Effect of electron magnetic trapping in a plasma immersion ion implantation system

In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage of 10.0 kV is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform nitrogen plasma. A pair of external coils creates a static magnetic field with main vector component along the axial direction. Thus, a system of crossed E×B field is generated inside the vessel forcing plasma electrons to rotate in azimuthal direction. In addition, the axial variation of the magnetic field intensity produces magnetic mirror effect that enables axial particle confinement. It is found that high-density plasma regions are formed around the target due to intense background gas ionization by the trapped electrons. Effect of the magnetic field on the sheath dynamics and the implantation current density of the PIII system is investigated. By changing the magnetic field axial profile (varying coils separation) an enhancement of about 30% of the retained dose can be achieved. The results of the simulation show that the magnetic mirror configuration brings additional benefits to the PIII process, permitting more precise control of the implanted dose.     

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)     

Dielectric linear response of magnetized electrons: Drag force on ions

The drag force on ions moving in a magnetized electron plasma is calculated in dielectric linear response. Various representations of the dielectric function ε(k, ω) are investigated for their suitability to display the limits for an infinite and a vanishing magnetic field. While the influence of the magnetic field is negligible in certain regions of k-space, it introduces in other regions a strong oscillatory structure in the dielectric function. This requires a careful treatment of the multidimensional integrations necessary for the drag force. The contributions from oscillatory integrands are treated by the saddle point method. Explicit results are obtained for the dependence of the drag force on the magnetic field, the direction of motion of the ion relative to the magnetic field, the shielding in the electron plasma, its density and the anisotropy of the electron temperature. The importance of the collective response of the electrons is investigated for limiting cases of the magnetic field. The validity of the linearization of the dielectric theory is checked by comparison with results obtained by numerical simulation of the nonlinear Vlasov-Poisson equation. For strong magnetic fields and low ion velocities, the simulations rather agree with the complementary binary collision model than with linear response.     

Ion surface cyclotron waves at plasma-metal interfaces

The dispersion properties of slow electromagnetic surface waves propagating across a constant external magnetic field and along a plane plasma-metal interface at harmonics of the ion cyclotron frequency are studied. The motion of the plasma particles is described by a Vlasov-Boltzmann kinetic equation. The effects of the plasma size, the dielectric permittivity of the transition region between the plasma and metal, and the magnitude of the constant external magnetic field on the dispersion characteristics of ion surface cyclotron waves are studied. Zh. Tekh. Fiz. 69, 83–89 (October 1999)     

Magnetic trap for confining a hot plasma

The magnetic field of a two-helix Tornado trap has all the properties needed to efficiently confine a hot plasma. However, its practical utilization has been restricted because of the ponderomotive interaction between the turns of the helices, which disrupts the structure of the magnetic field. A modification of a Tornado trap, which permits significant reduction of the ponderomotive interaction is considered, and arguments in favor of using a magnetic field to maintain the properties of the field in an unmodified trap are presented. Zh. Tekh. Fiz. 67, 25–28 (September 1997)     

Initial Measurements of Plasma Potential in the Core of the MST Reversed Field Pinch with a Heavy Ion Beam Probe

Measurement of the plasma potential in the core of MST marks both the first interior potential measurements in an RFP, as well as the first measurements by a Heavy Ion Beam Probe (HIBP) in an RFP. The HIBP has operated with (20-110) keV sodium beams in plasmas with toroidal currents of (200-480) kA over a wide range of densities and magnetic equilibrium conditions. A positive plasma potential is measured in the core, consistent with the expectation of rapid electron transport by magnetic fluctuations and the formation of an outwardly directed ambipolar radial electric field. Comparison between the radial electric field and plasma flow is underway to determine the extent to which equilibrium flow is governed by E×B. Measurements of potential and density fluctuations are also in progress.Unlike HIBP applications in tokamak plasmas, the beam trajectories in MST (RFP) are both three-dimensional and temporally dynamic with magnetic equilibrium changes associated with sawteeth. This complication offers new opportunity for magnetic measurements via the Heavy Ion Beam Probe (HIBP). The ion orbit trajectories are included in a Grad-Shafranov toroidal equilibrium reconstruction, helping to measure the internal magnetic field and current profiles. Such reconstructions are essential to identifying the beam sample volume locations, and they are vital in MST's mission to suppress MHD tearing modes using current profile control techniques. Measurement of the electric field may be accomplished by combining single point measurements from multiple discharges, or by varying the injection angle of the beam during single discharges.The application of an HIBP on MST has posed challenges resulting in additional diagnostic advances. The requirement to keep ports small to avoid introducing magnetic field perturbations has led to the design and successful implementation of cross-over sweep systems. High levels of ultraviolet radiation are driving alternative methods of sweep plate operation. While, substantial levels of plasma flux into the HIBP diagnostic chambers has led to the use of magnetic plasma suppression.     

