Fusion plasmas are typically generated from ionization of a neutral gas. In most cases, an isotope of hydrogen — called deuterium — is used as the plasma fuel. These plasmas are therefore primarily made up of deuterium ions (plus electrons), and it is necessary to diagnose the behavior of these ions if the relevant plasma physics is to be understood. However, in any fusion device, other types of ions ("impurities") are also present. These exist naturally due to the inability to achieve a perfect vacuum in a fusion reactor before fueling. Thus, materials such as water vapor, nitrogen, and carbon will be found in small amounts in typical plasma discharges. Impurities may also be generated during plasma discharges due to plasma-wall interactions. These interactions primarily cause material from the wall to be ejected into the plasma through sputtering. In the Madison Symmetric Torus (MST), properties of the impurity ions (e.g. carbon, oxygen, etc.) are closely linked to properties of the deuterium ions as a result of strong interaction between the ion species. Thus, impurity ion measurements can, in principle, provide direct information about the deuterium ions. Measurements of the impurity ion temperature ("T"i) and flow velocity ("v"i) are obtained on MST using Charge Exchange Recombination Spectroscopy, or CHERS.