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

Laser-induced fluorescence measurements of the transverse metastable ion velocity distribution function near a negatively biased plate in a low temperature (T_e<1 eV), low pressure (p₀<1 mTorr) dc multi-dipole argon discharge plasma have been made with a diode laser. The metastable argon ions in the 3s²3p⁴(³P)3d⁴F_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 0.3 mTorr, the transverse temperature increases along the presheath from 0.026 eV in the bulk plasma to 0.058 eV at the presheath sheath boundary