Numerical Approach of Interactions of Proton Beams and Dense Plasmas with Quantum-Hydrodynamic/Particle-in-Cell Model

A one dimensional quantum-hydrodynamic/particle-in-cell(QHD/PIC) model is used to study the interaction process of an intense proton beam(injection density of 1017cm~(-3))with a dense plasma(initial density of ~ 1021cm~(-3)), with the PIC method for simulating the beam particle dynamics and the QHD model for considering the quantum effects including the quantum statistical and quantum diffraction effects. By means of the QHD theory, the wake electron density and wakefields are calculated, while the proton beam density is calculated by the PIC method and compared to hydrodynamic results to justify that the PIC method is a more suitable way to simulate the beam particle dynamics. The calculation results show that the incident continuous proton beam when propagating in the plasma generates electron perturbations as well as wakefields oscillations with negative valleys and positive peaks where the proton beams are repelled by the positive wakefields and accelerated by the negative wakefields. Moreover, the quantum correction obviously hinders the electron perturbations as well as the wakefields. Therefore, it is necessary to consider the quantum effects in the interaction of a proton beam with cold dense plasmas, such as in the metal films.     

Dust Acoustic Compressive Waves in a Warm Dusty Plasma Having Non-Thermal Ions and Non-Isothermal Electrons

In this article an investigation is presented on the properties of dust acoustic(DA)compressive solitary wave propagation in an adiabatic dusty plasma,including the effect of nonthermal positive and negative ions and non-isothermal electrons.The reductive perturbation method has been employed to derive the lower degree modified Kadomtsev-Petviashivili(mK-P),3D Schamel-Korteweg-de-Vries equation or modified Kadomtsev-Petviashivili(mK-P) equations for dust acoustic solitary waves in a homogeneous,unmagnetized and collisionless plasma whose constituents are non-isothermal electrons,singly charged positive and negative non-thermal ions and massive charged dust particles.The stationary analytical solutions of the lower degree mK-P and mK-P equations are numerically analyzed,where the effect of various dusty plasma constituents on DA solitary wave propagation is taken into account.It is observed that both the ions in dusty plasma play a key role in the formation of DA compressive solitary waves,and also the ion concentration and non-isothermal electrons control the transformation of the compressive potentials of the waves.     

Ion Acoustic Solitary Waves and Double-Layers in a Plasma with Nonthermal Electrons and Positrons

The effects of nonthermal electron distribution and ion temperature are incorporated in the investigation of nonlinear ion acoustic waves in a pair-ion plasma. Sagdeev pseudo- potential method which takes into account the full nonlinearity of the plasma equations is used to study solitary wave solutions. It is shown that there is a region in parameter space where both negative and positive potential can coexist. For the fixed value of nonthermal electrons, it is found that the effect of increase in ion temperature is to reduce the range of co-existence of compressive and rarefactive solitons. Particular concentration of nonthermal electrons results in disappearance of rarefactive solitons while the decrease in ion temperature, at this concentration restores the lost rarefactive solitons. Also, the existence of rarefactive double layers solitons is investigated. It is found that the nonthermal electrons and ion-temperature play significant role in determining the region of the existence of double layers.     

平行极板间等离子体RF共振特性研究

为探索用于ＡＶＬＩＳ的更为有效的离子引出方法,对等离子的ＲＦ共振离子出引方法进行了理论研究,用ＰＩＣ方法对其了模拟。结果表明：在弱磁场下可产生鞘层－等离子体振荡,其振荡频率与理论一致;外加与振荡频率王牟的交流电压后将发生共振,其振荡幅度大幅增加,电流加大,共振在等离子体中产生的最大电位幅可高于外加电压幅度几倍;与离子引出方法中传统的平行板电场相比,ＲＦ共振法使得出出的离子流加大,离子引出时间显著     

Dust acoustic shock waves in magnetized dusty plasma

We have presented a theoretical study of the dust acoustic(DA) shock structures in a magnetized,electron depleted dusty plasma in the presence of two temperature superthermal ions. By deriving a Korteweg–de Vries–Burgers equation and studying its shock solution, we aim to highlight the effects of magnetic field and obliqueness on various properties of the DA shock structures in the presence of kappa-distributed two temperature ion population. The present model is motivated by the observations of Geotail spacecraft in the Earth?s magnetotail and it is seen that the different physical parameters such as superthermality of the cold and hot ions, the cold to hot ion temperature ratio, the magnetic field strength, obliqueness and the dust kinematic viscosity greatly influence the dynamics of the shock structures so formed. The results suggest that the variation of superthermalities of the cold and hot ions have contrasting effects on both positive and negative polarity shock structures.Moreover, it is noted that the presence of the ambient magnetic field affects the dispersive properties of the medium and tends to make the shock structures less wide and more abrupt. The findings of present investigation may be useful in understanding the dynamics of shock waves in dusty plasma environments containing two temperature ions where the electrons are significantly depleted.     

