The generalized dispersion equation for longitudinal oscillation in an unmagnetized, collisionless, isotropic and relativistic plasma is derived in the context of nonextensive q-distribution. An analytical expression ...The generalized dispersion equation for longitudinal oscillation in an unmagnetized, collisionless, isotropic and relativistic plasma is derived in the context of nonextensive q-distribution. An analytical expression for the Landau damping is obtained in an ultra-relativistic regime, which is related to q-parameter. In the limit q →1, the result based on the relativistic Maxwellian distribution is recovered. It is shown that the interactions between the wave and particles are stronger and the waves are more strongly damped for lower values of q-parameter. The results are explained by the increased number of superthermal particles or low velocity particles contained in the plasma with the nonextensive distribution.展开更多
As a novel vircator device, the coaxial vircator can attain much higher efficiency than the common virtual cathode oscillator. In this paper, coaxial vircators in three specific configurations are studied to describe ...As a novel vircator device, the coaxial vircator can attain much higher efficiency than the common virtual cathode oscillator. In this paper, coaxial vircators in three specific configurations are studied to describe the efficiency and frequency characteristics and their dependence on geometric parameters. The PIC (Particle in Cell) simulation results show that a power efficiency over 11% can be obtained from the coaxial vircator with a finite inner anode conductor, and a narrow-band output can be achieved. A direct-coupled coaxial vircator has a slightly lower efficiency of about 8%, but in this configuration the efficiency is not strongly dependent on the geometry parameters. The introduction of a reflecting cavity can effectively improve the efficiency under certain parameters. Meanwhile, the research results also indicate that improper cavity parameters will countervail some inherent advantages of the configuration with a finite inner conductor, leading to lower efficiency than that of the direct-coupled one. Meanwhile, an experiment was also carried out to testify the simulation results, and a power efficiency over 3% was obtained from the direct-coupled coaxial vircator.展开更多
In this paper, a ferroelectric polyvinylidene fluoride (PVDF)-coated porous polymer fiber based surface plasmon resonance (SPR)-like gas sensor is proposed theoretically in the terahertz (THz) region based on the tota...In this paper, a ferroelectric polyvinylidene fluoride (PVDF)-coated porous polymer fiber based surface plasmon resonance (SPR)-like gas sensor is proposed theoretically in the terahertz (THz) region based on the total internal reflection (TIR). In such a sensor, the phase matching is achieved by changing the fiber parameters and the plasmon-like phenomenon at the interface between the ferroelectric polyvinylidene fluoride (PVDF) layer and the gaseous analyte is discussed. Using a fullvector finite-element method, the core-mode loss of the fiber is calculated to measure the resolution of the sensor. The amplitude resolution is demonstrated to be as low as 1.45 × 10-4 RIU, and the spectral resolution is 1.30 × 10-4 RIU in THz region, where RIU means the refractive index unit.展开更多
Steady-state plasma generated by electron cyclotron resonance （ECR） wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge pattern...Steady-state plasma generated by electron cyclotron resonance （ECR） wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge patterns taken by the camera and the plasma parameters measured by the probes were very sensitive to the working gas pressure and the magnetic configuration of the torus both without and with vertical fields. There existed fast vertical motion of the plasma. Tentative discussion is presented about the observed phenomena such as the bright resonance layer at a high gas pressure and the wave absorption mechanism at a low pressure. Further explanations should be found.展开更多
An axially extracted virtual cathode oscillator (vircator) with a feedback annulus is proposed and configured through particle-in-cell (PIC) simulation in Ref. [1]. In this paper, the effects of the feedback mechanism...An axially extracted virtual cathode oscillator (vircator) with a feedback annulus is proposed and configured through particle-in-cell (PIC) simulation in Ref. [1]. In this paper, the effects of the feedback mechanism are studied through PIC method. The simulated results indicate that the improved new vircator can increase the output power twice large than that of the axially-extracted conventional vircator under the same condition. On the other hand, it can narrow the bandwidth and purify the modes.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 10963002)the International S & T Cooperation Program of China and Jiangxi Province (Grant No. 2009DFA02320)+1 种基金the Program for Innovative Research Team of Nanchang Universitythe National Basic Research Program of China (Grant No. 2010CB635112)
文摘The generalized dispersion equation for longitudinal oscillation in an unmagnetized, collisionless, isotropic and relativistic plasma is derived in the context of nonextensive q-distribution. An analytical expression for the Landau damping is obtained in an ultra-relativistic regime, which is related to q-parameter. In the limit q →1, the result based on the relativistic Maxwellian distribution is recovered. It is shown that the interactions between the wave and particles are stronger and the waves are more strongly damped for lower values of q-parameter. The results are explained by the increased number of superthermal particles or low velocity particles contained in the plasma with the nonextensive distribution.
