热电子对低频等离子体漂移波的稳定作用

本文用磁流体理论导出了热电子等离子体中,等离子体密度梯度驱动的低频漂移波的色散关系,分析了热电子的稳定作用。热电子成分稳定等离子体低频扰动的物理机制是charge uncovering效应,它只依赖于热电子同等离子体的密度比α,而不依赖于热电子的β值。热电子能降低等离子体交换模和漂移波的增长率,减少漂移波引起的等离子体反常输运损失。稳定等离子体交换模要求α≈2％,稳定等离子体漂移波要求α≈40％。理论上预示了在热电子等离子体中,等离子体漂移波是最重要的低频不稳定性。 关键词：     

简单磁镜中热电子等离子体的基本特性

本文叙述了简单磁镜中,热电子等离子体的实验结果。微波在基频共振层击穿气体产生等离子体,二次偕振加热产生热电子环。等离子体激发了低频交换模和漂移波,热电子环对等离子体的扰动有稳定作用。     

热电子等离子体无碰撞漂移波的稳定性

本文采用Vlasov方程,分析了热电子等离子体中低频交换模和漂移波的性质,讨论了热电子成分的稳定作用。稳定交换模要求热电子成分约为10％,稳定漂移波要求热电子成分约为30%。文中还讨论了离子有限Larmor半径、等离子体密度梯度和温度、磁场曲率、扰动波长等参数对稳定性的影响。同MHD近似下强碰撞漂移波的结果相比较,热电子对无碰撞漂移波有更好的稳定作用。 关键词：     

热电子等离子体低频不稳定性的非线性理论

本文分析了热电子等离子体中低频漂移不稳定性和交换不稳定性的非线性性质,导出了扰动幅度随时间变化的非线性耦合方程,得到了等离子体密度扰动的饱和幅度,讨论了热电子成分对饱和幅度的影响。漂移波引起的等离子体密度扰动相对幅度约20％,交换模引起的等离子体密度相对扰动幅度约5％。当热电子成分达到线性稳定条件所要求的阈值时,漂移波和交换模的饱和幅度降为零。 关键词：     

磁镜等离子体中电子回旋波加热实验的理论研究

本文利用平行平板模型,给出了在不同位置、以不同角度入射到平衡的磁镜等离子体中电子回旋波的传播轨迹;利用线性理论计算了O,X波能量分别被本底电子、热电子吸收的波能量沉积率。根据计算结果,文中对加热本底等离子体的特征进行了描述,对非封闭热电子环的形成作了初步解释。     

热电子等离子体的低频交换不稳定性

本文用磁流体理论,导出了包含导电端板“线结”效应的热电子等离子体低频交换模的色散关系,分析了热电子环的稳定作用,求出了稳定性判据。“线结”效应能大大降低交换模的增长率。取热电子密度为零,就得到简单流体等离子体的结果。     

共振吸收引起的冷等离子体波碎

本文采用渐近方法求解了不均匀冷等离子体的修正电容器模型方程(非线性)。Dawson仅给出了一个波碎条件,但应用于不均匀等离子体时是不完备的。本文补充了使其完备化的第二个波碎条件,并同时、唯一地确定了波碎位置与波碎时间,进而导出了热电子最大能量与局部电场振幅的计算公式。新公式的预言,尤其是波碎时间和热电子最大能量与实验符合很好。 关键词：     

等离子体模型碰撞项的比较

本文在两种碰撞模型(BGK模型和LB模型)下,计算了碰撞对等离子体色散方程的影响。碰撞的主要作用是使色散函数Z(ξ)变为广义色散函数W(ξ,ν)。分析比较了两种模型下广义色散函数的性质。讨论了碰撞对低频漂移波(局域模)和离声波稳定性的影响。分析表明,LB模型不仅在物理上更为合理,而且在计算及表达形式上也比BGK模型更为简明。 关键词：     

高能α粒子对环形等离子体中低频漂移波稳定性的影响

本文利用强耦合近似,研究了高能α粒子密度梯度对环形等离子体中低频漂移波稳定性的影响。结果表明:对频率与离子反磁漂移频率ω_1相近的漂移波,α离子有降低稳定性的作用;对频率远比ω_i高的弱剪切中的漂移波,α粒子起稳定作用。     

“重力”效应对漂移波稳定性的影响

本文在直柱位形中,用强耦合近似方法分析了“重力” 场随极向角及环向角的变化对剪切磁场中漂移波稳定性的影响。我们发现,即使环向场波纹度很小,但由于其随环向角变化频率较高,对漂移波稳定性的影响不容忽略。特别是,当只考虑极向模耦合时稳定的漂移波,同时考虑环向场波纹度引起的环向模耦合时,变为不稳定。     

Thermal annealing and light irradiation effects on hole and electron drift mobilities of Se93.5As6.5 and Se94.3Ge5.7 films

Thermal annealing and light irradiation effects on hole and electron drift mobilities were studied for amorphous Se_93.5As_6.5 and Se_94.3Ge_5.7 films by means of a time-of-flight technique. The electron drift mobility and its activation energy show a drastic increase after the heat and light treatments, while the hole drift mobility remains almost unchanged. The change of electron transport is attributed to a relaxation of local structural distortion, which is correlated with relatively shallow localized states. The present experimental results are inconsistent with the prior proposal that electron transport in amorphous selenides is correlated with Se₈ ring molecules.     

