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首页> 外文学位 >Pursuing the plasma dynamo and MRI in the laboratory: Hydrodynamic studies of unmagnetized plasmas at large magnetic Reynolds number.
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Pursuing the plasma dynamo and MRI in the laboratory: Hydrodynamic studies of unmagnetized plasmas at large magnetic Reynolds number.

机译：在实验室中进行血浆动力学和MRI：在大雷诺数下未磁化血浆的流体动力学研究。

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摘要

A new method for studying flow-driven MHD instabilities in the laboratory has been developed, using a highly conductive, low viscosity, spherical plasma. The confinement, heating, and stirring of this unmagnetized plasma has been demonstrated experimentally, laying the foundations for the laboratory studies of a diverse collection of astrophysically-relevant instabilities. Specifically, plasma flows conducive to studies of the dynamo effect and the magnetorotational instability (MRI) are measured using a wide array of plasma diagnostics, and compare favorably to hydrodynamic numerical models.;The Madison plasma dynamo experiment (MPDX) uses a cylindrically symmetric spherical boundary ring cusp geometry built from strong permanent magnets to confine a large (R=1.5 m), warm (Te < 20eV), dense, unmagnetized plasma. Detailed probe measurements of plasma transport into the edge cusp have demonstrated that particle confinement follows an ambipolar diffusion model, wherein unmagnetized ions are the more mobile plasma species and total plasma transport is limited by the slow cross-field diffusion of magnetized electrons. Emissive discharge heating is shown to be an efficient method of plasma heating, but limitations caused by instabilities in the anode-plasma sheath are found to prohibit the desired access to the full dimensionless parameter space in Re and Rm.;The plasma is stirred via J x B torques using current drawn from emissive LaB6 cathodes located at the magnetized plasma edge, which also ionize and heat the plasma via sizable discharge current injection. Combination Langmuir/Mach probes measure maximum velocities of 6 km/s and 3 km/s in helium and argon plasmas, respectively, and ion viscosity is shown to be an efficient mechanism for transporting momentum from the magnetized edge into the unmagnetized core. Momentum loss to neutral charge-exchange collisions serves as the main source of drag on the bulk plasma velocity, and ionization fraction (He ∼ 0.6, Ar ∼ 0.95) is shown to be a limiting factor in momentum penetration. High Alfven Mach number flows have also been generated by drawing current across a global axial magnetic field, resulting in a velocity geometry conducive to MRI experiments. The experiment has achieved magnetic Reynolds numbers of Rm < 250 and fluid Reynolds numbers of Re < 200 (significantly higher than previous flow experiments in cusp-confined plasmas), setting the stage for future research of flow-driven MHD instabilities.
机译：已经开发出一种新的方法，该方法使用高导电性，低粘度的球形等离子体在实验室研究流动驱动的MHD不稳定性。已经通过实验证明了这种未磁化等离子体的限制，加热和搅拌，为与天体物理学相关的各种不稳定性的多种多样的实验室研究奠定了基础。具体而言，有利于研究发电机效应和磁旋转不稳定性（MRI）的血浆流量使用各种等离子体诊断仪进行测量，并与流体动力学数值模型进行比较。;麦迪逊等离子体发电机实验（MPDX）使用圆柱对称球形边界环尖齿的几何形状由坚固的永磁体构成，以限制大的（R = 1.5 m）温暖的（Te <20eV）致密的未磁化等离子体。等离子体向边缘尖部传输的详细探针测量结果表明，粒子约束遵循双极性扩散模型，其中未磁化的离子是活动性更高的等离子体种类，而总的等离子体传输受到磁化电子的缓慢交叉场扩散的限制。发射放电加热被证明是一种有效的等离子体加热方法，但是发现由阳极-等离子体鞘层的不稳定性引起的限制阻碍了对Re和Rm中整个无量纲参数空间的期望访问。使用从位于磁化等离子体边缘的发射LaB6阴极汲取的电流产生的x B转矩，该电流还会通过相当大的放电电流注入来电离并加热等离子体。 Langmuir / Mach组合探针在氦和氩等离子体中分别测得的最大速度分别为6 km / s和3 km / s，并且离子粘度被证明是将动量从磁化边缘传输到未磁化磁芯的有效机制。中性电荷交换碰撞的动量损失是整体等离子体速度的主要阻力来源，电离分数（He〜0.6，Ar〜0.95）被证明是动量穿透的限制因素。高Alfven Mach数流也已经通过在全局轴向磁场上汲取电流而产生，从而形成了有利于MRI实验的速度几何形状。该实验已经实现了Rm <250的磁雷诺数和Re <200的流体雷诺数（明显高于以前在尖端处受限制的等离子体中的流动实验），为以后的流动驱动MHD不稳定性研究奠定了基础。

著录项

  • 作者

    Weisberg, David B.;

  • 作者单位

    The University of Wisconsin - Madison.;

  • 授予单位 The University of Wisconsin - Madison.;
  • 学科 Plasma physics.;Astrophysics.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 138 p.
  • 总页数 138
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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