Mechanism study on enhancing the helicon plasma density in the target region of linear plasma device MPS-LD

To enhance the plasma density ( n e ) in the target region of the linear plasma device multiple plasma simulation linear device, the roles of helicon-wave energy transport and radial wavenumber control in H 2 helicon discharges are investigated. A fully water-cooled helicon plasma source is developed, and the H 2 helicon discharge experiments and theoretical analysis are carried out. The results show that insufficient axial propagation of helicon wave energy under the optimal discharge conditions for source region (gas flow rate fr = 300 sccm, uniform magnetic field strength B u = 200 G) is the primary factor limiting the target region n e (0.15 × 10 18 m −3 ). Optimizing the value of fr and B u ( fr = 150 sccm, B u = 150 G) can improve wave propagation and moderately enhance the target region n e (0.5 × 10 18 m −3 ). Further analysis reveals that increasing the radial wavenumber ( k ⊥ ) effectively enhances n e by promoting radial focusing of wave energy toward the region of main plasma. Based on this mechanism, a converging magnetic-field configuration is introduced to increase the target region magnetic field strength and enhance the target region k ⊥ . Under the optimal magnetic field gradient configuration, the target region n e can be further significantly increased to 1.35 × 10 18 m −3 . In addition, the n e enhancement effect in target region strongly depends on the axial transport characteristics of helicon waves, which are jointly regulated by the gas flow rate and source region magnetic field strength. This work demonstrates that optimizing axial wave energy transport and increasing the target region radial wavenumber provide an effective approach for generating high-density target region plasma in long linear helicon plasma devices.