Modification of exposure conditions downstream in the diffusion chamber has been performed in helicon antenna-excited helium plasma by adjusting the magnetic field (intensity and geometry). In the inductively coupled mode (H mode), a reduction in ion and heat fluxes is found with increasing magnetic field intensity, which is further explained by the more highly magnetized ions off-axis around the last magnetic field lines (LMFL). However, in helicon wave mode (W mode), the increase in magnetic field intensity can dramatically increase the ion and heat fluxes. Moreover, the effect of LMFL geometry on exposure conditions is investigated. In H mode with contracting LMFL, off-axis peaks of both plasma density and electron temperature profiles shift radially inwards, bringing about a beam with better radial uniformity and higher ion and heat fluxes. In W mode, although higher ion and heat fluxes can be achieved with suppressed plasma cross-field diffusion under converging LMFL, the poor radial uniformity and a small beam diameter will limit the size of samples suitable for plasma irradiation experiments.

通过调整磁场（强度和几何形状），在螺旋天线激发的氦等离子体中对扩散室下游的暴露条件进行了修改。在感应耦合模式（H模式）中，随着磁场强度的增加，离子和热通量会减少，这可以通过围绕最后一条磁场线（LMFL）轴离轴的磁化程度更高的离子进一步解释。但是，在螺旋波模式（W模式）下，磁场强度的增加会大大增加离子通量和热通量。此外，研究了LMFL几何形状对曝光条件的影响。在具有LMFL收缩的H模式下，等离子体密度和电子温度曲线的离轴峰均向内径向移动，从而使光束具有更好的径向均匀性以及更高的离子通量和热通量。