Effect of unstable MHD modes on the confinement of a stellarator plasma

The results of an experimental study of the influence of unstable MHD modes on plasma confinement in an L-2M stellarator are presented. The spectral and statistical characteristics of turbulent plasma simultaneously at both the edge and center of the plasma are investigated. It is shown that at constant power of electron-cyclotron heating of the plasma the energy content of the plasma depends strongly on the strength of the externally applied vertical magnetic field used to adjust the position of the plasma column. Appreciable degradation of plasma confinement is observed for values of the vertical field such that ideal MHD modes become unstable in the greater part of the plasma column. This in turn is due to the formation of a magnetic configuration with a magnetic “hump.” At the same time, in the edge plasma the instability of resistive-balloon modes grows, and turbulent particle transport increases. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 407–412 (25 March 1999)     

Interference simulation in a cold collisionless moving magnetized plasma slab and (free surface of plasma slab)

Abstract

The pattern of intensity due to the interference in a cold collisionless magnetized moving plasma slab is investigated. Theoretically, it is assumed the mentioned layer has been located as a thin layer in an etalon Fabry–Perot interferometer surrounded by vacuum. The direction of external magnetic field is normal to the plasma surface and the plasma slab moves parallel with external constant magnetic field. By taking into account the relativistic considerations, the functions of transmitted intensity are presented coincident with the Airy function form in laboratory and plasma slab frames, respectively. The effects of plasma frequency, cyclotron frequency, thickness of plasma slab, and velocity of the plasma slab on band width, finesse factor, and visibility are simulated. Finally with the assumption that there are two wavelengths near together in incident electromagnetic beam the power resolution for this configuration are analyzed. All studies mentioned above have been done for S-polarized and P-polarized electromagnetic beams separately.     

Ohm’s law in a chiral plasma

The motion of plasma electrons in a stochastic electromagnetic field is studied in the low-conductivity limit. It is shown that under very general conditions, in the presence of a nonzero average chirality of the small-scale electromagnetic field, the effective current depends on the curl of the applied electric field, j=§ E+§_κcurl E, just as for similar dependences for the electric displacement and magnetic induction vectors in optically active and artificial chiral media. Under certain conditions such an Ohm’s law leads to growth of the magnetic field, the structure of the growth being dependent on the conductivity of the medium. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 268–273 (25 August 1999)     

On the Gradient-Current Mechanism of Formation of the Irregular Structure of the High-Latitude Upper Ionosphere

We consider the gradient-current instability of an inhomogeneous magnetoactive plasma in the approximation of double-fluid magnetohydrodynamics. Unlike the known gradient-drift and current-convective instabilities, the gradient-current instability is related to generation of nonpotential quasistatic electric fields polarized orthogonal to the external magnetic field B ₀ and excited by eddy currents whose density vector lies in the plane passing through the vectors of the magnetic field B ₀ and large-scale electron-density gradient. It is shown that in the high-latitude upper ionosphere, in the regions containing large-scale currents flowing in and out of the ionosphere along the magnetic field, the gradient-current instability can lead to the appearance of sheet-like irregularities extended predominantly in the plane passing through the geomagnetic-field and regular plasma-drift velocity vectors. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 7, pp. 574–587, August 2005.     

Skin effect during propagation of high-power short-wavelength microwaves in a partially ionized semiconductor plasma

A study is made of the propagation of high-power electromagnetic waves in spatially inhomogeneous plasmas of thin semiconducting elements and films. The effect of surface recombination and an external magnetic field on the depth of penetration of an ionizing field into the semiconductor plasma is examined. Zh. Tekh. Fiz. 69, 135–136 (May 1999)     

Potential surface waves at the boundary of a metal with a magnetoactive plasma at finite pressure

The propagation of surface-type potential waves along the interfacial boundary of a plasma with an ideally conducting metal in an external magnetic field perpendicular to the boundary is examined. It is shown that a necessary condition for the existence of these waves in the system is a finite gas kinetic pressure. Dispersion relations for these waves and expressions for the penetration depth of the wave fields into the plasma are obtained, and they are studied numerically for various plasma parameters. The frequency region for propagation of these waves is found. It is also shown that in a nonzero external magnetic field a system of this kind has a range of frequencies in which the wave is a generalized surface wave. Zh. Tekh. Fiz. 69, 30–33 (November 1999)     

Ionization self-channeling of modulated plasma-wave beams in a magnetic field

The dynamics of ionization self-channeling of modulated beams of plasma waves forming a solitary plasma-wave channel in an external magnetic field is investigated. It is shown that electromagnetic wave processes at the modulation frequencies of the ionizing radiation can be excited in the background plasma and in the channel. Zh. éksp. Teor. Fiz. 113, 1289–1298 (April 1998)     

Generation of electromagnetic waves by a rotating plasma

Generation of electromagnetic waves by an annular shell of plasma rotating in crossed radial electrostatic and axial magnetic fields in a cylindrical resonator is investigated theoretically. Dispersion relations are obtained describing the interaction of the waves with the plasma. It is shown that generation of waves by a narrow plasma shell is possible due to a cyclotron resonance, Čerenkov resonance, or plasma resonance. Here we consider a Čerenkov resonance, where the velocities of the plasma components and the phase velocities of the waves are perpendicular to the constant magnetic field. The frequencies and growth rates of the waves are found under conditions of the above-mentioned resonances in a uniform and in a nonuniform plasma shell. Advantages and disadvantages of wave generation under various conditions are noted. Zh. Tekh. Fiz. 69, 16–21 (February 1999)     

Magnetoacoustic solitons in pair-ion fullerene plasma

ABSTRACT

The propagation of magnetoacoustic (fast magnetohydrodynamic) waves in pair-ion (PI) fullerene plasma is studied in the linear and nonlinear regimes. The pair-ion (PI) fullerene plasma is theorized as homogeneous, magnetized, warm and collisionless. Employing multi-fluid magnetohydrodynamic model, the dispersion relation is obtained and wave dispersion effects which appear through ion inertial length are discussed. Using reductive perturbation technique (RPT), the Korteweg–de Vries (KdV) equation is derived and its solution for small but finite amplitude magnetoacoustic solitons propagating in the direction perpendicular to the external magnetic field is presented. The compressive magnetoacoustic soliton (i.e. positive potential pulse) propagating with super Alfvénic speed is obtained in magnetized PI fullerene plasma. The variations in the amplitude and width of the magnetoacoustic soliton structures are also illustrated by using numerical values of the plasma parameters such as ions' density, temperature difference between fullerene ions and magnetic field intensity, which have been taken from the PI plasma experiments already published in the literature.     

Generation of electromagnetic waves by relativistic electrons in a cavity with crossed radial electrostatic and axial magnetic fields under plasma resonance conditions

A theoretical analysis is made of the conditions for generation of electromagnetic waves by a thin cylindrical layer of relativistic electrons rotating in crossed axial magnetic and radial electrostatic fields in a cylindrical cavity. A dispersion equation is obtained to describe the interaction between waves and electrons under plasma resonance conditions. The dependence of the growth rates on the relativistic factor and the magnetic field are studied. Zh. Tekh. Fiz. 69, 112–114 (June 1999)     

Hysteresis in the presence of electron-cyclotron resonance

A method of determining the nonlinear interaction of microwaves with a magnetoactive lowpressure plasma is presented. It is shown by solving simultaneously the problems of the propagation of electromagnetic waves, the balance of charged particles, and the energy balance that near a critical value of the constant magnetic induction the character of the interaction of the wave and the plasma changes substantially: For magnetic fields above the critical field a much stronger interaction is observed, for which the penetration depth of the incident wave into the plasma increases. An investigation of the strong interaction regime showed the existence of hysteresis, which is accompanied by an abrupt transition from one standing-wave mode in plasma to another. It is shown that virtually complete absorption of the wave is possible. Zh. Tekh. Fiz. 69, 31–37 (December 1999)     

