Study On The Millimeter And Submillimeter Wave Radiation Sources Driven By Two Electron Beams

Millimeter and submillimeter waves with the unique advantages in the electromagnetic spectrum are very important for the national defense military and civil applications. However, the radiation sources are one of the keys to develop the applications of millimeter and submillimeter waves. At the band of millimeter and sub-millimeter, Free-electron laser (FEL) is one of important radiation sources of high power and tunable frequency. On the other hand, the vacuum electron devices based on grating, such as the backward wave oscillator (BWO), Orotron and Smith-Purcell (SP) radiation source, are widely attentive by the researchers, for which are a promising alternate of the development of tunable, compact, powerful radiation source. In this dissertation, an approach of using two-stream intability (TSI) to improve the performances of such kinds of devices is presented. The detailed investigations on the beam-wave interactions of the two electron beams device have been performed through the theoretical analyses, particle-in-cell (PIC) simulations and experiment study. The research results show the performances of devices are markedly enhancement due to the two beam interactions. The major achievements of this dissertation are as follows:(1) The two-stream free-electron laser (FEL) with an axial guiding magnetic field (AGMF) is presented. The dispersion equation with an AGMF is derived with the help of linearized fluid theory and solved numerically. The results show that the linear growth rate of beam-wave interaction is enhanced and band width is enlarged as the presence of AGMF. Moreover, a considerable enhancement of growth rate maximum is obtained at the the optimum velocity separation and current ratio of two electron beams.(2) The two electron beams planar closed grating of Cherenkov device is studied. The dispersion equations are derived and solved, the results show the linear growth rate and band width of two electron beams device are larger than that of single beam due to the TSI. The results of PIC simulation show that the radiation power of two electron beams Cherenkov device is obtained a considerable enhancements at a suitable voltage ratio and current ratio. (3) A novel approach to the enhancement of SP radiation employed the TSI in planar open grating is presented. The planar open grating is driven by two electron beams that propagate over the grating with a velocity separation. Through the solutions and analyses of dispersion equation, the results show that the linear growth rate of the two electron beams system can be achieved a considerable improvement at the synchronization point due to the TSI. With the help of PIC simulation, the enhancement of SP radiation power, the shortened saturated time and the lessened threshold current are observed(4) The millimeter radiation source of cylindrical grating driven by two electron beams is studied. The dispersion equation of two separated beams in the cylindrical grating is derived and solved. The results show that the linear growth rate is markedly enhanced due to the TSI. The PIC simulation results show that the radiation power of two beam system is larger than that of single beam. On the other hand, the effect of distance between the two electron beams on the on the performamance is investigated. The PIC results show the TSI is weakened with the increasing of two electron beams separated distance, resulting in the sharp decrease of radiation power.(5) For the first time, the experiment of millimeter-wave-band relativistic diffraction generator (RDG) driven by two electron beams is projected and performed. Main radiation mode of the device tested by neon tube array is TM symmetry, and with the help of dispersion delay line, the measured radiation frequency is 30.27GHz. The radiation power of two beams RDG and single beam RDG are 186.69MW and 139.44MW, respectively. The experiment results show the radiaton power is enhanced and the pulse width is increased by use of two electon beams.