Experimental apparatus for investigating the propagation characteristics of the low-frequency electromagnetic waves in hypersonic plasma fluid generated by shock tube.

The shock tube generates a near real hypersonic plasma sheath environment with high temperature and high pressure for investigating the propagation characteristics of the electromagnetic (EM) waves in a hypersonic plasma fluid. With existing methods, it is difficult to measure the propagation characteristics from the transmitted component of low-frequency (LF) EM waves due to large-size LF focusing antennas and LF shielding structure. In this paper, a novel experimental apparatus is proposed to measure the propagation characteristics of the LF EM waves in a shock-tube-generated hypersonic plasma fluid. The tested plasma is utilized as a dynamic fluid EM shield of a receiver during the experiment. This individual receiver is placed in the center of the experimental segment tube of the shock tube so that it is enveloped completely by the hypersonic plasma fluid during the shock, thereby only allows the transmitted component of the LF EM waves to reach the receiver. The proposed method guarantees good measurement accuracy without requiring large LF focusing antennas, and the complex LF shielding structure extends to the shock tube. Both experiments and simulations were performed to evaluate its performance. The results indicated that the propagation characteristics of the transmitted magnetic field component meet that of the numerical simulations faithfully, where the shock wave velocity reached approximately 5 km/s, the plasma layer thickness was 80 mm, the electron density was 10-10/cm, and the collision frequency was approximately 36 GHz. The proposed experimental apparatus is also suitable in studying the EM wave propagation, testing communication system performances, and testing the properties of transmitting and receiving antennas in the hypersonic plasma fluid.