Taylor relaxation and λ decay of unbounded, freely expanding spheromaks
Taylor relaxation and λ decay of unbounded, freely expanding spheromaks
复制标题
无界、自由膨胀球体的泰勒弛豫和 λ 衰减
DOI：
10.1063/1.1287137
复制
发表时间：
2000
影响因子：
2.2
通讯作者：
P. Bellan
中科院分区：
文献类型：
--
作者：
J. Yee;P. Bellan
磁化的同轴电子枪被放入一个大得多的真空室中，随后使用高速摄像机和磁性探头阵列观察到等离子体的演变。摄影结果显示了四种不同的手术模式，标记为I-IV，每一种都有定性的不同动力学，参数lambdagun=µ0Igan/Phibias决定了手术模式。在区域II中产生的等离子体被鉴定为分离的球面组态。图像描绘了一个像甜甜圈一样的形状，而磁性数据表明存在一个封闭的环状磁通-表面拓扑结构。极向磁通放大表明泰勒驰豫机制在起作用。等离子体lambda=µ0Jphi/bphi的时空变化表明，球面正以类似于行星际磁云的自相似膨胀模型的方式在衰变和膨胀。在区域III中，由于过多的偏置磁通，等离子体不能从枪上分离。对环形和极向磁通以及波长分布的分析表明，在这种情况下，磁通和螺旋度仅限于火炮内部。
A magnetized coaxial gun is discharged into a much larger vacuum chamber and the subsequent evolution of the plasma is observed using high speed cameras and a magnetic probe array. Photographic results indicate four distinct regimes of operation, labeled I–IV, each possessing qualitatively different dynamics, with the parameter lambdagun = µ0Igun/Phibias determining the operative regime. Plasmas produced in Regime II are identified as detached spheromak configurations. Images depict a donut-like shape, while magnetic data demonstrate that a closed toroidal flux-surface topology is present. Poloidal flux amplification shows that Taylor relaxation mechanisms are at work. The spatial and temporal variation of plasma lambda= µ0Jphi/Bphi indicate that the spheromak is decaying and expanding in a manner analogous to a self-similar expansion model proposed for interplanetary magnetic clouds. In Regime III, the plasma is unable to detach from the gun due to excess bias flux. Analysis of toroidal and poloidal flux as well as the lambda profile shows that magnetic flux and helicity are confined within the gun for this regime.