An ion implantation machine includes an enclosure that is connected to a pump device, a negatively polarized substrate-carrier that is arranged inside the enclosure, and a plasma feed device in the form of a generally cylindrical body extending between an initial section and a terminal section, the device having a main chamber provided with an ionization cell, the main chamber being provided with a gas delivery orifice, and the final section of the main chamber being provided with a head-loss component for creating a pressure drop relative to the body. Furthermore, the plasma feed device also includes an auxiliary chamber arranged beyond the final section, the auxiliary chamber opening out into the enclosure at the terminal section.