Science Pictures

Plasma lens

copyright © Onera 2007 - All rights reserved
Experimental assembly for the study of the deviation of an electromagnetic wave by a plasma lens.
Left part: a funnel antenna and a Fresnel lens for the emission and the focusing of the wave.
Right part: the containment chamber of the plasma between the two Helmhotz coils.

This is an original quasi-optical device, designed to divert a beam which is electromagnetic and not light, for example X-band radio waves. No mechanical movement. It’s controlled by varying the properties of a rather special lens – made of plasma – a material state constituted of ions and electrons with very particular properties.

This plasma is obtained from an electrical discharge confined in a chamber filled with gases - helium, neon or xenon - at very low pressure. An almost uniform magnetic field, generated by two Helmholtz coils, structures the plasma and gives it a cylindrical geometry, which is effectively the plasma lens. The density of electrons is at a maximum in the axis of the cylinder and cancels out at the wall of the chamber.

An electromagnetic wave, produced by a funnel antenna and focused by a Fresnel lens, meets this plasma of radially variable electronic density and undergoes a deviation from its propagation axis. The angle of this deviation may be modified by controlling the density of electrons by, for example, changing the pressure of the gases in the chamber, or by modulating the discharge current.

copyright © Onera 2007 - All rights reserved
Deviation of a Gaussian beam of X-band electromagnetic waves.
The dotted line is the trace in the plasma chamber.

 

Study: Sylvain Bolioli, Jean-Pierre Lopez, Pierre Borderies, Engineers in the Electromagnetism and Radar Department [DEMR]

Top

Last Update: November 19, 2007 - © ONERA 2009 - Terms of use