电子回旋共振离子推力器放电室等离子体数值模拟

电子回旋共振离子推力器属于静电型推力器,具有寿命长、比冲高、结构简单、可靠性高等优点,适用于深空探测等长时间空间飞行任务.放电室是一个关键部件,其内部通过电子回旋共振产生等离子体.针对放电室内等离子体流场建立飘移-扩散近似模型,采用迎风格式有限差分法对该模型进行数值求解,得到了放电室内不同时刻的等离子体流场分布及其演化规律.数值模拟结果可以为推力器的设计和实验研究提供有用信息.     

Electron acceleration during the breaking of an intense plasma wave in an inhomogeneous plasma

We investigate the dynamics of the electron acceleration when an intense plasma wave breaks near resonance at the plasma frequency (focus) in an inhomogeneous magnetized plasma. The breaking threshold has been determined. We compare our experimental dependences of the current and energy of fast electrons on the intensity of the incident wave at various times with theoretical estimates. We show that when the breaking threshold is significantly exceeded, up to 50% of the electrons at plasma resonance are captured and accelerated by the wave.     

Measurements of plasma parameters in capacitively coupled radio frequency plasma from discharge characteristics: Correlation with optical emission spectroscopy

Plasma parameters from the discharge characteristics of a 13.56 MHz capacitively coupled radio frequency Ar plasma are evaluated on the basis of homogeneous discharge model for wide range of operating pressure. The homogeneous discharge model of capacitively coupled radio frequency discharge is modified to take into account the nonlinear plasma series resonance effect. The effect of drift velocity of the electron due to change in radio frequency electric field and operating pressure is also considered. Considerable dependent of plasma parameters on the drift velocity of the electron as well as on the plasma series resonance effect are observed in low pressure. An irregular variation of calculated plasma density with operating pressure is observed, which is reconfirmed with optical emission spectroscopy.     

Estimates of the electron density in an ECR source of calcium plasma

A technique is proposed for estimating parameters of the plasma produced by a source based on the electron cyclotron resonance. The analysis is made for the ion cyclotron resonance (ICR) facility designed for separating calcium isotopes. It is assumed that the resonance condition for an extraordinary wave is fulfilled for electrons moving towards the wave. The plasma optical thickness, the transverse energy of resonance electrons, and its dependence on the longitudinal velocity are determined. The charged particle density in the plasma flow is estimated in terms of the balance of the electrons generated as a result of vapor ionization in the discharge zone and the electron losses due to longitudinal ambipolar diffusion.     

The plasma characteristics and film formation generated by theelectron cyclotron resonance mechanism

Silicon nitride thin film (SiN_x) is deposited onto the 3 inch silicon wafer using an electron cyclotron resonance (ECR) plasma apparatus. The plasma parameters from N₂-SiH₄ electron cyclotron resonance plasma are obtained. Radial distribution of radical atom density is determined by optical emission spectroscopy. From the comparison of the uniformities of deposited film thickness, electron density and radical atom density, it was concluded that the uniformity of film thickness is related to that of radical density rather than plasma density. The dependence of the uniformity film thickness on the waveguide mode was also examined     

Attenuation properties of EM wave by magnetized nonuniform plasma slab coated on perfect conductor plane

The total amplitude reflection coefficient of EM wave in a nonuniform plasma slab coated on perfect conductor plane is newly derived by using the scattering matrix method (SMM), and the attenuation is calculated. Three types of plasma electron density profile, that is the hyperbolic, sinusoidal, and linear profiles, are used. The external magnetic field and plasma parameters such as the maximum electron density and collision frequencies are discussed to calculate the attenuation of EM wave. The calculation results show that the plasma electron density profile and maximum electron density exert a large effect to the attenuation of EM wave and the attenuation under the uniform external magnetic field is taken place by the electron cyclotron resonance absorption, the up hybrid resonance absorption and geometric resonances absorption.     

