Space Plasma Physics

High power radio waves can not only form a powerful diagnostic of the space plasma environment, but can also be used in active experiments to actually change the plasma itself.  Phenomena which can be artificially-induced in the near Earth space plasma include ULF and VLF electromagnetic waves and short scale electrostatic plasma density waves and irregularities in the ionosphere and magnetosphere. These artificially generated waves and irregularities, once injected into the space plasma, can be detected by other ground-based radars and magnetometers and by satellite-born instruments in a controlled and co-ordinated manner which significantly enhances our present diagnostic capabilities.  Such experiments are performed using the EISCAT heater at Tromso, northern Norway, and SPEAR on the Svalbard archipelago.

Current experiments include

  1. Artificial irregularity generation, where small scale field aligned plasma density irregularities, with scale sizes of a few tens of metres across the geomagnetic field are generated. This provides artificial backscatter targets so that coherent backscatter radars, in general,  and the UK’s CUTLASS radars, in particular, can operate when no natural backscatter irregularities (radar aurora), on which such radars usually have to rely, are present. This greatly enhances the geophysical capabilities of the CUTLASS radars. Furthermore, it has now been established that the backscatter spectra from artificial irregularities are significantly narrower than those from natural radar aurora. As a result, artificial scatter from SPEAR irregularities will provide high resolution Doppler velocity estimates of plasma flows, particularly those associated with highly dynamical phenomena such as ULF waves.electrojet modulation experiments
  2. Artificial ULF Sounding: This involves the stimulation of ULF waves, typically in the mHz frequency band, by modulated RF heating of the electrical currents in the conduction layer (90-120 km altitude) of the polar ionosphere. This allows the structure of the magnetosphere to be sounded by means of artificially injected ULF waves, which can be diagnosed by ground based magnetometer networks as well as satellite borne instruments. It offers the exciting prospect of identifying the boundaries between open and closed field lines which determine the nature of the coupling between the ionosphere and the solar wind.
  3. Field Line Guided Wave Injection: This involves the excitation of waves in the 1-100 Hz band by modulated RF heating of ionospheric currents. These waves are guided by geomagnetic field lines and will enable field lines which thread ground and satellite locations to be identified. This will lead to improved co-ordination between ground-based and spaced-based diagnostics and in addition serves as a well defined sign post to allow the location of satellites relative to important magnetospheric boundaries.
  4. Nonlinear Interactions in the Polar Cap Plasma: High power radio wave facilities modify the ionospheric plasma in the polar cap in a controlled manner, allowing a wide variety of electromagnetic and electrostatic wave instabilities to be initiated and studied in a variety of plasma environments and magnetic field geometries.

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