Conversion of plasma energy into electrical pulse by magnetic flux compression

A conceptual study of magnetic flux compression inside a cylindrical coil by an expanding inertial fusion plasma sphere across the magnetic field produced by the coil itself have been performed numerically using a two-dimensional magnetohydrodynamic (MHD) simulations. The concept may find application in inertial fusion energy (IFE) system as a direct energy conversion scheme to convert a part of fusion plasma kinetic energy into pulsed electrical energy. Important theoretical and technical issues that has to be addressed are discussed. Preliminary theoretical analysis are given for the analysis of MHD interchange instabilities of expanding plasma across magnetic field. Overall efficiency of the system is determined numerically for a typical set of initial plasma and system parameters. Ultrahigh coil inter-turn voltages are predicted. Therefore, the application of magnetic self-insulation to avoid coil inter-turn break-down is considered. Also, we have analysed the system performance with different load conditions.     

Numerical and experimental investigation of plasma plume deflection with MHD flow control

This paper presents a composite magneto hydrodynamics(MHD) method to control the lowtemperature micro-ionized plasma flow generated by injecting alkali salt into the combustion gas to realize the thrust vector of an aeroengine.The principle of plasma flow with MHD control is analyzed.The feasibility of plasma jet deflection is investigated using numerical simulation with MHD control by loading the User-Defined Function model.A test rig with plasma flow controlled by MHD is established.An alkali salt compound with a low ionization energy is injected into combustion gas to obtain the low-temperature plasma flow.Finally,plasma plume deflection is obtained in different working conditions.The results demonstrate that plasma plume deflection with MHD control can be realized via numerical simulation.A low-temperature plasma flow can be obtained by injecting an alkali metal salt compound with low ionization energy into a combustion gas at 1800–2500 K.The vector angle of plasma plume deflection increases with the increase of gas temperature and the magnetic field intensity.It is feasible to realize the aim of the thrust vector of aeroengine by using MHD to control plasma flow deflection.     

Simulation Research of Magnetic Constriction Effect and Controlling by Axial Magnetic Field of Vacuum Arc

Based on magnetohydrodynamic (MHD) model of vacuum arc, the computer simulation of vacuum arc was carried out in this paper. In the MHD model, mass conservation equation, momentum conservation equations, energy conservation equations, generalized ohm‘s law and Maxwell equation were considered. MHD equations were calculated by numerical method, and the distribution of vacuum arc plasma parameters and current density were obtained. Simulation results showed that the magnetic constriction effect of vacuum arc is primarily caused by the Hall effect. In addition, the inhibition of axial magnetic field (AMF) on constriction of vacuum arc was calculated and analyzed.     

Combining the “Kinetic Tandem” and the “Kinetic Stabilizer” Concepts

A novel means of MHD stabilizing axially symmetric mirror systems was proposed by Ryutov and demonstrated in the Gas Dynamic Trap at Novosibirsk. It relies on the strongly stabilizing effect exerted by low density plasma on the expanding field lines outside the mirrors. The “Kinetic Stabilizer Tandem Mirror” implements Ryutov’s technique by injecting axially directed ion beams into the expander. The ions, stagnated, and reflected by the converging magnetic field, form the stabilizing plasma. MHD stability code calculations show stabilization at beta values of 40%, with stabilizer beam powers that are small compared to the T-M fusion power output. Implicit in the calculations is the assumption that adequate “communication” exists between the plug plasmas and the stabilizer plasmas. This paper examines one means for enhancing communication: Utilize the stabilizer plasma to create a potential peak that, together with the plug potential, forms a potential well that traps and contains a “bridging” plasma.     

Numerical simulation of low-current vacuumarc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. In this condition, the arc is in the diffuse mode. The appearance of the plasma jet calculated in the model is consistent with the experimental results.     