Mechanisms of Streamer Propagation Affected by Driven Voltage Polarity in a Cold Atmospheric Pressure Plasma Jet

A two-dimensional self-consistent fluid model is used to investigate the effects of DC-voltage polarity in plasma initiation and propagation of helium plasma jet.The simulation results indicate that the difference in initial breakdown for the positive jet and negative jet leads to a difference in the electron density of about 4 orders of magnitude,even with the same initial electric field,which also influences the subsequent propagation.In the propagation process of negative jets,the ionization process exists in a longer gas channel behind the streamer head.In addition,the drift process to the infinite grounded electrode driven by the electric field results in higher energy consumption in the ionization process.However,in the positive jet,the ionization process mainly exists in the streamer head.Therefore,the differences in the initial breakdown and propagation process make the electric field intensity and the ionization weaker in the streamer head of the negative jet,which explains the weaker and shorter appearance of the negative jet compared to the positive jet.Our model can adequately reproduce the experimental results,viz.a bullet-like propagation in the positive jet and a continuous plasma plume in the negative jet.Furthermore,it also indicates that the streamer velocity shows the same variations as the electron drift velocity for both positive and negative jets.     

离子初始速度对等离子体鞘层厚度的影响

本文从理论上研究了离子初始速度对等离子体鞘层厚度的影响,建立了理论计算公式和数值模拟方法,考察了离子初始速度对鞘层厚度的影响因子。在离子初始能量为3.2 eV情况下,用粒子模拟程序进行了数值模拟,模拟与理论计算得到的空间电场分布十分接近。     

Spherical and Cylindrical Ion Acoustic Shock Structures in Plasmas with q-Nonextensive Electron Velocity Distribution

The propagation of ion acoustic shock waves in cylindrical and spherical geometries has been investigated. The plasma system consists of cold ions, nonextensive electrons and thermal positrons. Spherical and cylindrical Korteweg–de Vries–Burger equations have been derived by reductive perturbation method and their shock behavior is studied by employing finite difference method. It is found that shock waves can be produced in this medium. The important effects of the q-nonextensive electron on the properties of ion acoustic waves are discussed. Furthermore, it is observed that the positron concentration, ratio of electron to positron temperature, geometry parameter and the plasma kinematic viscosity significantly modifies the shock structure.     

Breaking of a Langmuir wave in cold electron-positron-ion plasmas

The space-time evolution of a given density perturbation in cold homogeneous electron-positron-ion plasma is investigated with an assumption of infinitely massive ions by employing a numerical calculation method.The phase-mixing time and wave-breaking time can be effectively distinguished with this method.It is found that an increase of the ratio of equilibrium ion density to equilibrium electron density can attenuate plasma oscillations,leading to a delay in wave breaking.The dependence of the phase-mixing and wave-breaking times on the amplitude of the initial perturbation is also discussed.     

Modeling of Heat Fluxes in Edge Plasma of Small Size Divertor Tokamak

The heat flows out from the tokamak core region are collected on the divertor plates and external wall. Control of heat flux exhaust in the SOL and divertor plates regions is one of the important issues in tokamak physics. There are important phenomena affecting heat flows were simulated. The simulation is based on the B2SOLPS5.0 2D multifluid code. It is demonstrated that, the following results: (1) The simulation shows that, the operation of small size divertor tokamak, the divertor plate with/without impurities influence on profiles of electron, ion temperatures, and heat loads significantly. (2) Under normal direction of parallel (toroidal) magnetic field and different values of edge plasma density, strong “SOL” heat flow exists directed towards the LFS (outer) plate. (3) The simulation results show that, the increasing of the plasma density strong influence on the ion and electron poloidal heat fluxes profile significantly. The ion and electron polodial heat flux increase by factor “~8” and “2.4” times. (4) The simulation results show that the in–out asymmetry of heat fluxes was reversed when switching on/off E × B drifts in the edge plasma of this tokamak. (5) The simulation results show correlation between the in–out asymmetry divertor heat fluxes and E × B drift velocity. (6) The observed heat loads asymmetry between HFS and LFS plates can be explained with the radial electric field in SOL. (7) Also the simulation results performed result in, the in–out asymmetry strong influence on the characteristic length of ion poloidal heat flux.     

