A Study of Ionization Front Velocity in dc Pulsed Plasmas

The ionization front velocity in a de cylindrical plasma is reported. This parameter has been determined as the ratio between the distance separation of two Langmuir probes, Δz, and the time Δt which is needed for the ionization front to cover the distance Δz. A theoretical model which allows to obtain the functional relationship of ionization front velocity with the stationary electron density has been developed. A good agreement, both qualitatively and quantitatively, has been obtained.     

同轴回旋行波放大器的理论和数值研究

 给出了一组描述同轴回旋行波放大器中波束相互作用的非线性自洽方程组，对该放大器的运行特性进行了研究。得到：在小信号区，辐射场的增益随同轴波导的内外半径比b/a的增加而增加，达到饱和时的辐射功率仅略有下降；内外导体管壁上的功率损耗密度随b/a的增加而减小。采用电压为90kV，电流为10A，纵向速度零散度为3%，速率比为1的电子束，在34.26～36.78GHz的频率范围内，计算得到了峰值功率约230kW的微波输出，相应的增益和效率分别为46.6dB和25.5%，带宽为7%，内外导体管壁上功率的最大损耗分别为80和56W/cm²。     

大回旋半径电子枪渐变线圈磁场的设计及优化

对大回旋半径电子枪的渐变线圈磁场进行了设计,采用3个线圈实现所需要的渐变磁场分布,增加了线圈磁场系统的调节能力,理论和计算机仿真的磁场分布结果符合得很好。将实现的渐变磁场分布同给定的静电场分布相结合,通过求解带电粒子的运动方程得到了粒子轨迹,在此基础上建立大回旋半径电子枪的3维粒子仿真模型,在给定静电场分布条件下分析了3个线圈安匝数对电子束参数的影响,完成了工作电压为40 kV、工作电流为1 A的大回旋半径电子枪的参数优化,得到了横纵速度比为1.4～2.5,纵向速度离散小于8%(横纵速度比为1.9时)的大回旋半径电子束。     

二次谐波回旋行波管Cusp电子枪的模拟与实验研究

 利用3D PIC软件和乌克兰开发的电子光学计算软件TAU对二次谐波回旋行波管Cusp电子枪进行模拟，提取电子的3维运动速度计算横纵速度比。在阳极电压和阴极电流变化的条件下，对电子速度比和速度零散随之而变化的情况进行了模拟，得到平均速度比1.1和平均速度零散9.5%的结果。基于电子平均半径，并根据电子平均半径与横向速度、纵向速度的关系提出了一种实验测量速度比的方法。当电子轰击荧光屏玻璃时，玻璃上的荧光物质感应到光斑，测量空心光斑的平均半径可计算得到电子速度比，其结果与模拟值误差15%。     

低速度零散会切电子枪的设计和数值仿真

根据拉格朗日方程对电子在平滑会切磁场中的径向波动与速度零散的关系进行讨论。运用Matlab,Magic软件相互结合的方法设计电子枪结构和磁场。用Matlab程序模拟单电子在给定电场、磁场中的运动,分析了单电子径向速度对零散的影响,并优化磁场分布。设计的磁场可以有效地减小单电子束径向速度,降低电子束速度零散。用Magic软件对电流为1 A、能量为30 keV的电子束在优化磁场中的运动进行仿真,得到的电子束速度比约为2,速度零散小于2.5%,轴向速度零散小于8.5%。     

1THz回旋管双阳极磁控注入电子枪的分析及设计

基于电子光学理论,通过编程进行大量的数值计算,设计了一支用于1THz回旋管的双阳极磁控注入式电子枪.对双阳极磁控注入电子枪的计算及设计进行了阐述,并对1 THz回旋管电子枪中高磁压缩比(f_m=125)可能导致电子反转的问题进行了详细的分析和模拟.通过对电子枪进行了仿真和优化,最后计算和设计了一支速度比适中(α=1.3),速度零散较小(Δβ<8%) 的电子枪.     

170 GHz回旋管大束流双阳极磁控注入电子枪的分析及设计

 基于绝热压缩原理和强流电子光学理论,设计了一只170 GHz回旋管双阳极磁控注入电子枪,经过理论分析及计算,采用仿真软件进行模拟和优化,最终得到的电子枪的电子注速度比为1.31,横向速度零散度为3.5%,纵向速度零散度为6.1%,束电流为51 A。讨论了阴极磁场、控制阳极电压和第二阳极电压等因素对电子注性能的影响,发现电子注的速度比和速度零散度对这些影响因子的变化都非常敏感:随着阴极磁场的增大,电子注的速度比减小,纵向速度零散度先增大后减小,横向速度零散度先减小后增大;阳极角越接近阴极倾角,纵向速度零散度越小;阳极角向着减小阴阳极间距的方向变化时横向速度零散度变小;增大第一阳极电压可以增大电子注的速度比和电子注的速度零散度。在两阳极电压不变的情况下,增大阴阳极之间的距离会使电子注的速度零散度和电子注的速度比减小。     