THE PRODUCTION AND CHARACTERISTICS OF THE SLOSHING ELECTRONS IN A MAGNETIC MIRROR

The experiment on the formation of sloshing electrons by electron cyclotron resonance heating in a magnetic mirror is described, and the physical properties of them are investigated. The results show that (1) the sloshing electron configuration is formed, and its characteristics are very different from those of the hot electron ring; (2) R_n, the hot electron density ratio which represents the sloshing electron configuration, decreases as the mirror magnetic field increases, and the maximum of R_n can reach about 2.65.     

Diffusion theory of the positive column with two-stage ionization and collisional deexcitation

The diffusion theory of the low pressure positive column is extended to account for collisional deexcitation as well as for two-stage ionization by electron impact. This extension results in the equationn″(ξ)+n′(ξ)/ξ+n(ξ)+vn ²(ξ)[1+μn(ξ)]^-1=0, which is solved numerically for the value ofξ ₁ which satisfies the boundary conditionn(ξ ₁)=0 for different values of the parametersν andμ.     

热电子、双离子成分对离子漂移迴旋不稳定性的影响

分析了热电子、温(热)离子成分对离子漂移迴旋不稳定性的影响。给出了临界稳定热电子成分值α与温(热)离子成分值、离子温度比和离子抗磁漂移速度的关系;讨论了热电子、温(热),冷离子成分对不稳定性各谐频分支的影响;分析了热电子成分稳定作用的物理机制。     

High field transport properties in a GaN/AlGaN heterostructure

The drift velocity, electron temperature, electron energy and momentum loss rates of a two-dimensional electron gas are calculated in a GaN/AlGaN heterojunction (HJ) at high electric fields employing the energy and momentum balance technique, assuming the drifted Fermi–Dirac (F–D) distribution function for electrons. Besides the conventional scattering mechanisms, roughness induced new scattering mechanisms such as misfit piezoelectric and misfit deformation potential scatterings are considered in momentum relaxation. Energy loss rates due to acoustic phonons and polar optical phonon scattering with hot phonon effect are considered. The calculated drift velocity, electron temperature and energy loss rate are compared with the experimental data and a good agreement is obtained. The hot phonon effect is found to reduce the drift velocity, energy and momentum loss rates, whereas it enhances the electron temperature. Also the effect of using drifted F–D distribution, due to high carrier density in GaN/AlGaN HJs, contrary to the drifted Maxwellian distribution function used in the earlier calculations, is brought out.     

Understanding the effect of inhomogeneous fuel–air mixing on knocking characteristics of various ethanol reference fuels with RON 100 using rapid compression machine

We investigated the effect of inhomogeneous mixing of a fuel–air mixture in a spark-ignition engine on knocking characteristics and the dependency of the effect on the fuel, especially for various ethanol reference fuels with a fixed RON of 100. We assumed that a locally lean spot and rich spots exist in the end gas owing to inhomogeneous mixing and calculated their thermodynamic states with a multizone spark-ignition engine simulation. Subsequently, the ignition delay around the state was measured using a rapid compression machine at varying temperatures and equivalence ratios. The obtained results were processed to calculate ξ, which is the ratio of sound speed to auto-ignition propagation speed, and $?$, defined as the time required for acoustic front to exit the hot spot divided by the excitation time. Then, we analyzed the knocking occurrence and intensity from the locally lean spot and rich spots based on Zel'dovich and Bradley's ξ–$?$ theory. Our results show that the lean spot has a shorter ignition delay than the stoichiometric mixture (ξ?>?0) regardless of the ethanol content, whereas the rich spot does not (ξ?<?0), implying that only the lean spot can initiate knocking. This is because the temperature of the lean spot is higher than the surrounding mixture owing to its higher specific heat ratio and less charge cooling effect. In addition, the knocking intensity from the lean spot is found to be maximized with ERF0, showing the largest ${\xi }^{?2}$ value. Further analysis was conducted by dividing ξ into the effect of the temperature gradient, ξ_T, and that of the equivalence ratio gradient, ξ_?. Consequently, we found that the magnitude of ξ_T is related to the activation energy of the fuel, while that of ξ_? is determined by the dependency of the pre-heat release characteristics of the fuel on the equivalence ratio.     

电子迥旋加热等离子体及热电子环特性的实验研究

在简单磁镜MM-2中,采用15GHZ大功率迴旋管进行了电子迴旋共振加热(ECRH)实验。结果表明,随充气压强的提高,预电离时间迅速变短。在高气压“C-模式”运行区,等离子体径向密度分布呈马鞍形。在迴旋管输出30kW功率的条件下,适于建立热电子环的气体压力窗为(0.4—1.2)×10^-5Torr。利用一个可移动Laugmuir探针配合反磁测量的简便方法,在中心场为2.95kG时,确定了电子环半径为7cm,环厚约4cm,环的轴向边界由z=±10cm一直延伸到z=±20cm。热电子温度为140—170keV,热电环平均β值为(4—5)％。观测到了由热电子环不稳定性引起的迸发式径向电子逃逸,并同时发生反磁信号跌落。