Effect of Internal Antenna Coil Power on the Plasma Parameters in13.56 MHz/60 MHz Dual-Frequency Sputtering

The plasma property of a hybrid ICP/sputtering discharge driven by 13.56 MHz/60 MHz power sources was investigated by Langmuir probe measurement. For the pure sputtering discharge, the low electron density and ion flux, the rise of floating potential and plasma potential with increasing power, as well as the bi-Maxwellian distribution of electron en- ergy distributions （EEDFs） were obtained. The assistance of ICP discharge led to the effective increases of electron density and ion flux, the suppression of rise of floating potential and plasma potential, as well as the change of EEDFs from bi-Maxwellian distribution into Maxwellian dis- tribution. The increase of electron density and ion flux, and the EEDFs evolution were related to the effective electron heating by the induced electric field.     

Method and experimental arrangement for Al thin film deposition from r.f. metal plasma with simultaneous self-ion bombardment

A method, experimental arrangement, and some particular details of the process for Al thin film deposition from r.f. metal plasma are described in this paper. In the plasma deposition system, Al is evaporated by an electron beam, partial ionization of the vapor is realized in r.f. inductive metal plasma, and film deposition is accompanied by simultaneous self-ion bombardment (SSIB) in a high-vacuum environment. Special attention is given to the accurate determination of such basic physical parameters of the process as plasma potential, ion energy, fraction of ions in the total arrival flux, added (normalized) energy, and power density of the ion bombardment. It is concluded that the fraction of secondary neutral energetic atoms in the total flux can be neglected in the calculations of the basic deposition parameters. At the power density in excess of about 0.5 W/cm², the substrate temperature can rise up to the Al melting point (660°C) during deposition. An analysis of the main heat sources in the plasma deposition system is presented in the paper. It is found that the results of the computer simulation of the substrate temperature increase caused by ion bombardment have a very good agreement with demonstrated experimental data.     

Progress Toward Steady-State Operation on Tore Supra

Important technological and physics issues related to steady-state operation required for next step are being examined on Tore Supra,after a major upgrade of internal components in order to increase the heat extraction capability to 25 MW for 1000 s.Here,we show first experimental results,where all the plasma facing components were actively cooled during pulses exceeding four minutes,with reactor-relevant heat load.New physics was observed in non-inductively driven plasmas,including a stationary peaked radial profile of the plasma density generated by an anomalous inward pinch;and a regime characterized by sinusoidal oscillations of central electron temperature,governed by non-linear coupling between heat transport and plasma current analogous to a predator-prey mechanism.     

Characterization of heat transport dynamics in laser-produced plasmas using collective Thomson scattering: Simulation and proposed experiment

We propose an experiment in which the collective Thomson scattering lineshape obtained from ion acoustic waves is used to infer the spatial structure of local heat transport parameters and collisionality in a laser-produced plasma. The peak-height asymmetry in the ion acoustic wave spectrum will be used in conjunction with a recently developed model describing the effects of collisional and Landau damping contributions on the low-frequency electron density fluctuation spectrum to extract the relative electron drift velocity. This drift arises from temperature gradients in the plasma. The local heat flux, which is proportional to the drift, can then be estimated, and the electron thermal conductivity will be inferred from the relationship between the calculated heat flux and the experimentally determined temperature gradient. Damping of the entropy wave component at zero mode frequency is shown to be an estimate of the ion thermal conductivity, and its visibility is a direct measure of the ion-ion mean free path. We also propose to measure thermal transport parameters under dynamic conditions in which the plasma is heated impulsively by a laser beam on a fast (50 ps) time scale. This technique will enable us to study heat transport in the presence of the large temperature gradients that are generated by this local heating mechanism. Deviations of the inferred local thermal conductivity from its Spitzer-Härm value can be used to study the transition to a nonlocal heat transport regime. We have constructed a simple numerical model of this proposed experiment and present the results of a simulation.This work was performed under the auspices of the U.S. Department of Energy by Sandia National Laboratories under Contract DE-AC04-94AL85000 and by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.     

Effect of Frequency and Power of Bias Applied to Substrate on Plasma Property of Very-High-Frequency Magnetron Sputtering

The effect of the frequency and power of the bias applied to the substrate on plasma properties in 60 MHz(VHF) magnetron sputtering was investigated.The plasma properties include the ion velocity distribution function(IVDF),electron energy probability function(EEPF),electron density n_e,ion flux Γ_i,and effective electron temperature T_(eff).These parameters were measured by a retarding field energy analyzer and a Langmuir probe in the 60 MHz magnetron sputtering,assisted with 13.56 MHz or 27.12 MHz substrate bias.The 13.56 MHz substrate bias led to broadening and multi-peaks IVDFs,Maxwellian EEPFs,as well as high electron density,ion flux,and low electron temperature.The 27.12 MHz substrate bias led to a further increase of electron density and ion flux,but made the IVDFs narrow.Therefore,the frequency of the substrate bias was a possible way to control the plasma properties in VHF magnetron sputtering.     