Cq+(q=1-4)与He,Ne,Ar碰撞的电子损失截面测量与研究

在中能区测量了C^q+(q=1-4)与He,Ne,Ar气体原子碰撞的电子损失截面,计算分析了入射离子损失两个电子与一个电子的总截面比 R₂₁. 单反应道分析无法完全解释所有实验结果,必须同时考虑入射离子的电子损失、电子俘获和靶原子电离各种出射道间的耦合作用. 对于不同靶原子的碰撞,入射离子损失一个电子和两个电子的速度阈值可以由屏蔽和反屏蔽理论解释. 然而,该理论不能完全解释截面比 R₂₁ 关键词： 离子-原子碰撞 截面 电子损失     

Cross sections of Oq+（q=1-4） electron loss in collisions with He,Ne and Ar

Electron-loss cross sections of O q+(q = 1 4) colliding with He,Ne and Ar atoms are measured in the intermediate velocity regime.The ratios of the cross sections of two-electron loss to that of one-electron loss R 21 are presented.It is shown that single-channel analysis is not sufficient to explain the results,but that projectile electron loss,electron capture by the projectile and target ionization must be considered together to interpret the experimental data.The screening and antiscreening effects can account for the threshold velocity results,but cannot explain the dependence of the ratio R 21 on velocity quantitatively.In general,the effective charge of the target atom increases with velocity increasing because the high-speed projectile ion can penetrate into the inner electronic shell of target atom.Ne and Ar atoms have similar effective charges in this velocity regime,but He atoms have smaller ones at the same velocities due to its smaller nuclear charge.     

Dielectric-loaded wideband gyro-TWT

The bandwidth of a gyro-TWT (traveling-wave tube) can be widened by employing a dielectric-loaded waveguide to reduce the circuit's dispersion. Fast wave interaction allows the requirements on the beam's quality to be relaxed compared with slow wave interaction. A low-α (≡ν_⊥/ν_z) electron beam is chosen to avoid the absolute instability and minimize the possibility of dielectric charging. This device is investigated using a self-consistent single-mode, large-signal simulation based on a slow time scale formulation. Simulation results show that a constant drive bandwidth of 20% can be achieved for a 100 kV, 5 A electron beam with a velocity ratio of α=0.59 and an axial velocity spread of 2.0%. The growth rate is relatively low because of the low α of the electron beam. The design of a proof-of-principle experiment is described. The tube is expected to deliver a power of 80 kW from 9 to 11 GHz with 15% efficiency and a saturated gain of 30 dB. The performance of a single-anode magnetron injection gun designed to produce the required high-quality electron beam has been studied through simulation     

大回旋电子束双磁会切电子枪的设计

 分析了Ka波段二次谐波回旋行波管双磁会切电子枪的理论模型，计算了电子枪的设计参数；采用EGUN软件进行模拟，设计出了产生大回旋电子束的双磁会切电子枪。该枪电压为70 kV，电流为3.35 A，电子束横纵速度比为1.62，速度零散为4.2%。给出了电子束速度比、速度零散沿轴线的分布，进而讨论了阳极电压对电子束性能的影响，结果表明选择适当的阳极电压和阴极磁场对得到好的电子束参量作用明显。     

Inverse Bremsstrahlung absorption coefficient in inhomogeneous plasma with nonextensive electron velocity distribution and Tsallis exponential electron density profile

Inverse bremsstrahlung (collisional) absorption of the laser beam is studied in plasma with a generalized (q-nonextensive) electron velocity distribution and some kind of generalized electron density profile. It is shown that for some values of parameters designating the q-nonextensive electron velocity distribution function and its generalized density profile, the calculated absorption coefficient reduces to the already known cases with Maxwellian velocity distribution with linear and exponential density profiles.     

LARGE-SIGNAL SIMULATIONS OF A GYROTRON TRAVELING-WAVE AMPLIFIER WITH A MODE-SELECTIVE INTERACTION CIRCUIT

A self-consistent nonlinear theory is used to analyze the saturated performances of a Ka-band gyrotron traveling wave amplifier (gyro-TWA) operating at the fundamental with a mode-selective interaction circuit involving a tapered vane-slot mode converter. The amplifier is predicted to generate 140 kW saturated output power with 33.3% efficiency, a saturated gain of 33dB, and a 3dB bandwidth of 2.7 GHz (8%) for a 70 kV, 6A electron beam with a velocity ratio of 1.0 and an axial velocity spread of 5%.     

Effect of non‐extensivity parameter q on the damping rate of dust ion acoustic waves in non‐extensive dusty plasma

Kinetic theory has been applied to study the damping characteristics of dust ion acoustic waves (DIAWs) in a dusty plasma comprising q‐non‐extensive distributed electrons and ions, while the dust particles are considered extensive following the Maxwellian velocity distribution function. It is found that the results of the three‐dimensional velocity distribution function are more accurate compared to the results of the one‐dimensional velocity distribution function. The numerical solution of the dispersion relation is carried out to study the effect of the non‐extensivity parameter q on the dispersion, the damping rate, and the range of the values of the normalized wavenumber ( k λ_D) for which the DIAWs are weakly damped. It is found that the change in the value of the electron non‐extensivity parameter q_e has a minor effect on the dispersion, the damping rate, and the range of the values of the normalized wavenumber ( k λ_D) for which the DIAWs are weakly damped, while on the other hand, ion non‐extensivity parameter q_i has a strong effect on these arguments. The effect of other parameters, such as the ratio of electron to ion number density and ratio of electron to ion temperature, on the damping characteristics of DIAWs is also highlighted.     

