Effect of three-dimensional traveling wave magnetic field on plasma sheath density

When the vehicle travels at a hypersonic speed or during re-entry, the surface is covered by a plasma sheath. Plasma sheath can impede electromagnetic wave propagation, causing vehicle radio signals to be attenuated or even interrupted, which is communication blackout. The traveling magnetic field is a kind of magnetic field that can mitigate the communication blackout by adjusting the density of the plasma sheath. In this work, a three-dimensional traveling magnetic field generation model and a three-dimensional plasma density distribution model are established for the problem that the one-dimensional traveling magnetic field cannot accurately describe the plasma density distribution in space. The mechanism of the interaction between the traveling magnetic field and the plasma is investigated to obtain the plasma density distribution in space. The results show that applying a traveling magnetic field can generate a density reduction region of 50 x 100 mm at the rear of the vehicle, resulting in a maximum decrease of 71% in plasma density in the region and providing continuous communication time. Meanwhile, the effects of initial density, collision frequency, traveling velocity and current magnitude on the plasma density distribution are investigated. The results show that with the increase of the initial density, the ability to regulate the plasma density is improved. However, due to the large density base, the adjusted plasma density is still higher than the plasma density of the low-density case. The increase of the collision frequency can significantly reduce the regulation effect. Increasing the traveling velocity and current can enhance the density-adjusting effect. However, further increasing the traveling velocity to above 800 m/s does not yield a more significant adjustment effect. Based on the data from the RAM-C flight test, the proposed model is used to study the effects of current magnitude and traveling velocity on the electromagnetic wave attenuation during aircraft reentry. The mitigation effect of the traveling magnetic field on electromagnetic wave attenuation is also compared with the effect of applying a static magnetic field. The results show that the applied traveling magnetic field can reduce the electromagnetic wave attenuation of the vehicle to below 30 dB in the X-band at an altitude of 30.48km, as well as in the L-, S-, C- and X-bands at other altitudes. The comparison between traveling magnetic field and static magnetic field demonstrates that the traveling magnetic field significantly outperforms the static magnetic field in mitigating electromagnetic wave attenuation.