Electron acceleration and ionization fronts induced by high frequency plasma turbulence

There are recent observations of artificial plasmas created during ionospheric modification experiments, in which intense radio waves are injected into the overhead ionosphere by ground-based transmitters. The plasma is formed just below the reflection point of the ordinary wave mode, where Langmuir and upper hybrid turbulence take place. When the plasma builds up, the radio wave is reflected at a lower altitude, and an ionization front is formed, rapidly descending to an altitude a few tens of kilometres below the initial critical layer. The ionization of the neutral gas is attributed to collisions with energetic electrons accelerated by the plasma wave turbulence. Numerical full-scale modeling of the Langmuir turbulence, electron acceleration and transport, and ionization processes are consistent with the observations. By a similarity principle, the experiment can be scaled down from the large-scale ionosphere to a metre-scale laboratory plasma, where microwaves are used instead of radio waves to induce the plasma turbulence. Such laboratory experiments under controlled conditions are now planned at Strathclyde, and may lead to new methods for electron acceleration and plasma generation in the laboratory