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The interferometric "Hook" method has been used to measure the copper ground-state density during the interpulse period for a 38-mm bore diameter copper vapor laser (CVL) operated in kinetically enhanced (KE) mode (Ne-HCl-H gas mixture) and in conventional mode (pure neon and Ne-H gas mixtures). It was found that the rate of regrowth of the axial copper density during the afterglow of the KE-CVL is 3-4 times faster, and the axial prepulse ground-state copper density is 2-3 times higher, than that observed for pure Ne or Ne-H buffer gases. We conclude that the primary action of the HCl H additives is to increase the interpulse plasma relaxation rate and to increase the threshold copper density beyond which thermal runaway occurs. These effects are primarily responsible for the elevated pulse rates and increased pulse energies giving improved power scaling characteristics of KE-CVL's.