Formation of tight plasma pinches and generation of high-power soft x-ray radiation pulses in fast Z-pinch implosions

Argon K-shell plasma radiation source experiments were carried out on the GIT-12 generator [Bugaev, S.P. et al., 1997, Russian Phys. Journal, 40, 38] for a long (300 ns) implosion regime. The performance of a shell-on-solid-fill double gas puff was characterized in the experiments with and without an external axial magnetic field. The maximum Ar K-shell radiation yield registered in the experiments without an axial magnetic field was at the level of 1100 J/cm. This yield is consistent with the theoretically predicted yield for a short (100 ns) implosion regime. The experiments showed that the initial magnetic field which provides stabilization of the shell-on-solid-fill double gas puff was lower than that required for stabilization of a single annular gas puff. Satisfactory stabilization of the double gas puff was observed at an initial axial magnetic field of 1.4 kG. The maximum Ar K-shell radiation yield registered in the experiments with the axial magnetic field did not exceed 400 J/cm. A sharp reduction of the K-shell yield cannot be explained only by taking into account the energy losses associated with the compression of the axial magnetic field. Original Text ? Astro, Ltd., 2006.     

The strongest magnetic barrier in the DIII-D tokamak and comparison with the ASDEX UG

Magnetic perturbations in tokamaks lead to the formation of magnetic islands, chaotic field lines, and the destruction of flux surfaces. Controlling or reducing transport along chaotic field lines is a key challenge in magnetically confined fusion plasmas. A local control method was proposed by Chandre et al. [Nucl. Fusion 46, 33–45 (2006)] to build barriers to magnetic field line diffusion by addition of a small second-order control term localized in the phase space to the field line Hamiltonian. Formation and existence of such magnetic barriers in Ohmically heated tokamaks (OHT), ASDEX UG and piecewise analytic DIII-D [Luxon, J.L.; Davis, L.E., Fusion Technol. 8, 441 (1985)] plasma equilibria was predicted by the authors [Ali, H.; Punjabi, A., Plasma Phys. Control. Fusion 49, 1565–1582 (2007)]. Very recently, this prediction for the DIII-D has been corroborated [Volpe, F.A., et al., Nucl. Fusion 52, 054017 (2012)] by field-line tracing calculations, using experimentally constrained Equilibrium Fit (EFIT) [Lao, et al., Nucl. Fusion 25, 1611 (1985)] DIII-D equilibria perturbed to include the vacuum field from the internal coils utilized in the experiments. This second-order approach is applied to the DIII-D tokamak to build noble irrational magnetic barriers inside the chaos created by the locked resonant magnetic perturbations (RMPs) (m, n)=(3, 1)+(4, 1), with m and n the poloidal and toroidal mode numbers of the Fourier expansion of the magnetic perturbation with amplitude δ. A piecewise, analytic, accurate, axisymmetric generating function for the trajectories of magnetic field lines in the DIII-D is constructed in magnetic coordinates from the experimental EFIT Grad-Shafranov solver [Lao, L, et al., Fusion Sci. Technol. 48, 968 (2005)] for the shot 115,467 at 3000 ms in the DIII-D. A symplectic mathematical map is used to integrate field lines in the DIII-D. A numerical algorithm [Ali, H., et al., Radiat. Eff. Def. Solids Inc. Plasma Sc. Plasma Tech. 165, 83 (2010)] based on continued fraction decomposition of the rotational transform labeling the barriers for selecting and identifying the strongest noble irrational barrier is used. The results are compared and contrasted with our previous results on the ASDEX UG. About six times stronger a barrier can be built in the DIII-D than in the ASDEX UG. High magnetic shear near the separatrix in the DIII-D is inferred as the possible cause of this. Implications of this for the DIII-D and the International Thermonuclear Experimental Reactor (ITER) are discussed.     

Dynamic model for plasma opening switches

A dynamic model for plasma opening switches is proposed. The basis of the model is the appearance and development of force instabilities (pinch and sausage) in a spatially nonuniform plasma accelerated by a magnetic field as a driver piston. The proposed model does not require the invocation of subtle effects in the pinch collapse phase and makes it possible, without going beyond the framework of magnetohydrodynamics, to explain the principal operating features of plasma opening switches and to obtain quantitative estimates consistent with experiment. Zh. Tekh. Fiz. 69, 25–29 (May 1999)