A 200-eV electron beam is incident on an electrode in a laboratory plasma. The emission of secondary electrons produces a region of negative differential resistance in the current-voltage characteristic of the electrode. Spontaneous dynatron oscillations are driven by the negative differential resistance when a resonant circuit is placed in series with the electrode. The instability is driven by the beam energy, produces large amplitudes comparable to the beam voltage, modulates beam and plasma parameters, and excites plasma eigenmodes such as ion acoustic waves. [S0031-9007(98)
In a large laboratory plasma, reconnection of three-dimensional (3-D) magnetic fields is studied in the parameter regime of electron magnetohydrodynamics. A reversed magnetic field topology with two 3-D null points and a two-dimensional (2-D) null line is established, and its free relaxation is studied experimentally. Major new findings include the absence of tilting instabilities in an unbounded plasma, relaxation times fast compared to classical diffusion times, dominance of field line annihilation at the 2-D current sheet versus reconnection at 3-D null points, conversion of magnetic energy into electron thermal energy, and excitation of various microinstabilities. This first of four companion papers focuses on the magnetic field topology and dynamics.
In a large laboratory plasma reconnection of three-dimensional (3-D) magnetic fields is studied in the parameter regime of electron magnetohydrodynamics (EMHD). A reversed-field topology with two 3-D null points and a two-dimensional (2-D) null line is established, and its free relaxation is studied experimentally. Major new findings include the absence of tilting instabilities in an unbounded plasma, relaxation times that are fast compared to classical diffusion times, dominance of field line annihilation at the 2-D current sheet versus reconnection at 3-D null points, conversion of magnetic energy into electron thermal energy, and excitation of various microinstabilities. The experiment implies that EMHD processes near absolute magnetic null points must be considered in the multiscale physics of magnetic reconnection.
Magnetic vortices in the parameter regime of electron magnetohydrodynamics are studied in a large laboratory plasma. The vortices consist of magnetic field perturbations, which propagate in the whistler mode along a uniform dc magnetic field. The magnetic self-helicity of the spheromak-like field perturbations depends on the direction of propagation. Vortices with opposite toroidal or poloidal fields are launched from two antennas and propagated through each other. The vortices collide and propagate through one another without an exchange of momentum, energy, and helicity. The absence of nonlinear interactions is explained by the force-free fields of electron magnetohydrodynamic (EMHD) vortices.
In a large laboratory plasma, reconnection of three-dimensional (3D) magnetic fields is studied in the parameter regime of electron magnetohydrodynamics (EMHD). The field topologies are spheromak-like with twodimensional null lines and three-dimensional spiral null points. The relaxation of an initial vortex field by spontaneous reconnection is studied in the absence of boundary effects. Reconnection rates and energy conversion from fields to particles are measured. The frozen-in condition appears to be destroyed by viscous effects rather than inertia or collision. Finally, the non-driven merging of two EMHD spheromaks into a long-lived FRC is observed.These basic physics experiments demonstrate that reconnection is an important process in the parameter regime of unmagnetized ions, which is always encountered near absolute magnetic null points.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.