Plasma tubes becoming collimated as a result of magnetohydrodynamic pumping
Plasma tubes becoming collimated as a result of magnetohydrodynamic pumping
复制标题
等离子管由于磁流体动力泵而变得准直
DOI：
10.1063/1.3437075
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
P. Bellan
中科院分区：
文献类型：
--
作者：
G. Yun;P. Bellan
准直磁化等离子体结构通常在星系、恒星和实验室尺度上被观察到。加州理工学院的等离子体枪通过施加类似于这些等离子体的边界条件，产生了与天体物理喷流和太阳日冕环惊人相似的磁驱动等离子体射流。本文提出了对枪产生的等离子体射流的实验观察，支持先前提出的磁流体动力学（MHD）泵送模型[P. M. Bellan, Phys]。等离子体，1999(2003)]作为一种普遍准直机制。对于任何具有有限轴向电流的初始张开磁化等离子体管，该模型预测：(1)等离子体粒子从收缩区磁泵入凸起区；(2)如果在凸起区流动变慢导致质量积累，从而集中在质量流中冻结的方向磁通量（即增加夹紧力），则管准直。对枪射等离子体的时间和空间分辨光谱测量证实了导致准直状态的过程的高动态性质，即：(i) Alfvenic时间尺度下的超热Alfvenic流（30-50 km/s）， （ii）从~ 10^（17）到~ 10^(22)m^（−3）的大密度放大（5-10 μs），以及（iii）根据高速相机成像，流锋（管准直发生的地方）的流动减慢和质量积累。这些观测结果与MHD抽运模型的预测一致，并为实验室、太阳和天体物理等离子体结构的形成机制提供了有价值的见解。
Collimated magnetized plasma structures are commonly observed on galactic, stellar, and laboratory scales. The Caltech plasma gun produces magnetically driven plasma jets bearing a striking resemblance to astrophysical jets and solar coronal loops by imposing boundary conditions analogous to those plasmas. This paper presents experimental observations of gun-produced plasma jets that support a previously proposed magnetohydrodynamic (MHD) pumping model [ P. M. Bellan, Phys. Plasmas 10, 1999 (2003) ] as a universal collimation mechanism. For any initially flared, magnetized plasma tube with a finite axial current, the model predicts (i) magnetic pumping of plasma particles from a constricted region into a bulged region and (ii) tube collimation if the flow slows down at the bulged region leading to accumulation of mass and thus concentrating the azimuthal magnetic flux frozen in the mass flow (i.e., increasing the pinch force). Time- and space-resolved spectroscopic measurements of gun-produced plasmas have confirmed the highly dynamic nature of the process leading to a collimated state, namely, (i) suprathermal Alfvenic flow (30–50 km/s), (ii) large density amplification from ~ 10^(17) to ~ 10^(22) m^(−3) in an Alfvenic time scale (5–10 μs), and (iii) flow slowing down and mass accumulation at the flow front, the place where the tube collimation occurs according to high-speed camera imaging. These observations are consistent with the predictions of the MHD pumping model, and offer valuable insight into the formation mechanism of laboratory, solar, and astrophysical plasma structures.