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University

Optical emission spectroscopy(OES), as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance(PMECR) ion source at Peking University(PKU). A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance(ECR) ion source [Patent Number: ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.     

The plasma oscillations spectrum of a periodically inhomogeneous 2D electron system near the perforation threshold

The transformation of the spectrum of plasma oscillations with the zero reduced wave vector in the spatially modulated two-dimensional electron system moving to the regime of isolated quasi-one-dimensional electron channels is theoretically investigated. The results provide an explanation of the well-known experimental observations of the plasma resonance transformation when a two-dimensional electron system crosses the continuity violation threshold.     

Complex impedance of nonisotermic plasma capacitor

The capacitance of a planar capacitor filled with nonisothermic collisional plasma was calculated in the hydrodynamic approximation. Resonant properties of the complex impedance of the capacitor were studied. It was shown that resonant absorption in the capacitor is caused by excitation of ion-acoustic oscillations, the excitation of electron Langmuir waves, and the geometric plasma resonance phenomenon in the low-, high-, and intermediate frequency regions, respectively.     

等离子体中电波传播的三波非线性效应

利用等离子体非线性效应的三波法是解决黑障问题的一种可能的解决方案。从三波非线性理论出发,详细介绍了转化效率的计算方法,进而对不同等离子体电子密度模型下的非线性效应进行分析。数值仿真结果表明:存在一个最优的信号入射角度,当信号以该角度入射时转化效率最大;等离子体厚度会对最佳入射角产生一定影响,当厚度减小时,最佳入射角变大;等离子体电子密度变化范围、厚度、入射波及泵源参数都相同时,共振点处电子密度导数值越大,非线性效应越强。     

Dynamics of ionization processes during the interaction of a microwave pulse with plasma near hybrid resonance

We experimentally investigated the dynamics of ionization processes and the formation of a plasma wave channel during the interaction of intense microwave pulses with a magnetized inhomogeneous plasma in the presence of hybrid resonance. The competition between fast electron and slow ionization plasma nonlinearities was studied under conditions when the electron oscillation energy in the wave field was much higher than the atomic ionization energy of the working gas.     

Nonlinear longitudinal oscillations of relativistic plasma

The investigation has been made of nonlinear forced longitudinal oscillations of a relativistic plasma. It was demonstrated that: a) the nonlinear terms (v▽)p arising in the equations of motion do not restrict the electron oscillation amplitude increase in the region of plasma resonance; b) the nonlinear terms due to the relativistic nature of oscillations, firstly, limit the oscillation amplitude in the resonance region and, secondly, lead to the development of a parametric instability. The harmonic, sub- and ultraharmonic oscillations turned out to be unstable. The conditions for the instability as well as expressions for the growth rates of unstable oscillations were obtained.     

Magneto-optical activity of Ag at the plasma frequency

Kerr activity is observed in pure Ag films in the vicinity of the plasma resonance (3.85 eV) when subjected to a strong external magnetic field. This inherent magneto-optical behaviour of Ag in a narrow wavelength range (0.12 eV) around the plasma resonance is explained utilizing the classical Lorentz-Drude model for the off-diagonal elements of the dielectric function. This activity is a consequence of a combined effect of the weakly damped free electron system and the sharp onset ofd-band transitions. The possibility of enhancing the Kerr activity of amorphous TbFeCo alloys by Ag overlayers is also investigated.     