Characterization of high flux magnetized helium plasma in SCU-PSI linear device

A high-flux linear plasma device in Sichuan University plasma-surface interaction(SCU-PSI)based on a cascaded arc source has been established to simulate the interactions between helium and hydrogen plasma with the plasma-facing components in fusion reactors.In this paper,the helium plasma has been characterized by a double-pin Langmuir probe.The results show that the stable helium plasma beam with a diameter of 26 mm was constrained very well at a magnetic field strength of 0.3 T.The core density and ion flux of helium plasma have a strong dependence on the applied current,magnetic field strength and gas flow rate.It could reach an electron density of1.2?×?10~(19)m~(-3)and helium ion flux of 3.2?×?10~(22)m~(-2)s~(-1),with a gas flow rate of 4 standard liter per minute,magnetic field strength of 0.2 T and input power of 11 k W.With the addition of-80 Vapplied to the target to increase the helium ion energy and the exposure time of 2 h,the flat top temperature reached about 530°C.The different sizes of nanostructured fuzz on irradiated tungsten and molybdenum samples surfaces under the bombardment of helium ions were observed by scanning electron microscopy.These results measured in the SCU-PSI linear device provide a reference for International Thermonuclear Experimental Reactor related PSI research.     

Transient Behavior of Negative Hydrogen Ion Extraction from Plasma

For plasma source,the extraction of negative ions is quite diferent from that of positive ions.To understand the efect of extraction field on plasma,the time-dependent behavior of negative hydrogen ion extraction from a negative ion source has been studied by particle-in-cell simulation in the collisionless limit.The simulations have shown that,due to the diference in dynamics between electrons and ions,the imbalance of the numbers of charged particles occurs in the source,results in the broadening of plasma sheath and the great increase of plasma potential.The resultant high sheath field and the ambipolar electric field in plasma make the negatively charged particles congregate inside the sheath and move toward the extraction outlet.The emission area of negative ions is much smaller than that of the extraction aperture,which is in sharp contrast to the case of positive ion extraction.     

Head-on collision between single- and multi-soliton heavy ion acoustic waves in multi-ion plasmas

Head-on collisions among the single-and multi-soliton’s heavy ion acoustic waves (HIAWs) of multi-ion plasma are studied. The plasma consists of adiabatic positively charged inertial heavy ions, Boltzmann energy distributed light ions and kappa energy distributed electrons. The extended poincaré-Lighthill-Kuo (ePLK) method is applied for the derivation of two-sided Korteweg–de Vries (KdV) equations (KdVEs). The KdV single-soliton solutions (KdVSSs) are determined using the hyperbolic secant method and the KdV multi-soliton solutions (KdVMSs) are obtained using the Hirota method. The effects of superthermality of electrons, temperature ratios of electron to light ion and heavy ion to electron, and the density ratio of electron to heavy ion on phase shifts are investigated for the head-on collisions between two-soliton HIAWs. The effects of plasma parameters on angular frequency, phase speed, production of multi-soliton structures, and the head-on collisions among single-, double-, triple-, quadruple-, and quintuplesolitons are also studied.     

Dust Acoustic Shock Waves with Non-Thermal and Vortex-Like Ions in Dusty Plasma

A rigorous investigation is presented on the propagation characteristics of non-linear dust acoustic(DA)waves in an unmagnetized dusty plasma system containing non-thermal and vortex-like ions and Maxwellian electrons under the effect of a fluctuating charged dust fluid.The three-dimensional(3D)Burgers'equation and a new form of a lower degree modified 3D Burgers'equation with their analytical solutions are derived to study the features of shock waves in such plasmas.The effect of the population of non-thermal ions,the vortex-like ion parameter as well as the temperature ratios of ions and electrons on the evolution of shock waves in the presence of dust charge fluctuation is presented.This theoretical investigation might be effectively utilized to unveil the nature of many astrophysical plasma environments(Saturn's spokes etc.)where such plasmas are reported to have existed.     

Simulation of Small Size Divertor Tokamak Plasma Edge Including Self-Consistent Electric Fields

The B2.SOLPES.0.5.2D code (Braams, Contrib Plasma Phys 36:276, 1996; Rozhansky and Tendler, Rev Plasma Phys 19:147, 1996) is applied for modeling SOL (Scrape off Layer) plasma in the small size divertor tokamak. Detailed distributions of the plasma heat flux and other plasma parameters in SOL, especially at the target plate of the divertor are found by modeling. The modeling results show that most of the electron heat flux and small part of ion heat flux arrive at target plate of the divertor, while, a large part of the ion heat flux and part of electron heat flux arrive at the outer wall. Also analysis of the role of poloidal E × B drifts in the redistribution of edge plasma is fulfilled.