One of the key factors for solving the problems of re-entry communication interruption is electromagnetic (EM) wave transmission characteristics in a plasma. Theoretical and experimental studies were carried out on specific transmission characteristics for different plasma sheath characteristic under thin sheath condition in re-entry state. The paper presents systematic studies on the variations of wave attenuation characteristics versus plasma sheath thickness L, collision frequency ν, electron density n e and wave working frequency f in a φ 800 mm high temperature shock tube. In experiments, L is set to 4 cm and 38 cm. ν is 2 GHz and 15 GHz. n e is from 1×10 10 cm −3to 1×10 13 cm −3 , and f is set to 2, 5, 10, 14.6 GHz, respectively. Meanwhile, Wentzel-Kramers-Brillouin (WKB) and finite-difference time-domain (FDTD) methods are adopted to carry out theoretical simulation for comparison with experimental results. It is found that when L is much larger than EM wavelength λ (thick sheath) and ν is large, the theoretical result is in good agreement with experimental one, when sheath thickness L is much larger than λ, while ν is relatively small, two theoretical results are obviously different from the experimental ones. It means that the existing theoretical model can not fully describe the contribution of ν. Furthermore, when L and λ are of the same order of magnitude (thin sheath), the experimental result is much smaller than the theoretical values, which indicates that the current model can not properly describe the thin sheath effect on EM attenuation characteristics.
Alkali metal DC arc discharge has the characteristics of easy ionization, low power consumption, high plasma temperature and ionization degree, etc, which can be applied in aerospace vehicles in various ways. In this paper, we calculate the physical property parameters of lithium vapor, one of the major alkali metals, and analyze the discharge characteristics of lithium plasma with the magnetohydrodynamic (MHD) model. The discharge effects between constant current and voltage sources are also compared. It is shown that the lithium plasma of DC arc discharge has relatively high temperature and current density. The peak temperature can reach tens of thousands of K, and the current density reaches 6×10 7 A m −2 . Under the same rated power, the plasma parameters of the constant voltage source discharge are much higher than those of the constant current source discharge, which can be used as the preferred discharge mode for aerospace applications.
Abstract-In this paper, the collisional absorption mechanism of electromagnetic-wave in plasma for DC discharge type is studied with numerical method. The computation model of the electromagnetic-wave collisional absorption in the DC discharge plasma is founded. The FDTD method is presented for simulating the collisional absorption of electromagnetic-wave energy in the one-dimensional inhomogeneous plasma by DC discharge generator. The emulational results illustrate that the inhomogeneous plasma electron density which is produced by DC discharge around the opening space could be approximate to 1014-1015cm-3, and the plasma can absorb the energy of electromagnetic-wave in the wide bandwidth by collisional absorption.
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