Laboratory plasma devices for space physics investigation

In the past decades, laboratory experiments have contributed significantly to the exploration of the fundamental physics of space plasmas. Since 1908, when Birkeland invented the first terrella device, numerous experimental apparatuses have been designed and constructed for space physics investigations, and beneficial achievements have been gained using these laboratory plasma devices. In the present work, we review the initiation, development, and current status of laboratory plasma devices for space physics investigations. The notable experimental apparatuses are categorized and discussed according to the central scientific research topics they are related to, such as space plasma waves and instabilities, magnetic field generation and reconnection, and modeling of the Earth's and planetary space environments. The characteristics of each device, including the plasma configuration, plasma generation, and control method, are highlighted and described in detail. In addition, their contributions to reveal the underlying physics of space observations are also briefly discussed. For the scope of future research, various challenges are discussed, and suggestions are provided for the construction of new and enhanced devices. The objective of this work is to allow space physicists and planetary scientists to enhance their knowledge of the experimental apparatuses and the corresponding experimental techniques, thereby facilitating the combination of spacecraft observation, numerical simulation, and laboratory experiments and consequently promoting the development of space physics.

Spatial measurement in rotating magnetic field plasma acceleration method by using two-dimensional scanning instrument and thrust stand

A two-dimensional scanning probe instrument has been developed to survey spatial plasma characteristics in our electrodeless plasma acceleration schemes. In particular, diagnostics of plasma parameters, e.g., plasma density, temperature, velocity, and excited magnetic field, are essential for elucidating physical phenomena since we have been concentrating on next generation plasma propulsion methods, e.g., Rotating Magnetic Field plasma acceleration method, by characterizing the plasma performance. Moreover, in order to estimate the thrust performance in our experimental scheme, we have also mounted a thrust stand, which has a target type, on this movable instrument, and scanned the axial profile of the thrust performance in the presence of the external magnetic field generated by using permanent magnets, so as to investigate the plasma captured in a stand area, considering the divergent field lines in the downstream region of a generation antenna. In this paper, we will introduce the novel measurement instrument and describe how to measure these parameters.

A Concept of Cross-Ferroic Plasma Turbulence

The variety of scalar and vector fields in laboratory and nature plasmas is formed by plasma turbulence. Drift-wave fluctuations, driven by density gradients in magnetized plasmas, are known to relax the density gradient while they can generate flows. On the other hand, the sheared flow in the direction of magnetic fields causes Kelvin-Helmholtz type instabilities, which mix particle and momentum. These different types of fluctuations coexist in laboratory and nature, so that the multiple mechanisms for structural formation exist in extremely non-equilibrium plasmas. Here we report the discovery of a new order in plasma turbulence, in which chained structure formation is realized by cross-interaction between inhomogeneities of scalar and vector fields. The concept of cross-ferroic turbulence is developed, and the causal relation in the multiple mechanisms behind structural formation is identified, by measuring the relaxation rate and dissipation power caused by the complex turbulence-driven flux.

Plasma response to a varying degree of stress

We report experimental evidence of a seamless transition between three distinct modes in a magnetized plasma with a transverse sheared flow as the ratio of the ion gyroradius to the shear scale length (a measure of shear magnitude) is varied. This was achieved using a dual plasma configuration in a laboratory experiment, where a sheared flow oriented perpendicular to a background magnetic field is localized at the boundary of the plasmas. This confirms the basic theory that plasma is unstable to transverse velocity shear in a broad frequency and wavelength range. The experiment characterizes the compression or relaxation of boundary layers often generated in a variety of laboratory and space plasma processes.

Electron-ion hybrid instability experiment upgrades to the Auburn Linear Experiment for Instability Studies

The Auburn Linear EXperiment for Instability Studies (ALEXIS) is a laboratory plasma physics experiment used to study spatially inhomogeneous flows in a magnetized cylindrical plasma column that are driven by crossed electric (E) and magnetic (B) fields. ALEXIS was recently upgraded to include a small, secondary plasma source for a new dual source, interpenetrating plasma experiment. Using two plasma sources allows for highly localized electric fields to be made at the boundary of the two plasmas, inducing strong E × B velocity shear in the plasma, which can give rise to a regime of instabilities that have not previously been studied in ALEXIS. The dual plasma configuration makes it possible to have independent control over the velocity shear and the density gradient. This paper discusses the recent addition of the secondary plasma source to ALEXIS, as well as the plasma diagnostics used to measure electric fields and electron densities.

Spontaneous electromagnetic emission from a strongly localized plasma flow

Laboratory observations of electromagnetic ion-cyclotron waves generated by a localized transverse dc electric field are reported. Experiments indicate that these waves result from a strong E×B flow inhomogeneity in a mildly collisional plasma with subcritical magnetic field-aligned current. The wave amplitude scales with the magnitude of the applied radial dc electric field. The electromagnetic signatures become stronger with increasing plasma β, and the radial extent of the power is larger than that of the electrostatic counterpart. Near-Earth space weather implications of the results are discussed.

Multiscale coherent structures and broadband waves due to parallel inhomogeneous flows

Linear theory analysis and particle-in-cell simulations show that a spatial transverse gradient in the ion drift parallel to the magnetic field, dV(di)/dx</=Omega(i), where Omega(i) is the ion cyclotron frequency, can generate a broadband multimode spectrum extending from omega<<Omega(i) to omega>>Omega(i). Nonlinearly, these waves lead to multiscale spatially coherent structures, substantial cross-field transport, ion energization, and phase-space diffusion. Large spikes are formed in the parallel electric field time series. These signatures are similar to the Fast Auroral Snapshot satellite observations in the upward current region.