Charge-exchange spectroscopy (abbreviated CES or CXS) is a technique commonly used in plasma diagnostics to analyze high-temperature controlled fusion plasmas. In fusion plasmas, the light elements tend to become fully ionized during operation, which makes it challenging to diagnose their properties using conventional optical diagnostics. To address this, a method was developed in the 1970s which involves the injection of a beam of neutral atoms, such as hydrogen or deuterium, into the plasma. This process results in the ionization of hydrogenic atoms the excitation of ions through charge exchange, as represented by the reaction: