Neutral beam injection is a technique used in fusion research to heat and control plasma. It involves firing high-energy beams of neutral particles into the plasma, which helps to increase its temperature and stability. This process is essential for achieving the conditions necessary for nuclear fusion, where atomic nuclei combine to release energy. The neutral particles are created by stripping electrons from atoms, allowing them to penetrate the plasma without being repelled by its electric fields. This method is crucial in devices like tokamaks, which are designed to contain and sustain fusion reactions for energy production.