Experimental investigations of electron wave structures in high-current plasma lens

The authors describe experimental investigations the dispersion characteristics of electron oscillations exciting owing to drift instability in a high-current plasma lens. The experiments were carried out using heavy metal ion beams of copper and carbon with energy up to 18 keV, beam current up to 0.5 A, duration 100 μs produced by the MEWA kind ion source. It is shown that under the passing of an ion beam through a plasma lens, noise oscillations of electrostatic potential arise in the midplane of the lens. These noises have a regular structure with stationary amplitude in range of 0.25÷2 MHz depending on ion beam current value. It observed also on their background a path of comparable low-intensity high-frequencies noises in range 20÷50 MHz. They show that the regular structure is waves drift along the azimuth having a clear spatial localization on the essential radius from plasma lens axis. Experimental results are in accordance with theoretical analysis showing an appearance of nonlinear electron vortices structures for these conditions