Production of negative ion plasmas using perfluoromethylcyclohexane (C$_{7}$F$_{14})$ .

Negative ion plasmas are produced by electron attachment to neutral molecules when an electronegative gas is introduced into a plasma. One of the most widely used gases is sulfur hexafluoride, SF$_{6}$ which has a relatively high electron attachment cross section for low energy ($<$0.05 eV) electrons, making it particularly attractive for use in Q machines, where T$_{e} \quad \sim $ 0.2 eV. However, in discharge plasmas having T$_{e}$ $\sim $ several eV, multiple negative ion species are also formed, including F$^{-}$, which can be corrosive to vacuum system components. As an alternative, we have investigated the use of C$_{7}$F$_{14}$ to produce negative ion plasmas, both in a Q machine and in a hot-filament, multidipole device. The maximum attachment cross-section is $\sim $ 6 times higher than that of SF$_{6}$, and occurs at a higher energy, 0.15 eV, so that the attachment efficiency should be enhanced both in the Q machine and in the discharge plasma. Details of the experimental setup and Langmuir probe characteristics obtained in the plasma with C$_{7}$F$_{14}$ will be presented.