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Creators/Authors contains: "Zepp, M"

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  1. ; ; (, Physics of Plasmas)
    A direct measurement of the particle balance and derivation of the underlying particle source rate distribution in a helicon plasma developed for wakefield particle accelerators is presented. Parallel and radial ion fluxes are measured using laser induced fluorescence on single ionized argon. We find that the radial contribution to the source rate is an order of magnitude larger than the axial contribution. We also find that the axial source rate profile closely matches the radial density gradient axial profile, thus indicating the importance of the radial density profile for the particle balance. Notably, the peak ion source rate is located off-axis, about halfway between the axis and the vacuum wall on both sides of the axial center. 
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  2. ; ; (, Physics of Plasmas)
    Whistlers are magnetized plasma waves in planetary magnetospheres. Bounded whistlers, known as helicons, can create high-density laboratory plasmas. We demonstrate reversal of the plasma discharge direction by changing either antenna helicity or magnetic field direction. Simulations reproduce these findings only in the presence of a radial density gradient. Inclusion of such a gradient in the wave equation gives rise to azimuthal shear currents, which for the first time consistently explains the preference of right- over left-handed whistlers and the discharge directionality in helicon plasmas. 
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