Quantitative determination of magnetic fields on object surfaces via photoemission electron microscopy without restriction of the electron beam

The stray magnetic field of domains on the surface of Nd₁₇Fe₁₇Cu₅B₅ and SmFe₁₀Ti₈₉ samples was visualized by emission electron microscopy in the regime without restriction of the electron rays by a contrast aperture. The distribution of the tangential and normal components of the magnetic field on the surface under study was derived from the image contrast. The experimental uncertainty of the performed quantitative measurements of the magnetic field is estimated as 15-20%, however, the applied technique has a principal error that is several times smaller.     

Controlled magnetohydrodynamic mode sustainment in the reversed-field pinch: Theory, design and experiments

A novel control system design for magnetohydrodynamic (MHD) resistive-wall mode (RWM) stabilization is developed from the viewpoint of process control. The engineering approach assumed consists of system identification, selection of feedback interconnections, and subsequently, associated feedback gain tuning. A design for general output tracking is devised, implemented and experimentally verified to be capable of sustaining MHD modes in the reversed-field pinch (RFP) machine EXTRAP-T2R. In principle, by active feedback, the plasma column boundary is forced to ‘user-specified’ helicities of prescribed amplitudes and phases. Experimental success is mainly attributed to careful identification of local magnetic field diffusion time-constants, and individual actuator channel peripheral dynamics. Addition of functionality and key features of this new MHD feedback system software might provide a versatile tool for experimental plasma dynamics and innovative MHD stability research.     

Plasma MHD generator for modelling energy conversion in pulsed thermonuclear reactors

Conclsuions The construction of an experimental model for studying MHD energy conversion from a pulsed thermonuclear reactor is a realistic technical task at the present time. Doing this would permit development of a large scale MHD generator module for the typical parameters of the heated working medium in a pulsed thermonuclear reactor.In principle it is possible to obtain an efficiency of at least about 40% with a linear plasma MHD generator. The efficiency of the whole plant might be increased further by utilization of the thermal energy at the outlet of the MHD channel in traditional methods.When such an MHD generator is built difficulties with the behavior of supersonic plasma streams undergoing strong velocity reduction in a channel and the associated gasdynamic problems can clearly be solved successfully by active modification of the boundary layer and appropriate profiling of the MHD channel. Some complications may arise if a regime with time varying magnetic braking is used. Also important is the problem of the behavior of the plasma stream at large magnetic Reynolds numbers (Re_m1).The basic technological problems are these: materials for the MHD channel, cooling arrangements for the channel (especially the critical cross section of the flow path), and pumping off the boundary layer at the electrodes and preventing lithium condensation on the channel walls. Because of the small magnetic field required, construction of the magnet system will clearly not present substantial technical difficulties associated with its size.The most important physical questions as well as a number of technological questions characteristic of this problem may be investigated on a fairly simple model MHD generator with an output power level of 300–500 MW, a pulse duration of 10–20 msec, and a lithium plasma source.Translated from Atomnaya Énergiya, Vol. 39, No. 6, pp. 387–391, December, 1975.     

A direct current glow discharge plasma source for inner surface modification of metallic tube

A dc glow discharge plasma source was developed for inner surface modification of metallic tubes with an inner diameter of 10 mm. A tungsten wire of 30 μm thick was stretched inside the tube to form coaxial electrodes. DC glow discharge plasma was generated inside the tube by applying a negative high dc voltage to the tube. It was found that the length of the cylindrical plasma bulk depends linearly on the applied voltage. The electron excitation temperature of Ar plasma was measured as 12830 ± 550 K by optical emission spectroscopy method. As a preliminary application, diamond-like carbon (DLC) films were deposited onto the inner surface of stainless steel tube of 100 mm in length and 10 mm in inner diameter by using CH₄/Ar mixture with 40% CH₄ at 40 Pa pressure. The chemical structure of the DLC film deposited on the substrate was analyzed by Raman spectroscopy. The integrated intensity ratio (I_D:I_G) was obtained as 1.62 from the Raman spectra. The thickness of the DLC film deposited on the substrate was estimated as 1.5 μm by scanning electron microscopy (SEM) observation.     