基金The project supported by the National 863 Project of China (No. 2002AA834060)
文摘As a novel vircator device, the coaxial vircator can attain much higher efficiency than the common virtual cathode oscillator. In this paper, coaxial vircators in three specific configurations are studied to describe the efficiency and frequency characteristics and their dependence on geometric parameters. The PIC (Particle in Cell) simulation results show that a power efficiency over 11% can be obtained from the coaxial vircator with a finite inner anode conductor, and a narrow-band output can be achieved. A direct-coupled coaxial vircator has a slightly lower efficiency of about 8%, but in this configuration the efficiency is not strongly dependent on the geometry parameters. The introduction of a reflecting cavity can effectively improve the efficiency under certain parameters. Meanwhile, the research results also indicate that improper cavity parameters will countervail some inherent advantages of the configuration with a finite inner conductor, leading to lower efficiency than that of the direct-coupled one. Meanwhile, an experiment was also carried out to testify the simulation results, and a power efficiency over 3% was obtained from the direct-coupled coaxial vircator.
基金supported by the Major State Basic Research Development Program of China (Nos.2010CB327801 and 2007CB310403)
文摘In this paper, a ferroelectric polyvinylidene fluoride (PVDF)-coated porous polymer fiber based surface plasmon resonance (SPR)-like gas sensor is proposed theoretically in the terahertz (THz) region based on the total internal reflection (TIR). In such a sensor, the phase matching is achieved by changing the fiber parameters and the plasmon-like phenomenon at the interface between the ferroelectric polyvinylidene fluoride (PVDF) layer and the gaseous analyte is discussed. Using a fullvector finite-element method, the core-mode loss of the fiber is calculated to measure the resolution of the sensor. The amplitude resolution is demonstrated to be as low as 1.45 × 10-4 RIU, and the spectral resolution is 1.30 × 10-4 RIU in THz region, where RIU means the refractive index unit.
基金supported by USTC Research Funds of the Double First-Class Initiative (YD2140002003)Strategic Priority Research Program of CAS (XDA25010200)+1 种基金CAS Project for Young Scientists in Basic Research (YSBR060)Newton International Fellows Alumni follow-on funding。
基金the National Science Foundation of China (Nos.10235010,10335060)Funds from the Ministry of Educationthe Academy of Science of China
文摘Steady-state plasma generated by electron cyclotron resonance （ECR） wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge patterns taken by the camera and the plasma parameters measured by the probes were very sensitive to the working gas pressure and the magnetic configuration of the torus both without and with vertical fields. There existed fast vertical motion of the plasma. Tentative discussion is presented about the observed phenomena such as the bright resonance layer at a high gas pressure and the wave absorption mechanism at a low pressure. Further explanations should be found.
基金The project supported by the National 863 Project of China (No. 2002AA834020)
文摘An axially extracted virtual cathode oscillator (vircator) with a feedback annulus is proposed and configured through particle-in-cell (PIC) simulation in Ref. [1]. In this paper, the effects of the feedback mechanism are studied through PIC method. The simulated results indicate that the improved new vircator can increase the output power twice large than that of the axially-extracted conventional vircator under the same condition. On the other hand, it can narrow the bandwidth and purify the modes.
