Plasma laser induced fluorescence (LIF)

What LIF does: LIF directly measures the ion velocity distribution function f(x,v,t).

How LIF works: A tunable dye laser pumps a bound electron from quantum level E1 to a higher level E2. The excited electron then spontaneously decays to a lower level E3, emitting a photon. By using a very narrow band dye laser, the line width of the exciting laser line is substantially narrower than the thermal Doppler width of the plasma ions so that scanning the dye laser wavelength map out the ion velocity distribution f(x,v,t).

Encore tokamak used for plasma LIF studies
What we have learned: Our LIF investigations show that ion temperature increases nearly two orders of magnitude faster than predicted by classical mechanisms. This rapid heating is caused by a naturally occuring drift wave in Encore. Although the drift wave is coherent, above a critical amplitude it causes the ions to develop stochastic trajectories. The stochasticity is surprising because it occurs for frequencies below the ion cyclotron frequency. Analytic and computer models support this interpretation.


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