Whistler Modes in Highly Nonuniform Magnetic Fields

研究了等离子体中某些电磁波的基本性质。这些波，特别地被称为哨声模式，在空间等离子体和等离子体处理和推进中非常重要。它们还没有在等离子体中进行过研究，等离子体浸泡在高度不均匀的磁场中，磁场在一个波长或更短的范围内变化。这些波是在一个大型实验室等离子体中被激发和测量的，该等离子体具有由强永磁体和载流线圈产生的局部磁场。通过在三维空间和时间中对波磁场的三个矢量分量的详细测量，得到了波的传播、波的折射和反射、驻波和非线性效应。这些发现有望对空间等离子体中的波效应产生新的认识，并改善等离子体加工的工业等离子体源。具体来说，口哨波的传播将在磁性X型和o型零点、磁中性片和高镜像比的偶极子场附近进行研究。这种几何形状经常在空间和实验室等离子体中发现，但在磁场的空间变化与波长相当的情况下，对波的性质知之甚少。在这种情况下，可能存在不同的群速和相速，使波的传播变得复杂。实验产生了完整的数据集，为理解哨子中介的重联、闭场线上的哨子特征模、低混合频率层的哨子波反射以及月球地壳磁场附近的哨子模、小环形等离子体中的哨子、螺旋和磁控管放电中的哨子提供了有价值的见解。因此，这项研究将开辟等离子体物理学中尚未开发的领域，具有广泛的相关性。

Fundamental properties of certain electromagneticwaves in plasmas are investigated. These waves, specifically known as whistler modes, are very important in space plasmas and in plasma processing and propulsion. They have not yet been studied in plasmas immersed in highly nonuniform magnetic fields that change within one wavelength or less. The waves are excited and measured in a large laboratory plasma with local magnetic fields produced by strong permanent magnets and current-carrying coils. Wave propagation, wave refraction and reflection, standing waves and nonlinear effects are obtained from detailed measurements of three vector components of the wave magnetic field in three dimensional space and time. The findings are expected to produce a new understanding of wave effects in space plasmas and to improve industrial plasma sources for plasma processing.Specifically, whistler wave propagation will be studied near magnetic X- and O-type null points, magnetic neutral sheets and dipole fields with high mirror ratios. Such geometries are often found in space and laboratory plasmas, but there is little knowledge about the wave properties in a regime where the spatial changes of the magnetic field are comparable to the wavelength. Under those circumstances, different group and phase velocities are possible and complicate the wave propagation. The experiments produce complete data sets that provide valuable insight for the understanding of whistler-mediated reconnection, whistler eigenmodes on closed field lines, and whistler wave reflection at the lower hybrid frequency layer as well as whistler modes near lunar crustal magnetic fields, whistlers in small toroidal plasmas, and in helicon and magnetron discharges. Thus, the research will open up unexplored areas in plasma physics with broad relevance.