The alpha process (or alpha ladder) is a sequence of nucleosynthesis steps, by which elements are synthesized in extreme heat (e.g., inside stars). Each step is a the combination of an alpha particle (basically, a helium nucleus) with another nucleus (e.g., of carbon or oxygen, etc.) during a collision between them. A nucleus undergoing this repeatedly transforms into heavier elements that have even atomic numbers, from carbon up to iron and beyond. This sequence of elements is thought of as the nucleus climbing a ladder. These even-numbered elements are the most abundant metals. At some steps, the nucleus may be unstable and beta decay may occur before another alpha particle is consumed. The beta decay lowers its atomic number by one, a way in which odd-numbered elements are formed.
The process has a high temperature/density requirement, only met in some early stars, essentially what is termed silicon burning, which is the alpha process starting with silicon. The alpha process also occurs in supernovae.