Influence of conduction heat loss on enhancing the heat transfer performance of a square flat plate with constant heat flux by an impinging jet in cross-flows

An experimental setup was built to study the influence of conduction heat loss on the convective heat transfer performance enhanced by an impinging jet in cross-flows. Results revealed that the conduction heat loss ratio (E_c/E) is between 12.0% and 40.1%, and it decreases nonlinearly with the ratio of jet-to-cross-flow velocity. The relative Nusselt number increases with the ratio of jet-to-cross-flow velocity. The maximum peak value and the average are 8.1 and 6.4, respectively. The distribution of the relative Nusselt number seems to be flattened by assuming a constant conduction heat loss ratio.     

双阳极回旋管磁控注入电子枪设计

对真实磁场进行拟合,根据电子光学原理以及绝热压缩理论,运用EGUN软件,设计了工作模式为TE34,19的170 GHz回旋管双阳极磁控注入电子枪。最终得到的电子注速度比约为1.3,速度零散小于3%。分析了调节磁场位置、阴阳极间距、阳极间距等因素对电子注性能的影响。结果表明:电子注的速度比和速度零散对于这些影响因子的变化比较敏感,随着阴阳极间距以及阳极间距的增加,速度比逐渐减小,速度零散先减小后增大。设计的双阳极电子枪已应用于整管实验中。     

0.6 THz三次谐波大回旋电子枪设计

基于会切磁场的理论模型,采用粒子模拟软件对0.6 THz三次谐波的太赫兹回旋管所需的大回旋电子光学系统进行研究。通过大量的模拟计算,分析讨论了不同参数对电子注的横向速度离散、纵向速度离散及横纵速度比的影响,优化了电子光学系统的性能参量,得到符合设计要求且具有工程实际应用的电子枪,该电子枪能够产生55 kV,1 A,横向速度离散为3.39%、纵向速度离散为7.10%、横纵速度比为1.53的大回旋电子注。     

Fluid Model of a Sheath Formed in Front of an Electron Emitting Electrode Immersed in a Plasma with Two Electron Temperatures

The formation of a sheath in front of a negatively biased electrode (collector) that emits electrons is studied by a one‐dimensional fluid model. Electron and ion emission coefficients are introduced in the model. It is assumed that the electrode is immersed in a plasma that contains energetic electrons. The electron velocity distribution function is assumed to be a sum of two Maxwellian distributions with two different temperatures, while the ions and the emitted electrons are assumed to be monoenergetic. The condition for zero electric field at the collector is derived. Using this equation the dependence of electron and ion critical emission coefficients on various parameters ‐ like the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons ‐ is calculated for a floating collector. A modification of the Bohm criterion due to the presence of hot and emitted electrons is also given. The transition between space charge limited and temperature limited electron emission for a current‐carrying collector is also analyzed. The critical potential, where this transition occurs, is calculated as a function of several parameters like the Richardson emission current, the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Single electron capture in collisions of N^q＋ （q = 5, 6, 7） ions with helium

Close-coupling calculations are carried out for cross sections of the single electron capture in collisions of N^q+ (q = 5, 6, 7) ions with helium atoms in the collision velocity range from 0.3 a.u. to 1.8 a.u. The relative importances of the single ionization (SI) to the single capture (SC) are investigated for the N^q+ (q = 5, 6, 7) projectiles, respectively. The SI/SC cross section ratio for the N⁷⁺ projectile obtained from our calculations is in excellent agreement with the experimental data. The ratio curves also show us distinct behaviours when the charge of the projectile is different. The partial electron capture cross sections for different projectiles indicate that the electron on the target He atom tends to be captured by the projectile into its lower orbital of the outer shell with the decreasing projectile charge.     

8 mm三次谐波潘尼管大回旋电子枪设计

根据现有磁体条件和工艺设计了一过渡区较长的倒向磁场系统,其主磁场为0.396 T,反向磁场为-0.033 T,并给出了一种实用8 mm三次谐波潘尼管电子枪的设计结果。该大回旋电子枪工作在43.5 kV,1.45 A下,阴极可置于轴向磁场幅值渐减区域。该结构电子枪不追求在通过反转点之前形成薄的环形电子束,不利用突变倒向磁场,不需要刻意控制磁力线与电子注包络走向的一致性,显著降低了调试的难度和要求。最终优化所得电子注的纵向速度零散为4.78%,偏心率为7.18%,速度比高达2.2,而速度比的零散仅为4.88%,满足三次谐波潘尼管的要求。经大信号模拟计算,在该电子枪驱动下,潘尼管器件功率可达31.9 kW,效率高达49.4%,总体参量仍具有吸引力且建立在可实现的电子光学系统基础上。