Radial Density Profiles of Fluorine Negative Ions and Electrons around a Magnetized String Plasma in CF4Gas

Radial density profiles of electrons and fluorine negative ions around a string-type CF4 plasma across a magnetic field are measured using a wire-type Langmuir probe. Modified Bohm theory is applied to evaluate negative-ion density, and it is confirmed that negative ions are well confined between two end plates. Parameter dependences of the density profiles are also measured. Simple density models for electrons and negative ions are proposed, and their radial density profiles are obtained by solving the equations of continuity. The experimental and theoretical results are in good agreement for electrons, whereas there are some discrepancies for negative ions. An unexpected small recombination rate coefficient of negative ions and radial electric field might be the reason for this discrepancy.