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利用朗缪尔探针和快速傅里叶变换研究了非平衡磁控溅射等离子体静电波动的驻波共振频谱特征。频带宽度为0~300kHz,典型放电条件下磁控靶前2cm和10cm两个位置的共振本征频率变化范围分别为10~50kHz和1~10kHz,研究了线圈电流、气压和放电功率等参数对共振本征频率的影响;指出了非平衡磁控溅射中能够导致等离子体静电驻波共振的两种势阱结构,提出驻波共振机制解释特征频率出现的原因,根据声驻波共振机制计算的电子温度数值符合实验的结果。     

非平衡磁控溅射等离子体频谱特征

利用朗缪尔探针和快速傅里叶变换研究了非平衡磁控溅射等离子体静电波动的驻波共振频谱特征。频带宽度为0~300kHz,典型放电条件下磁控靶前2cm和10cm两个位置的共振本征频率变化范围分别为10~50kHz和1~10kHz,研究了线圈电流、气压和放电功率等参数对共振本征频率的影响;指出了非平衡磁控溅射中能够导致等离子体静电驻波共振的两种势阱结构,提出驻波共振机制解释特征频率出现的原因,根据声驻波共振机制计算的电子温度数值符合实验的结果。     

Dusty photoresonant plasma with coulomb collisions

We have studied the charging of dust particles in a dense photoresonant sodium plasma with electron and ion densities as high as 10¹⁶ cm^?3 produced by laser pumping of the resonance level of Na, which was a small admixture (up to 1%) in an argon buffer gas. We show that the charge of dust particles with a radius of 10 mm at maximum reaches 3 × 10⁵ electron charges and that the potential of the dust particles at a low electron bulk loss rate agrees well with the orbital motion limited (OML) model data. The behavior of the electric field near a dust particle was found to be nonmonotonic. We established that the distribution of the potential near a solitary charged dust particle agrees well with the Debye one, but the screening length proves to be much larger than even the electron Debye length; the discrepancies are largest at the afterglow stage of the photoresonant plasma, when the sodium ion with a low recombination coefficient is the main plasma ion. We determined the domain of parameters for a dense plasma where an ensemble of dust particles can crystallize.     

Toroidal plasma resonances and electron transit time damping for heating large thermonuclear tori

We advocate a new method consisting of combining the large amplification of the r.f. field strength inside the plasma due to a magnetosonic resonance or to a torsional wave resonance of the toroidal cavity with its collision-less damping resulting from electron transit time damping.     

Diagnostic of capacitively coupled radio frequency plasma by homogeneous discharge model

In this Letter, a plasma diagnostic technique is reported to evaluate the plasma parameters of capacitively coupled radio frequency argon plasma on the basis of homogeneous discharge model. The technique is implemented for wide range of operating pressure ranging from few mTorrs to atmospheric pressure. Considerable dependence of plasma parameters on the plasma series resonance effect and the drift velocity of the electron for low pressure plasma and on the ion density for atmospheric pressure plasma jet were observed.     

Influence of noble gases on electron cyclotron heated hydrogen plasma

A quartz-chamber 2.45-GHz electron cyclotron resonance ion source (ECRIS) is designed at Peking University for the diagnostic purpose. Experimental results show that the added noble gases in hydrogen could cause a decrease of electron temperature and an increase of electron density. In this work, a numerical model is upgraded for ECR plasma generated by mixed gases. On this basis, the model is applied for the composed hydrogen plasma with additional noble gases. And dependences of neutral gas density and electron density on electron temperature are presented for individual gas (He, Ar, and H₂) and gas mixture, respectively. The calculated results are basically in accordance with the diagnostic results of ECRIS.     

Microwave power coupling with electron cyclotron resonance plasma using Langmuir probe

Electron cyclotron resonance (ECR) plasma was produced at 2.45 GHz using 200–750 W microwave power. The plasma was produced from argon gas at a pressure of 2 × 10^???4 mbar. Three water-cooled solenoid coils were used to satisfy the ECR resonant conditions inside the plasma chamber. The basic parameters of plasma, such as electron density, electron temperature, floating potential, and plasma potential, were evaluated using the current–voltage curve using a Langmuir probe. The effect of microwave power coupling to the plasma was studied by varying the microwave power. It was observed that the optimum coupling to the plasma was obtained for ~ 600 W microwave power with an average electron density of ~ 6 × 10¹¹ cm^???3 and average electron temperature of ~ 9 eV.