Effect Of Magnetic Field Topology Research Articles

Electron confinement investigation in low beta magnetic polywell configurations

This study uses numerical simulations to investigate the effects of magnetic field topology resulting from various polywell fusion setup configurations, including the cube configuration (6 coils), dodecahedron configuration (12 coils), double-layer configuration (14 coils) and disco configuration (26 coils). The results suggest that increased number of magnetic coils and magnitude of magnetic flux density through increased coil current leads to a longer electron confinement time. This is shown by the increased magnetic flux density and magnetic well width with increasing number of coils. In addition, each configuration is investigated to predict the capacity of electron confinement. Numerical electron injections are applied to each magnetic field topology to determine the decay behavior of electron numbers, from which the electron confinement time is calculated.

Impact of Ordered and Disordered Magnetic Fields on Multiwavelength Emission of Blazars

Abstract We present a detailed analysis of the effects of magnetic field topology on the spectral energy distribution (SED) and spectral variability patterns (SVPs) of blazars. In order to study these effects, we have extended our time-dependent leptonic jet model (in the internal shock scenario) to include the dependence of the synchrotron emissivity on the angle between the photon direction and the magnetic field in the plasma frame. We have explored the effects of different magnetic field geometries, such as parallel, perpendicular, oblique, toroidal, and helical, on the simulated SEDs and SVPs of a generic blazar for both purely ordered and disordered components of fields. These considerations provide either upper or lower limits to the impact on blazar emission, depending on the fraction of a disordered component present and the viewing angle. The results of our work point out some of the signatures that the orientations can leave on the SEDs and SVPs of a blazar. For example, in the case of a purely oblique field, if the magnetic field is aligned along the line of sight (in the plasma frame), it results in an annulment of the synchrotron component while keeping the flux level of the high-energy component intact. On the other hand, in the presence of a disordered component, the impact of an oblique field is reduced, and the same effect is not observed.

Effects of magnetic field topology in black hole-neutron star mergers: Long-term simulations

We report long-term simulations of black hole-neutron star binary mergers where the neutron star possesses an asymmetric magnetic field dipole. Focusing on the scenario where the neutron star is tidally disrupted by the black hole, we track the evolution of the binary up to $\approx 100$ms after the merger. We uncover more than one episode of thermally driven winds being launched along a funnel wall in all these cases beginning from $\approx 25$ms after the merger. On the other hand, we are unable to conclude presently whether the amount of ejected mass increases with the \it{degree} of asymmetry. A large-scale magnetic field configuration in the poloidal direction is formed along the funnel wall accompanied by the generation of a large Poynting flux. The magnetic field in the accretion disk around the black hole remnant is amplified by the nonaxisymmetric magnetorotational instability (MRI). The MRI growth is estimated to be in the ideal magnetohydrodynamics (MHD) regime and thus would be free from significant effects induced by potential neutrino radiation. However, the asymmetry in the magnetic field leads to increased turbulence, which causes the vertical magnetic field in the accretion disk to grow largely in a nonlinear manner.

The effects of magnetic field topology on secondary neutron spectra in Magnetized Liner Inertial Fusion

The Magnetized Liner Inertial Fusion (MagLIF) concept involves the compression of a magnetized fuel such that the stagnated fuel contains a magnetic field that can suppress heat flow losses and confine α particles. Magnetic confinement of α particles reduces the fuel ρR required for ignition. Recent work [1,2] has demonstrated that the magnitude of the magnetic field in deuterium fuel can be inferred from the yields and spectra of secondary DT neutrons. In this work we investigate the potential for using the shape of the secondary neutron spectra to diagnose the magnetic field topology in the stagnated fuel. Three different field topologies that could possibly occur in MagLIF experiments are studied: (1) a cylindrical fuel column containing axial and azimuthal magnetic field components, (2) a fuel column which is pinched at the ends to form a magnetic mirror and (3) a fuel column that has a helical tube shape with magnetic field lines following the helical path of the tube’s axis. Each topology is motivated by observations from experimental or simulated MagLIF data. For each topology we use a multi-physics model to investigate the shapes of the secondary neutron spectra emitted from a steady-state stagnated fuel column. It is found that the azimuthal and helical topologies are more suitable than the mirror topology for reproducing an asymmetry in the axial spectra that was observed in experiments. Gorgon MHD simulations of the MagLIF implosion in 1D are also carried out. These show that sufficient azimuthal magnetic field can penetrate from the liner into the fuel to qualitatively reproduce the observed spectral asymmetry.

