Experimental Two-Beam Excitation of Electron Oscillations in a Plasma Without Sheaths

Coherent standing waves of longitudinal electron oscilla tions were excited in a plasma by two independent oppositely directed electron beams at 65 ev, having no electrode sheaths. Strorg sinusoidal standing waves, with two loops between electrodes, were found at 550 Mc/sec only when both beams and the plasma were present. Taking the distance between the electrodes as a wavelength, the phase velocity was 1.10 x 10/sup 9/ cm/sec; the electron velocity of either beam was 0.48 x 10/sup 9/ cm/sec. A single-loop standing wave was established with a beam energy of 74 ev. With either one or two loops, the standing wave amplitude fell gradually to zero when the voltage was increased or decreased approximately 3 volts from the stated value. An oscillation frequency spectrum and the test apparatus arrangements are illustrated. (B.O.G.)