Further insight into mechanisms of solid-state interactions in UMo/Al system

In this paper, the solid-state interactions between metastable γ-UMo alloys (containing 5, 7 and 10 wt%Mo) and Al, at temperatures ranging from 440 to 600 °C and for ageing times up to 10 h, are studied using the diffusion couple technique and nuclear fuel plate annealing. The reaction product consists of three main zones, two of them presenting a periodic layered morphology. The growth kinetics is limited by solid-state diffusion and Al is the most mobile species. Both growth kinetics and its global energy of activation are similar to that found for the U/Al binary system. The diffusion path is determined and phase equilibrium relations are deduced for the Mo-poor part of the U-Mo-Al metastable ternary phase diagram.     

Strong Dependency of Ion Acceleration on Ion Beam Divergency in Magnetized Collisionless Plasma Sheath

The ion acceleration inside the collisionless plasma sheath is investigated at the presence of external magnetic field. By using the fluid model, the number and momentum equations of the ions and the Boltzmann and Poisson equations are solved numerically in the case that the ion beam has a small divergency at the plasma sheath boundary. It is shown that the kinetic energy of the ions has a strong dependency to the magnitude of divergency when the magnetic field has a small component parallel to the sheath boundary.     

Numerical Modeling of a Magnetic Flux Compression Experiment

A possible plasma target for Magnetized Target Fusion (MTF) is a stable diffuse z-pinch in a toroidal cavity, like that in MAGO experiments. To examine key phenomena of such MTF systems, a magnetic flux compression experiment with this geometry is under design. The experiment is modeled with 3 codes: a slug model, the 1D Lagrangian RAVEN code, and the 1D or 2D Eulerian Magneto-Hydro-Radiative-Dynamics-Research (MHRDR) MHD simulation. Even without injection of plasma, high-Z wall plasma is generated by eddy-current Ohmic heating from MG fields. A significant fraction of the available liner kinetic energy goes into Ohmic heating and compression of liner and central-core material. Despite these losses, efficiency of liner compression, expressed as compressed magnetic energy relative to liner kinetic energy, can be close to 50%. With initial fluctuations (1%) imposed on the liner and central conductor density, 2D modeling manifests liner intrusions, caused by the m = 0 Rayleigh-Taylor instability during liner deceleration, and central conductor distortions, caused by the m = 0 curvature-driven MHD instability. At many locations, these modes reduce the gap between the liner and the central core by about a factor of two, to of order 1 mm, at the time of peak magnetic field.     

Study of a new cusp field for an 18 GHz ECR ion source

A feasibility study was performed to generate new sufficient mirror cusp magnetic field (CMF) by using the coils of the existing room temperature traditional 18 GHz electron cyclotron resonance ion source (ECRIS) at RIKEN. The CMF configuration was chosen because it contains plasma superbly and no multipole magnet is needed to make the contained plasma quiescent with no magneto-hydrodynamic (MHD) instability and to make the system cost-effective. The least magnetic field, 13 kG is achieved at the interior wall of the plasma chamber including the point cusps (PC) on the central axis and the ring cusp (RC) on the mid-plane. The mirror ratio calculation and electron simulation were done in the computed CMF. It was found to contain the electrons for longer time than in traditional field. It is proposed that a powerful CMF ECRIS can be constructed, which is capable of producing intense highly charged ion (HCI) beam for light and heavy elements.     

