(a) Three-level LIF scheme and (b) hyperfine structure of 605.278 nm line of the odd isotopes due to nuclear spin splitting.
Argon ion parallel velocity distribution functions in (a) HELIX at and (b) HELIX at . The thick black lines are LIF signals; the thin lines are Gaussian fits assuming a single and a dual ion population line; and at the top is the iodine reference spectrum. The ivdf evolves from unimodal at into bimodal at .
(a) Individual ion sound speeds (circles for and triangles for ) and the system sound speed (open squares) as function of xenon fraction in HELIX at . (b) Parallel ion flow speeds in HELIX at vs xenon fraction (same symbol assignment).
At in HELIX, the LIF amplitude (a) and parallel flow speed (b) as function of small changes in the xenon fraction. Filled and open symbols denote the fast and slow ion group, respectively. (b) The (solid line) and system (dotted line) sound speeds calculated based on measurements at .
(a) LIF amplitude and (b) parallel flow speed as function of xenon fraction at in LEIA. Filled and open symbols denote the fast and slow ion groups, respectively. (b) The (solid line) and system (dotted line) sound speeds calculated based on measurements at .
(a) Normalized LIF amplitude and (b) parallel flow speed at (open symbols) and (filled symbols) in HELIX vs argon fraction, respectively. Also shown in (b) are the (solid line) and system (dotted line) sound speeds based on local measurements.
(a) Normalized LIF signal amplitude and (b) parallel flow speed vs input rf power in HELIX at (open symbols) and (filled symbols). (b) Bohm speed at . Operating conditions: , , , and .
Effect of increasing helium fraction on the parallel ivdf in HELIX. Measurements were obtained at .
(a) Dependence of the metastable population obtained from integration of the ivdfs and normalized to the pure Ar case (filled squares) and ratio of slow/fast LIF signals (light filled squares) vs helium fraction. (b) Parallel velocity of the fast (filled circles) and slow (open circles) populations; the (solid line) and system Bohm (dotted line) speeds, respectively; the dashed line intersecting the full circles is the theoretical dependence . (c) Bimodal ivdf with fast and slow populations for 0% He. (d) for a 30% He fraction the ivdf exhibits a long tail characteristic of charge-exchange collisions. Measurements obtained at in HELIX.
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