Laser-induced photodetachment in high-density low-pressure SF6 magnetoplasmas

Using laser-induced phetodetachment (LIPD), we investigate in some detail h ow different discharge parameters affect the negative ion fraction in high- density low-pressure SF6 magnetoplasmas sustained by the propagation of ele ctromagnetic surface waves. A plane electrostatic probe is used for collect ion of the photodetached electrons. Careful testing of the LIPD technique i tself is carried out prior to systematic measurements and adequate laser fl uence conditions are determined. Negative ions are found to outnumber elect rons several times, even at mTorr and submTon pressures, indicating the imp ortant electronegative character of the discharge. The dependence of the ne gative ion fraction on gas pressure, argon admixture, microwave power, and axial and radial position in the reactor is interpreted on the basis of dif ferent negative ion formation and loss mechanisms. The negative ion fractio n is found to be maximum in conditions and regions of minimal electron temp erature and positive ion density. (C) 2000 American Vacuum Society. [S0734- 2101(00)00305-5].