A Compact Torus Fusion Reactor Utilizing a Continuously Generated String of CT’s. The CT String Reactor, CTSR

A fusion reactor is described in which a moving string of mutually repelling compact toruses (alternating helicity, unidirectional Btheta) is generated by repetitive injection using a magnetized coaxial gun driven by continuous gun current with alternating poloidal field. An injected CT relaxes to a minimum magnetic energy equilibrium, moves into a compression cone, and enters a conducting cylinder where the plasma is heated to fusion-producing temperature. The CT then passes into a blanketed region where fusion energy is produced and, on emergence from the fusion region, the CT undergoes controlled expansion in an exit cone where an alternating poloidal field opens the flux surfaces to directly recover the CT magnetic energy as current which is returned to the formation gun. The CT String Reactor (CTSTR) reactor satisfies all the necessary MHD stability requirements and is based on extrapolation of experimentally achieved formation, stability, and plasma confinement. It is supported by extensive 2D, MHD calculations. CTSTR employs minimal external fields supplied by normal conductors, and can produce high fusion power density with uniform wall loading. The geometric simplicity of CTSTR acts to minimize initial and maintenance costs, including periodic replacement of the reactor first wall. Charles W. Hartman—LLNL retired; John Thomas—Privately employed.     

MHD Equilibrium with Reversed Current Density and Magnetic Islands Revisited:the Vacuum Vector Potential Calculus

The solution of Grad-Shafranov equation determines the stationary behavior of fusion plasma inside a tokamak.To solve the equation it is necessary to know the toroidal current density profile.Recent works show that it is possible to determine a magnetohydrodynamic(MHD)equilibrium with reversed current density(RCD)profiles that presents magnetic islands.In this work we show analytical MHD equilibrium with a RCD profile and analyze the structure of the vacuum vector potential associated with these equilibria using the virtual casing principle.     

Investigation of radial heat conduction with 1D self-consistent model in helicon plasmas

A 1D radially self-consistent model in helicon plasmas has been established to investigate the influence of radial heat conduction on plasma transport and wave propagation.Two kinds of 1D radial fluid models,with and without considering heat conduction,have been developed to couple the 1D plasma-wave interaction model,and self-consistent solutions have been obtained.It is concluded that in the low magnetic field range the radial heat conduction plays a moderate role in the transport of helicon p...     

Quasi-static magnetic compression of field-reversed configuration plasma: amended scalings and limits from two-dimensional MHD equilibrium

In this work, several key scaling laws of the quasi-static magnetic compression of field reversed configuration(FRC) plasma(Spencer et al 1983 Phys. Fluids 26 1564) are amended from a series of two-dimensional FRC MHD equilibriums numerically obtained using the Grad–Shafranov equation solver NIMEQ. Based on the new scaling for the elongation and the magnetic fields at the separatrix and the wall, the empirically stable limits for the compression ratio, the fusion gain, and the neutron yield are ...     

Investigation of the fast magnetosonic wave excited by the Alfvén wave phase mixing by using the Hall–MHD model in inhomogeneous plasma

The inhomogeneity is introduced by a nonzero density gradient which separates the plasma into two different regions where plasma density are constant. The Alfvén waves, the phase mixing and the fast magnetosonic wave are excited by the boundary condition in inhomogeneous magnetized plasma. By using the Hall–magnetohydrodynamics(MHD) model, it is found that there are Alfvén waves in the homogeneous regions, while the phase mixing appears in the inhomogeneous region. The interesting result is that a fast magnetosonic wave is excited in a different direction which has a nonzero angle between the wave propagation direction and the direction of the background magnetic field. The dependence of the propagation direction of the excited fast magnetosonic wave and its strength of the magnetic field on the plasma parameters are given numerically. The results show that increasing both the driving frequency and the ratio of magnetic pressure to thermal pressure will increase the acceleration of the electrons. The electron acceleration also depends on the inhomogeneity parameters.     

Ab initio approach to the effect of Fe on the diffusion in hcp Zr II: The energy barriers

Using density functional theory calculations together with the Monomer method for the search of saddle points (combined for the first time with an ab initio algorithm), we obtain the vacancy formation energies and the migration barriers for α-Zr self-diffusion and for the diffusion of interstitial impurities, including the ultra-fast diffuser Fe. Good agreement with measured diffusion coefficients is obtained, as a much lower energy barrier for the ultra-fast diffuser is found. We also suggest a possible mechanism for the increase in self-diffusion due to the Fe impurity, always present in the experimental samples.