Measurement of Carbon Disulfide Anion Diffusion in a TPC

The Directional Recoil Identification From Tracks (DRIFT) detector has recently been proposed [?] to search for dark matter. This detector is unique in that it drifts negative ions, instead of electrons, in a time projection chamber (TPC). A detailed description of the operation, motivation, and other uses of a negative ion TPC (NITPC) can be found in [?]. Briefly, an electronegative component in the gas captures ionized electrons forming negative ions. These anions then drift to the anode wires where, provided the electronegative component allows it, the anions are ionized and normal electron avalanche occurs. The motivation for such an arrangement is that it allows transport of charge to the anode with the minimum possible diffusion. Using a proportional chamber, Crane showed that CS2 has the desired electronegative properties [?]. Using a single wire drift chamber of unusual design, Martoff et al. [?] measured the drift velocity and lateral diffusion of CS2 ions in two different gas mixtures. In