Electron beam measurements for a laboratory simulation of auroral kilometric radiation

Efficient (similar to 1%) electron cyclotron radio emissions are produced in the X-mode from regions of locally depleted plasma in the Earth's polar magnetosphere. These emissions are commonly referred to as auroral kilometric radiation. Two populations of electrons exist with rotational kinetic energy to contribute to this effect, the downward propagating auroral electron flux which acquires transverse momentum due to conservation of the magnetic moment as it experiences an increasing magnetic field and the mirrored component of this flux. This paper demonstrates the production of an electron beam having a controlled velocity spread for use in an experiment to investigate the available free energy in the earthbound electron flux. The experiment was scaled to microwave frequencies and used an electron gun to inject an electron beam into a controlled region of increasing magnetic field produced by a set of solenoids reproducing the magnetospheric situation. Results are presented of the measurements of diode voltage, beam current as a function of magnetic mirror ratio and estimates of the line density versus electron pitch angle consistent with the formation of a horseshoe velocity distribution and demonstrating control of the electron distribution in velocity space.