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In this paper, the collisionless electrostatic instability of the entropy mode is investigated linearly in multi-component plasmas confined by a dipole magnetic field, which commonly exists in space environments, as well as laboratory plasmas, such as Collisionless Terrella eXperiment, Levitated Dipole eXperiment, and Dipole Research EXperiment. We focus on characteristics of the entropy mode driven by the plasma density or/and the temperature gradient at low plasma beta (=8πP0/B02). The theoretical analysis of this work agrees with the calculated results qualitatively. It is indicated that the peak growth rate of the instability is in the regime of k⊥ρi ∼ 1, and the entropy mode tends to be more stable as the percentage of the heavy ion increases. For multi-component plasmas, each component has the entropy mode feature of its own, instead of simply averaging all the components. While for the electron with an isotropic temperature, the use of weighted harmonic average can be a good approximation for simplification. [ABSTRACT FROM AUTHOR]

Entropy modes are typical instabilities particularly seen in dipole field confined plasmas. In this paper, linear gyrokinetic calculations, together with the integral dispersion relation method, are applied to study the electrostatic entropy mode in such plasmas with an anisotropic temperature. The numerical approach is verified for certain typical conditions with previous studies. We then further focus on the anisotropic temperature effect on the entropy mode. Basic characteristics of the entropy mode are obtained with the effect. The results show that the entropy mode has a peak growth rate at kρi ∼ 1, and the mode is shifted from the ion to the electron diamagnetic regimes at small k⊥ρi. This work can be applied for various dipole magnetic field confined plasmas as well as certain other configurations, such as Z-pinch and field reversed configurations. [ABSTRACT FROM AUTHOR]

Chorus waves are widely investigated in space physics due to their significant role played in the radiation belts. Multiple structures of chorus frequency chirping elements, such as rising-tone structure, falling-tone structure, and hook-like structure, are observed in both space plasmas and the ground simulation experiments. In this paper, the numerical simulation on the generation of descending elements of chorus waves with parameters of a launching device, Dipole Research EXperiment, is conducted by a hybrid code named DAWN. The descending element of chorus waves is self-consistently generated without additional requirements except for a hot electron component as the free energy source. A case of ascending element under the magnetosphere parameters is also carried out to verify our simulations. Phase space distributions of electrons for the two chirping structures are analyzed, and the simulation results are consistent with previous theoretical predictions. It is obtained from the simulation results that the ascending element of chorus is observed together with an electron phase space hole (a depleted distribution function), while the descending elemet is observed together with an electron phase space clump. [ABSTRACT FROM AUTHOR]

Electron beam-generated plasmas (EBPs) have been used to modify the surface properties. In certain applications, EBPs are transversely confined and their properties are of value to the treatment. In this paper, the characteristics of an electron beam-generated argon plasma, confined within a narrow gap, are investigated using a two-dimensional particle-in-cell simulation. The employed particle-in-cell/Monte Carlo collision model accounts for the electron and ion kinetics, as well as collisions between electrons and the background gas, including the elastic scattering, excitation, and impact ionization. Our simulations reveal a strong correlation between the plasma density and the beam density within the plasma bulk. The excitation of obliquely growing waves is observed, which is found to have a significant impact on the transport of beam electrons, thereby leading to the non-uniformities of plasma density and electron temperature. Specifically, the obliquely growing waves increase the local plasma density while reducing the electron temperature. These contrasting effects compensate for each other, and therefore, to some extent, smooth out the distributions of ion flux and energy flux. We further examine the variations of plasma parameters with respect to the beam current density, beam energy, and gas pressure. Increasing the beam current density or decreasing the beam energy results in higher plasma density and electron temperature, while increasing pressure leads to a higher plasma density but electron temperature scarcely changes. Based on the simulation results, we propose an approach to achieve independent control of the ion flux and energy flux by adjusting beam current density, beam energy, and pressure. [ABSTRACT FROM AUTHOR]

A scientific research device for geospace physics, the Space Plasma Environment Research Facility (SPERF), is going to be in operation this year at the Harbin Institute of Technology, China. One of its laboratory simulation platforms, the Asymmetric Reconnection EXperiment (AREX), is designed to investigate the asymmetric magnetic reconnection relevant to the process in the dayside magnetopause of the Earth. As a ground-based experimental platform, AREX emphasizes three-dimensional (3D) asymmetric driving features with topological similarity relevant to dayside reconnection. Thus, in this paper, we focus on topological analysis based on numerical simulation of AREX reconnection processes. 3D topological features in various scenarios relevant to magnetopause reconnection in different interplanetary magnetic field (IMF) conditions are investigated by adjusting setup parameters of plasma sources and magnetic coils. The simulation results reveal that the plasma distribution of asymmetric reconnection in SPERF-AREX is analogous to that at the magnetopause. Various types of the 3D magnetic topology relevant to typical IMF conditions, including the X-line and the A–B null chain structures, are, respectively, identified and analyzed in detail. [ABSTRACT FROM AUTHOR]