Experimental studies of transverse metastable ion velocity distribution functions in the presheath of a weakly collisional argon plasma

Laser-induced fluorescence (LIF) measurements made with a diode laser have measured the transverse metastable ion velocity distribution function profile near a negatively biased plate in a low temperature $(T_e < 1 eV)$, low pressure $(p_0 < 1 mTorr)$ dc multidipole argon discharge plasma. The metastable argon ions in the $3s^23p^4(3P)3d\:^4F_{7/2}$ state are found to be characterized by a Maxwellian temperature transverse to the direction normal to the plate. For a neutral pressure of 0.3mTorr, the transverse temperature increases along the presheath from 0.026 eV in the bulk plasma to 0.058 eV at the presheath sheath boundary. This result is compared with PIC code simulations\footnote{A. Meige, {\em et al.}, Phys. Plasmas, 14, 032104 (2007)} and experimental results\footnote{N. Claire, {\em et al.}, Phys. Plasmas, 13, 062103 (2006)} found in the literature.