In the Sun a proton proton collision is the first step in the production of Helium. It is also the limiting step because this collision has to happen a trillion billion times before a single particle in the next step is successful. Clearly this reactor won’t be using ordinary Hydrogen.
Typically deuterium or tritium is used in fusion experiments. Deuterium is extracted from water. Tritium is made in fission reactors by neutron activation of lithium 6.