Microwave excitation of a low-energy atomic hydrogen

Abstract

Performances of microwave driven compact neutral beam sources of different plasma excitation configurations have been compared in producing directed low energy atomic beams for biomolecular structural analyses. The beam sources include unique impedance matching systems in themselves for reducing the size of the source; a multi-turn spiral antenna successfully excited a hydrogen plasma in a 4 mm inner diameter Al2O3 tube by 2.45 GHz microwave power. A combination of a mirror magnetic field and electron cyclotron resonance has been found effective to realize a source operation at a low operating pressure (similar to 10(-3) Pa). This magnetic field configuration produced a hydrogen plasma with the optical emission spectrum predominated by atomic lines indicating a high degree of dissociation. The plasma excited in this type of source exhibited a mode transition like behavior which was not confirmed in other source geometries.