Plasmas created by the microwave torch Torche a Injection Axiale (TIA)
, which are around 2 mm in diameter and 15 mm long, are investigated.
In these plasmas large gradients are present so that the edge is suppo
sed to play an important role. Using global Thomson scattering measure
ments, in which global refers to the fact that the size of the laser b
eam is approximately equal to the diameter of the plasma, the electron
densities and temperatures were determined. However, these results le
ad to discrepancies in the particle balance: the production of free el
ectrons is much larger than the classical losses due to recombination,
convection and diffusion. Radially resolved Thomson scattering measur
ements show the plasma has a hollow structure. Although this enhances
the losses due to diffusion, still a large discrepancy remains between
production and destruction of free electrons in the argon plasmas. Pr
obably some molecular processes are significant as well. A good candid
ate is the charge transfer between argon ions and nitrogen molecules,
since mixing with the surrounding air has a large impact on the plasma
.