Double-Frequency-Shift Acousto-Optic Modulator with Controllable Pulse Pair Frequency Difference

A scheme for controlling the frequency difference of output pulse pair with double frequency shift loops is proposed. The frequency shift system includes two loop elements of 20 and 200 MHz. The first one carries out a single selective positive frequency shift of 1–20 MHz, and the second one can satisfy a single fixed positive frequency shift of 200 MHz. The reverse cascade technology of two acousto-optic crystals is introduced to solve the limitation of the small frequency shift of crystal size. A multichannel synchronization signal completes the time domain control of each acousto-optic modulator. Finally, the frequency shift difference of the output pulse pair ranges of 0–2 GHz, and the frequency shift accuracy is 5 MHz.

TCV-like event induced by positive-negative pulse pair of solar wind dynamic pressure

<p>Both simulations and observations had shown that step function-like increase/decrease of solar wind dynamic pressure pulse would excite flow vortex pairs in the dawn and dusk high latitude ionosphere simultaneously. However, some plasma structures, hot flow anomaly, sheath jets etc. existing in the solar wind or magnetosheath are often accompanied with spike-like changes of the dynamic pressure. Whether they can drive the ionospheric vortices or not is still unclear. In this work we report a traveling convection vortex like (TCV-like) event that was induced by a positive-negative pulse pair of dynamic pressure(△p/p~1) accompanying a large scale (~9min) magnetic hole in the solar wind. It is found that following the magnetic hole, two traveling convection vortices first in anticlockwise then in clockwise rotation were detected by geomagnetic stations located along the 10:30MLT meridian. Meanwhile, another pair of ionospheric vortices azimuthally seen up to 3 MLT first in clockwise then in anticlockwise rotation were appeared in the afternoon sector (~14MLT) centered at ~75MLAT with a trend of poleward moving. The duskside vortices were also confirmed by SuperDARN radar data. The processes following magnetosphere struck by a positive-negative pulse pair were simulated and it found that two pairs of flow vortices in the dawn and dusk magnetosphere may provide the field-aligned currents(FACs) required for the flow/current vortices observed in ionosphere. This work provides a way to understand how the momentum and energy injects to the ionosphere under spike-like dynamic pressures imposing on the magnetosphere.</p>