Interaction of plasma clusters with an axially symmetric magnetic field

The paper reports about measurements of the magnetic flux of a probe coil excited by a plasma cluster, moving in an axially symmetric magnetic field. The effective diamagnetic current, inductance and resistance of the cluster are derived from the dependence of the measured flux on the distance between the standard coil and the coil forming the magnetic field, as well as from the estimated main dimensions of the cluster.In conclusion the author wishes to express his thanks to Mr. J. Divíek for his devoted work in assembling the apparatus and to Mr, J. Bacílek for his work connected with the vacuum technique.     

A germanium oscillator in a pulsed magnetic field

Experimental data which confirms the presence of hysteresis of the magnetic threshold field of the helical instability of the plasma in a germanium oscillator are presented. It is shown that hysteresis of the threshold magnetic field is due to the inertia of the change in the effective lifetime of the charge carriers in the specimen when the magnetic field is increased and reduced. The dependence of the hysteresis of the threshold magnetic field on the electric field strength, the magnetic field, and the temperature is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–41, July, 1982.The authors thank R. I. Bashirov, and K. M. Aliev for making it possible to carry out the measurements in pulsed magnetic fields, and G. P. Il'yukevich for his technical help.     

Low-frequency instability of an inhomogeneous weakly ionized plasma in crossed electric and inhomogeneous magnetic fields

The paper discusses the drift dissipative instability that arises in a weakly ionized inhomogeneous plasma in crossed electric and magnetic fields. The potential perturbations are studied in the WKB (Wentzel-Krammers-Brillouin) approximation, i.e. for k = d lnn ₀/dx. The critical magnetic field, beyond the value of which the plasma is again stable against the studied perturbations, is computed. The effect of the inhomogeneity of the magnetic field modelled by a gravitational field is analyzed and the effect of a magnetic field, growing in the direction opposite to that of the plasma density, is pointed out. Under certain circumstances similar phenomena also arise in the current-convective instability.The author wishes to express his thanks to J. Václavík, K. Jungwirth and J. Preinhaelter for their stimulating discussions and comments.     

Secular free solution up to third-order of relativistic hot dissipative plasma equation for electrostatic field

The perturbation method of Lindstedt is applied to study the relativistic nonlinear effects for longitudinal electrostatic waves in a hot dissipative plasma having no static electric or magnetic field. Amplitude dependent frequency and wave-number shifts are derived including relativistic corrections.The author expresses his gratitude to Dr. B.Chakraborty of the Department of Mathematics, Jadavpur University, Calcutta for his guidance in the preparation of this paper and also wishes to thank Dr. K. P.Das of the Department of Mathematics, Kalyani University, Kalyani, for helpful discussions.     

Magnetogravitational instability of a rotating homogeneous gas cloud with radiation

Magnetogravitational instability of an infinite, homogeneous rotating hot plasma cloud associated with radiative processes has been studied with the help of relevant MHD equations using normal mode analysis. Rotation is taken parallel and perpendicular to the magnetic field for both, the longitudinal and transverse modes of propagation. The Jeans espression of instability is modified to give the stabilizing effect of radiation pressure. The stabilizing effect of magnetic field is observed only for transverse mode of propagation whereas rotation stabilizes only along the magnetic field for transverse mode. The stabilizing effect of rotation is comparatively more effective.D. S. Vaghela gratefully acknowledges the financial assistance for his minor research project given by University Grants Commission of India.     

以巨脉冲红宝石激光为光源的Mach-Zehnder干涉仪应用于θ收缩等离子体的研究

本文应用巨脉冲红宝石激光为光源的Mach-Zehnder干涉仪,研究了23kJ(千焦耳)“θ收缩”(θ-pinch)等离子体的电子密度、形状和不稳定性。从轴向干涉图的照片获得45至120mTorr(毫乇)氘气压范围的二维电子密度分布和电子密度的峰值在6×10¹⁶—2.3×10¹⁷cm^-3范围。等离子体最大收缩出现在主压缩磁场的第一个半周期的1/3附近,在等离子体的最大收缩附近的特征约束时间(粒子数衰减1/e的时间)为1.8—4.3μs,具有负偏磁场的干涉图显示在等离子体中捕获了偏磁场。从这些干涉图的照片上还看到等离子体在主压缩磁场和等离子体捕获场之间作径向磁流体振荡。干涉图照片还表明,在45至80mTorr氘气压范围内,等离子体在主压缩磁场的第一个半周期内基本上都是稳定的。     

