Experimental verification of Boltzmann equilibrium for negative ions in weakly collisional electronegative plasmas

摘要

Weakly collisional Ar-O2 electronegative plasmas are investigated in a dcmultidipole chamber. An electronegative core and an electropositive halo areobserved. The density ratio of negative ions to electrons ({\alpha}) in thenondrifting bulk is found to be 0.43. The profile of {\alpha} is found usingboth the phase velocity of ion acoustic waves and the drift velocity ofpositive ions determined by laser induced fluorescence. The experiment showsthat negative ions are in Boltzmann equilibrium with a temperature of 0.06 \pm0.02 eV. Double layers are not found separating the electronegative core andthe electropositive halo.