Single beam laser induced fluorescence technique for plasma transport measurements

Abstract

A technique for measuring ion transport using laser-induced fluorescence has been developed and tested in an argon plasma. It uses only one broadband beam thus being simpler than some previous techniques because no detection beam is required. First, a 5 s laser pulse centered on 611 nm stimulates a transition from the metastable state in Ar͑II͒ 3d 2 G 9/2 to 4 p 2 F 7/2 0 . A 4p 2 F 7/2 0 to 4s 2 D 5/2 transition rapidly results with emission at 461 nm. Upon cessation of the laser pulse, the 461 nm light in the detection volume does not return to its background level immediately because the 3d 2 G 9/2 level is partially depleted. The time history of the 461 nm signal in returning to steady-state background intensity provides a means of determining ion transport because the recovery signal is due to processes including ion excitation, diffusion, convection, and thermal motion. Measurements of the ion velocity distribution yield the contributions of thermal and convective effects to ion transport. By varying the laser beam diameter and the detection volume the plasma ion spatial diffusion coefficient D, and the time, p it takes for processes other than transport to bring the 461 nm emission back to the steady-state background level are determined. For example, in one set of plasma conditions Dϭ0.58Ϯ0.16 m 2 /s and p ϭ59Ϯ7 s were found.

Three-dimensional laser-induced fluorescence measurements in a helicon plasma

“…1 LIF has been used in many types of plasma discharges, including helicon plasma sources, to measure ion flow, ion temperature, magnetic field strength, and plasma density. [2][3][4][5][6][7] Typically, these measurements are made at a single location in a plasma. Some research groups have performed planar LIF measurements in which a laser beam is spread into a sheet and used to illuminate a cross section of a plasma.…”

Two-dimensional ion velocity distribution functions in inductively coupled argon plasma

“…A collimator at the end of the fibre optic cable directed the light from the plasma through the filter and into the PMT. This system [8] has a resolution of 2 mm, but it reduces the LIF signal by a factor of 1000, and the signal-to-noise ratio is lower.…”

“…This work described here builds on the foundation of the previous work on argon plasma LIF. Edrich et al [8] have studied ion diffusion and scattering using LIF. Sadeghi et al [9] have also studied ion transport.…”

Nonlinear optical tagging diagnostic for the measurement of Fokker–Planck diffusion and electric fields

“…1 for Ar II, the velocity diffusion coefficient can be obtained with only one laser beam using nonlinear optical tagging. 3,4 The purpose of this article is to show that this nonlinear optical tagging can be extended to measure both electric field E and velocity-space diffusion coefficient D in the presence of a density perturbation associated with the propagation of an electrostatic shock.…”