An electron cyclotron resonance ionization device includes a sealed vacuum chamber configured to contain a plasma, an electromagnetic wave injector to inject an electromagnetic wave into the sealed chamber, a magnetic structure for generating a magnetic field in the chamber and for generating a plasma along the magnetic field lines, the modulus of the magnetic field forming a magnetic mirror structure, with at least one electron cyclotron resonance region. The sealed chamber is a waveguide having a length that is greater than or equal to the guide wavelength corresponding to the frequency of the injected electromagnetic wave, and the plasma is ignited without prior injection of gas.