Microwave measurements on a well-collimated dusty plasma sheet for communications blackout applications

Summary form only given. Vehicles traveling at hypersonic velocities within the Earth's atmosphere, such as spacecraft during reentry and weapons systems, are enveloped by a dense plasma layer. This plasma layer reflects and significantly attenuates GPS and S-band signals for vehicle navigation, telemetry, and voice communications, resulting in radio blackout. In these studies, a linear hollow cathode produces an electron beam that is accelerated into a low pressure (50 to 150 mTorr) background of Argon gas, producing an electron beam discharge. A relatively constant 170 Gauss axial magnetic field is produced by two electromagnet coils arranged in a Helmholtz configuration. This results in a well-collimated electron beam, producing a 2-dimensional Argon plasma discharge in a sheet configuration. This discharge sheet is approximately 40 cm long by 30 cm wide by 1 cm thick, and can produce electron densities as high as 1012 cm-3. The plasma sheet is intended to mimic the intense plasma layer produced and experienced by vehicles traveling at hypersonic velocities. The electron beam is accelerated vertically towards a grounded beam dump electrode. This electrode is modified to include an array of six piezo buzzers modified and filled with alumina powder. When supplied with a modest voltage, the piezoelectric shakers uniformly drop dust particles into the plasma sheet discharge directly below at a constant rate, creating a dusty plasma. A transmitting microwave horn is oriented normal to the dense plasma sheet while the receiving horn is mounted on a stage that can be rotated up to 180 degrees azimuthally. Microwave cutoff, transmission, reflection, and scattering measurements of the plasma sheet are made in the S-band and X-band range. These measurements are relevant for applications related to communications blackout and over-the-horizon communications.