Measurement of ion flow velocity field associated with plasma hole using laser induced fluorescence spectroscopy

'Plasma hole' is a singular vortex spontaneously formed in an electron cyclotron resonance plasma. So far the ion flow velocity field associated with the plasma hole has been measured with a directional Langmuir probe (DLP). Here we present the first result of measuring azimuthal and radial flow velocity profiles of the plasma hole in an argon plasma using a laser induced fluorescence (LIF) Doppler spectroscopy, which demonstrates the effectiveness of LIF spectroscopy for absolute flow velocity measurement of the plasma hole. The azimuthal flow was found to be nearsonic rotation, the Mach number of which was approximately 0.65, which agreed with the previous DLP measurements. The radial flow was found to be outward and the velocity was considerably small, which is different from the previous DLP measurements of the plasma hole in a helium plasma. The possible causes of this discrepancy are discussed. (author)