Laboratory generation of broadband ELF waves by inhomogeneous plasma flow

Abstract

Transversely accelerated ions and the associated heating of the high‐latitude ionosphere have been attributed to broadband extremely low frequency (BBELF) turbulence. Controlled laboratory tests of the hypotheses on the formation mechanism of BBELF waves have involved only a few examples, e.g., current‐driven and shear‐driven instabilities. In this work, electrostatic fluctuations in the ion cyclotron frequency range have been excited by inhomogeneous energy‐density‐driven instability (IEDDI). This was achieved using the interpenetrating plasma method with a much larger electric field scale size LE comparable to the ion gyroradius ρi, which was challenging earlier because of plasma conditions. The peak frequency of the IEDDI spectrum falls as low as ω≈0.3ωci, where ωci is ion cyclotron frequency. This is an interesting result because the previous attempts could not produce such low‐frequency IEDDI, although it was known theoretically to be possible. The observations made by FAST, Freja, and Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites might be explainable in terms of the reported experimental results.

Laboratory Excitation of the Kelvin‐Helmholtz Instability in an Ionospheric‐Like Plasma

“…The cathode plasma,16 cm in diameter, is located in the central part of the vacuum vessel, and the RF plasma is distributed in the outer region. The plasma density and potential between the two plasmas can be independently controlled through a disk‐mesh design (Liu et al, ). A Macor disk is arranged at the region of ME2 to block the central part of the RF plasma.…”

“…These tools, including a Langmuir probe, an electrically floating emissive probe, a two‐dimension Mach probe, and three modified triple probes have been used in the experiment. The characteristics of these probes have been depicted previously (Liu et al, ). In this experiment, the plasma parameter is time variable, and it is difficult to obtain the plasma profile.…”

“…The sheared flow has been frequently observed by satellites and rockets in solar‐terrestrial space plasmas (Ganguli et al, ; Miura, , ; Moore et al, ; Paschmann et al, ; Sundkvist et al, ), and it is widely taken as a dominant source of free energy for the excitation of the electrostatic and electromagnetic instability in a broadband frequency range (Amatucci, ; DuBois, Thomas Jr, et al, ; Ganguli et al, ; Liu et al, ; Liu et al, ; Tejero et al, ). The Kelvin‐Helmholtz instability (KHI) is one of the shear‐driven modes (Peñano & Ganguli, ), and it is frequently observed in the solar corona, solar wind, magnetopause, inner magnetosphere, and ionosphere of the Earth, planets, and comets (Fairfield et al, ; Johnson et al, ; Nykyri & Otto, ; Phan & Paschmann, ; Soler et al, ; Terada et al, ).…”

The Detached Auroras Induced by the Solar Wind Pressure Enhancement in Both Hemispheres From Imaging and In Situ Particle Observations

“…The magnetic field intensity at equatorial plane is reasonably assumed to increase when the magnetosphere is compressed by the solar wind pressure enhancement, as seen from Figure a. As the first adiabatic invariant and the total energy are conserved, the temperature anisotropy can be expected to increase after the magnetosphere compressed by the solar wind dynamic pressure enhancement, resulting in the ion cyclotron instability (Anderson & Hamilton, ; Liu et al, ; Zhou & Tsurutani, ). At the same time the enhanced pressure can be expected to compress the ring current, bringing it closer to the Earth (Wang et al, ), encountering with the cold and dense plasmasphere which lowers the instability threshold (Gary et al, ).…”

A New Perspective for Dipolarization Front Dynamics: Electromagnetic Effects of Velocity Inhomogeneity

“…Specifically, the electron-ion hybrid (EIH) instability is driven by the transverse velocity shear with intermediate scale length ( e < L E < i ), when ions are effectively unmagnetized and electrons have shear corrected velocity distributions (e.g., Ganguli et al, 1988aGanguli et al, , 1988bRomero et al, 1992). The kinetic EIH modes have been verified in a number of space and laboratory experiments and numerical simulations (e.g., Amatucci et al, 1996;DuBois et al, 2014;Liu et al, 2014Liu et al, , 2017Romero & Ganguli, 1993;Scales, Bernhardt, Ganguli, Siefring, & Rodriguez, 1994) and are suggested to be important mechanisms for the generation of broadband electrostatic fluctuations. However, previous EIH studies have been mostly focused on the electrostatic emissions and assumed uniform magnetic field for simplicity (e.g., Romero & Ganguli, 1993;Romero et al, 1992).…”