Rotational properties of annulus dusty plasma in a strong magnetic field

The collective dynamics of an annulus dusty plasma formed between a co-centric conducting (non-conducting) disk and ring configuration is studied in a strongly magnetized radiofrequency (rf) discharge. A superconducting electromagnet is used to introduce a homogeneous magnetic field to the dusty plasma medium. In the absence of the magnetic field, the dust grains exhibit thermal motion around their equilibrium position. The dust grains start to rotate in the anticlockwise direction with increasing magnetic field (B > 0.02 T ), and the constant value of the angular frequency at various strengths of the magnetic field confirms the rigid body rotation. The angular frequency of dust grains linearly increases up to a threshold magnetic field (B > 0.6 T ) and after that its value remains nearly constant in a certain range of magnetic field. Further increase in magnetic field (B > 1 T ) lowers the angular frequency. Low value of the angular frequency is expected by reducing the width of the annulus dusty plasma or the input rf power. The azimuthal ion drag force due to the magnetic field is assumed to be the energy source which drives the rotational motion. The resultant radial electric field in the presence of a magnetic field determines the direction of rotation. The variation of floating (plasma) potential across the annular region at given magnetic field explains the rotational properties of the annulus dusty plasma in the presence of a magnetic field.     

The influence of the increase in inductance at the acceleration of plasma in an external magnetic field

The paper deals with the accelerating influence of an external perpendicular constant magnetic field on the acceleration of plasma clusters. Assuming that the increase in inductance, caused by the motion of the cluster, plays a relatively small role, approximate solutions are found for the current and velocity by expanding the solution into power series with respect to a small parameter which characterizes the increase in inductance.In conclusion, the author thanks Professor Kracík for his interest and aid in the work.     

Magnetic field generated in a plasma by a short, circularly polarized laser pulse

We study the generation of a quasistatic magnetic field by a short, circularly polarized laser pulse in a tenuous cold uniform plasma. It is shown that two physical mechanisms are responsible for the generation of the various components of the magnetic field. One mechanism is due to the ponderomotive forces and governs the generation of the azimuthal component of the magnetic field. The other is similar to the inverse Faraday effect (IFE) in a nonuniform plasma and gives rise to axial and radial components of the magnetic field. At moderate radiative intensities, all magnetic field components are proportional to the squared intensity. The spatial structure of the magnetic field depends strongly on the pulse shape and the plasma density. Zh. éksp. Teor. Fiz. 114, 849–863 (September 1998)     

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100?50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient α _B has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in α _B and this decrease can be several orders of magnitude.     

Voltage of the vacuum arc with a ring anode in an axial magneticfield

The plasma jet focusing and voltage distribution in the interelectrode gap of a vacuum arc with a ring anode and subjected to an axial magnetic field were studied theoretically. A two-dimensional model was developed based on the free plasma jet expansion into vacuum, and the steady-state solution of the fully ionized plasma in the hydrodynamic approximation was analyzed. It was found that the imposition of an axial magnetic field reduces the radial expansion of the plasma jet. The characteristic jet angle decreases from about 40° in the zero magnetic field case and approaches a value of about 20° with a 0.02 T magnetic field. The arc voltage consisting of the cathode drop, the plasma voltage drop, and anode sheath drop increased, with the imposition of a magnetic field, and decreased with the anode length. The model was compared to experimental measurements of the vacuum arc voltage behavior in an axial magnetic field, and good agreement was found     

Guiding of an electromagnetic pulse in a plasma immersed in combined wiggler and axial magnetic fields

We present a new plasma-based method of guiding an electromagnetic pulse. The scheme consists of an inhomogeneous magnetic field and a uniform density plasma, in contrast to existing schemes that rely on transverse plasma density gradients but need not be magnetized. The refractive index of a magnetized plasma depends on the strength and direction of the magnetic field as well as the plasma density. A guiding channel is formed by using field inhomogeneity to generate the desired transverse profile of the index of refraction. The concept is analyzed with an envelope equation and, for the specific example of a wiggler magnetic field, with a two-dimension particle-in-cell simulation. A simplified model of this scheme as producing a magnetic wall in analogy to metallic waveguides is presented, for which corresponding approximate relations for the guided mode axial wavelength and radius are derived as functions of the plasma and magnetic field parameter. These are seen to be in good agreement with particle-in-cell simulation results. Since the desired inhomogeneity of the refractive index can be made easily when the electromagnetic wave frequency is close to the cyclotron frequency, this guiding scheme is most readily applied in the microwave regime.     

