longer to the system’s axis but also to the magnetic field lines, in this way it eliminates the initial angular momentum spread at the cathode and helps to reduce the velocity spread greatly. By adjusting the voltages of the two anodes, the beam quality can be modulated easily to meet the specific requirements of different gyro-devices. Through numerical simulation by EGUN, a large-orbit electron beam with axial velocity spread of1.82%, guiding center deviation of6.1%, and velocity ratio of1.67is obtained. The scheme provides a new electron gun candidate for the large-orbit devices.Fourthly, we write the self-consistent nonlinear program for peniotron, by which the compute speed is increased greatly. The four-slotted third-harmonic peniotron is deeply studied by the small signal theory and an example peniotron is designed. Based on the requirements of the third-harmonic peniotron, we designed a large-orbit electron gun. In the gun, an electron beam with axial velocity spread of4.78%, guiding center deviation of7.18%and velocity ratio of2.2is generated, which satisfies the special requirements of beam-wave interaction in third-harmonic peniotron. Driven by this gun, the peniotron is predicted to yield an output power of31.9kW at30GHz, with the microwave conversion efficiency up to49.4%, which shows the perfect matching between the high frequency system and its electron-optical system. Finally, it is found that the device performance is very sensitive to the relative axial position between the magnetic system and the electrode system. If the magnetic system shifts to the right for0.8mm, the device efficiency would decrease from49.4%to31.7%. This phenomenon provides meaningful information in the device hot-test.Lastly, based on the reliability of current magnetic and process condition, the permanent magnet system and the large-orbit electron gun are designed. The NdFeB32is used for the permanent magnet material. The size of the total magnet is small and compact enough, and the total weight is about100kg. The amplitude of the main field is0.396T, and the length of the uniform region is as long as50mm. After optimization, an axis-encircling electron beam with axial velocity spread4.48%, guiding centre deviation ratio6.97%and high velocity ratio2.03is obtained, which satisfies the3rd-harmonic peniotron. Driven by the electron gun, an output power of35.4kW is obtained and the device efficiency is up to56.0%, this is an attractive result in laboratory platform.