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The feasibility of harmonic generation in a planar nanoscale unipolar diode, called a self-switching device, is analyzed using a two-dimensional ensemble Monte Carlo method. A suitable channel width is chosen to enable a zero threshold voltage. The current-voltage and capacitance-voltage characteristics both demonstrate strong nonlinearity. It is shown that the noise of the device is below the shot noise level until about 1THz, after which two noise peaks arise. As such, a good signal-to-noise ratio can be achieved for up to six harmonics and beyond 1THz. The physical origins of the noise peaks are discussed.

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The coronal heating region is able to generate mirror mode structures by ion mirror instabilities. Linear magnetic holes are believed to be the remnants of mirror mode structures, thus they are believed to be messengers from the coronal heating region. They can be convected to ∼9 au with the solar wind flow, indicating that a stabilizing mechanism is necessary to make the magnetic holes survive for such a long time. Here, we investigate a magnetic hole with a size of ∼6.7 ρ i in the solar wind based on observations by the Magnetospheric Multiscale mission. The unprecedented high-resolution data enable us to reveal the existence of the ion vortex inside the structure for the first time. Such an ion vortex forms a ring-like current, which is consistent with the magnetic field depression. The self-consistent structure of the magnetic hole contributed by the ion vortex can help to further shed light on the mechanism of the long-term survival of magnetic holes in the astrophysical plasma.

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