Non-equilibrium statistical mechanics of synchrotron-Cerenkov radiation

The synergic synchrotron-Cerenkov (SC) radiation emitted by a relativistic charged particle under the combined effect of the constant external magnetic field and the collective interactions in the ambient plasma (medium) is given in the framework of the non-equilibrium statistical mechanics developed by Prigogine and his co-workers. Starting from the formal solution of the Liouville equation, the one-particle distribution function is calculated. Restricting the motion of the test particle to a circular orbit in the plane normal to the magnetic field, we use the above distribution function to calculate the power emitted per unit solid angle by the test particle as a function of time. We have thus obtained the time evolution of the synergic SC radiation which in the asymptotic limit reproduces the results of Schwinger and his co-workers. It is also shown that the collective interactions within the system produces a shift in the frequency of the outcoming radiation.     

Magnetic properties of a nearly classical one-component plasma in three or two dimensions: II. Strong field

The equilibrium statistical mechanics of a nearly classical one-component plasma, submitted to a strong magnetic field, is studied, in three or two dimensions, by a suitable expansion of the Wigner distribution function. A strong magnetic field quenches the quantum fluctuations transverse to the field. The situation is especially simple for a two-dimensional plasma, which has a classical behaviour in the strong-field limit; as a consequence, a classical Wigner crystallization can be induced by the magnetic field.     

外加磁场微波等离子推力器内流场数值模拟

为了提高微波等离子推力器性能，改善等离子体对电磁波能量的吸收状况，提高核心区温度，提出外加磁场的方案，并对热等离子体进行了数值模拟.假设局域热平衡条件，采用Navier-Stokes，Maxwell和Saha方程，利用压力修正的半隐格式和时域有限差分求解方法，建立了径向磁镜场下推力器内等离子体流场的数值计算模型.数值模拟结果表明：外加磁场后的磁感应强度小于0.5 T时，推力器内热等离子体核心区最高温度随磁感应强度的增加而迅速提高.外加磁场后的磁感应强度大于0.5 T时，核心区最高温度随磁感应强度的增加而缓慢提高.磁感应强度为0.5 T时，热等离子体核心区最高温度与不加磁场相比提高了24%.外加磁场对等离子体流场速度分布影响不大. 关键词： 等离子体模拟 等离子体相互作用 等离子体流动     

有限磁场中等离子体圆柱波导的传播特性

分析了有耗介质中等离子体圆柱波导在有限外加磁场中的传播特性.重点讨论了波导传播常数随等离子体参数、介质参数和外加磁场的变化.分析结果表明，有限强磁场中的等离子体波导的传播特性比无外磁场或外加磁场为无穷大时具有更强的控制能力. 关键词：     

Strong space plasma magnetic barriers and Alfvénic collapse

High-magnitude magnetic barriers in space and solar plasma are proposed to be attributed to the pile up of magnetic field lines and their Alfvénic collapse for MHD flows. The analysis of experimental data from both the Interball and Cluster spacecrafts shows that high-magnitude magnetic structures found in the Earth magnetosheath and near the magnetopause are supported by a nearly thermal transverse plasma flow, with the minimum barrier width being on the order of the ion gyroradius. The collapse termination at such scales can be explained by the balance between the pile up of magnetic field lines and backward finite-gyroradius diffusion. Comparison between the theoretical, modeling, and experimental data shows that the Alfvénic collapse is, in general, a promising mechanism for magnetic field generation and plasma separation. The text was submitted by the authors in English.     

双等离子体团相互作用的磁流体力学模拟

利用商用磁流体力学模拟程序USIM对双等离子体团相互作用过程进行了数值模拟,分别考察和比较了双对流等离子体团在外加磁场和无外加磁场情况下,相互作用的物理过程.发现在外加磁场情况下等离子体团相互作用会伴随着磁重联(反向磁场)、磁排斥(同向磁场)以及一些不稳定过程.针对激光产生等离子体团错位相互作用实验,进行了标度模拟,发现外加磁场起着重要作用,进一步表明激光等离子体的磁化特征.研究结果为下一步在神光Ⅱ激光装置进行强磁环境下等离子体实验提供理论指导.     

Coaxial Discharge and Transverse Magnetic Field

The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (T_e). The experimental results and the calculations showed that T_e is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied.     

Plasma diffusion and transport in a magnetic duct filter

A cathodic arc plasma source equipped with a curved magnetic duct to filter macro-particles was used to study plasma diffusion and transport in the duct. We determine the optimal duct bias, at which the magnetic duct produces the maximum plasma output, for titanium cathodic arc plasma at 50, 100 and 150 A arc current, and we investigate the parametric effects of the arc current and guiding magnetic field on the optimal duct bias. The optimal bias decreases as the guiding magnetic field increases from 0.01 to 0.04T and is almost independent of the guiding magnetic field when the magnetic field strength ranges from 0.04 to 0.06T, the upper limit for our equipment. The optimal duct bias at 0.04T guiding magnetic field decreases with increasing arc current.