Electron beam emission from the EXOS-B (JIKIKEN) satellite as a powerful diagnostic tool in the magnetosphere

The use of a satellite-borne low-power electron beam to measure plasma density and magnetic-field strength in the magnetosphere is demonstrated using data from the Japanese EXOS-B satellite. The EXOS-B electron gun is a Pierce-type axisymmetric parallel-beam gun with Wehnert electrode; 5-mm exit diameter; divergence 0.3 rad; 16-kHz 2.9-W power supply; beam current adjustable to 250, 500, 750, or 1000 microA; and beam voltage adjustable to -100, -125, -150, or -200 V. Receiver equipment includes a 110-m dipole antenna and a frequency analyzer with range 10 kHz to 3 MHz, bandwidth 5 kHz, and period 2 or 8 sec. Sample spectra and density profiles are shown, and it is found that plasma densities to the order of 10/cu cm can be measured.