The proton, along with the neutron is the most common nucleon. Both species have very similar mass, however the proton has a positive charge, compared with the neutron’s zero charge.

Hydrogen, the simplest element, is made up of a nucleus containing only one proton orbited by one electron. (the other isotopes of hydrogen deuterium and tritium have in their nuclei an additional one or two neutrons respectively) In the plasma state the electrons are dissociated from the nucleus: in other words hydrogen plasma consists of protons and free electrons.