Plasma source with electron emitter heated by RF induction coil

摘要

A plasma source comprises a thermionic emitter material (2) heated by an induction coil (7), which also provides radiofrequency energy within an electrically insulated cylindrical former (1). A cylindrical anode (10) is concentric with the emitter (2) and axially displaced therefrom, generating a potential difference between anode (10) and emitter (2). The potential difference between anode (2) and ground and axial magnetic fields causes the plasma to be extracted from the source. The emitter (2) is held at negative potential via a conductive support (5). Process gas is introduced near the emitter (2) and a secondary gas injected in the anode space. Radiofrequency excitation of the emitter generates electrons via thermionic and field effects, resulting in efficient plasma generation. Both electron generation effects contribute to a broad energy spectrum of electrons, providing effective neutralisation of the plasma. Moreover, the time varying axial magnetic field induced by the induction coil in the vicinity of the emitter (2) provides enhancement of plasma generation and confinement of the plasma to minimise erosion of the emitter (2).