Effect of magnetic field topology on quasi-stationary equilibrium, fluctuations, and flows in a simple toroidal device

In a simple toroidal device, the plasma profiles and properties depend on toroidal magnetic field topology. For example, the toroidal connection length crucially controls the adiabatic or non-adiabatic nature of electron dynamics, which in turn governs the nature of instabilities, fluctuations, and transport, the latter of which governs the plasma mean profiles. We present the results of extensive experiments in a simple toroidal device obtained by controlling the mean parallel connection length L¯c, by application of external vertical component of magnetic field Bv, where Bv≤2% of toroidal magnetic field BT. Interestingly, for nearly closed field lines, which are characterized by large values of L¯c, it is found that flute like coherent modes are observed to be dominant and is accompanied by large poloidal flows. For small values of L¯c, the mean density on the high field side is seen to increase and the net poloidal flow reduces while a turbulent broad band in fluctuation spectrum is observed. Upon a gradual variation of L¯c from large to small values, continuous changes in mean plasma potential and density profiles, fluctuation, and poloidal flows demonstrate that in a simple toroidal device there exists a strong relationship between Lc, flows, and fluctuations. The net flow measured is found independent of the direction of Bv, but an asymmetry in the magnitude of the flow is found. The observed imbalance between the mean flow, fluctuation driven flow, and net flow is also discussed.

Ion extraction experiment for electron cyclotron resonance ion source with different magnetic topology

Electron cyclotron resonance ion source (ECRIS) for space propulsion requires to be compact and efficient. In this work, ECRIS, which generates magnetic field through permanent magnets, is compact and heats electrons by microwave in magnetic field to induce ionization collision and produce plasma. In ECRIS, magnetic field is crucial in gas discharge, plasma confinement and transport. Due to the complex interaction among the processes, including plasma generation, wave transmission and ion extraction, the effects of magnetic field on the performance of ECRIS are complex. In this paper, the effects of magnetic field topology on the performance of the ECRIS are studied experimentally. Argon is discharged by microwaves in four types of ion sources, different in the magnet positions and the ion beam extracted. The gas flow rate varies from 30 to 210 g/s, the microwave power from 10 to 20 W and the extracting voltage form 500 to 1500 V. The properties of the ion sources are analyzed by comparing their extracted ion beams, propellant utilization efficiency, discharge loss and stability. Results show that the maximum ion beam, the highest gas utilization efficiency and the minimum discharge loss are respectively 160 mA, 60%, and 120 WA-1. Each ion source presents more than one mode, determined by the microwave power and the gas flow rate, and affected by the extracting voltage. The microwave power and the gas flow rate at which the ion source mode changes relative to the position of the magnets. Finally, the influences of magnetic topology on the performance of the ion source are summarized and analyzed. It is concluded that inside this kind of ECRIS, the magnetic field featured by a wide electron cyclotron resonance (ECR) zone, and the narrow gap between the ECR zone and the screen grid will increase the extracted ion beam at the same level of the input power and the gas supply. But it is difficult to achieve high gas utilization efficiency in the ion source with such a structure. By keeping the ECR zone close to the power entrance, the gas inlet will significantly decrease the threshold for the power and gas consumption to sustain the high current mode. But the discharge loss in the ion source of such a structure is huge. Elaborate considerations should be taken to balance the magnitude of the extracted ion beam and the efficiency. These results may improve the understanding of the working process of this type of ECRIS and help the design processes.

Experimental and theoretical study on effects of magnetic field topology on near wall conductivity in a Hall thruster

An experiment has been made to investigate the effect of curved magnetic field topology on near wall conductivity in the ion acceleration region of Hall thrusters. The experimental results show that the electron current due to near wall conductivity is of the minimum in the case of focused topology and increases in the cases of both less-focus and over-focus topologies. This finding cannot be explained properly by the magnetic mirror effect, which is the one and only reported effect related to the magnetic field curvature so far. Based on the analysis of interaction between the plasma and the wall, a new physical effect is proposed. The difference of magnetic field topology causes different electric potential distribution, leads to different ion flux to the wall, results in the change of sheath property and secondary electron emission, and finally affects the electron current due to near wall conductivity. This effect is further justified by the agreement between the experiment and simulation which is performed with a particle-in-cell model. Therefore, we conclude that the ion flow injection is a significant effect to near wall conductivity in the scope of curved magnetic field topology besides the magnetic mirror effect. Moreover, we find that the focus topology of magnetic field is favorable to obtain a high thruster performance from both the ion acceleration aspect and the electron conduction aspect and so is useful practically for thruster optimization.