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Electron transport in E x B devices.

机译：E x B设备中的电子传输。

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A Hall thruster, an E x B device used for in-space propulsion, utilizes an axial electric field to electrostatically accelerate plasma propellant from the spacecraft. The axial electric field is created by positively biasing the anode so that the positively-charged ions may be accelerated (repelled) from the thruster, which produces thrust. However, plasma electrons are much smaller than ions and may be accelerated much more quickly toward the anode; if electrons were not impeded, a "short circuit" due to the electron flow would eliminate the thrust mechanism. Therefore, a magnetic field serves to "magnetize" plasma electrons internal to the thruster and confines them in gyro-orbits within the discharge channel. Without outside factors electrons would be confined indefinitely; however, electron-neutral collisions provide a mechanism to free electrons from their orbits allowing electrons to cross the magnetic field toward the anode, where this process is described by classical transport theory. To make matters worse, cross-field electron transport has been observed to be 100-1000 times that predicted by classical collisional theory, providing an efficiency loss mechanism and an obstacle for modeling and simulations in Hall thrusters.;The main difficulty in studying electron transport in Hall thrusters is the coupling that exists between the plasma and the fields, where the plasma creates and yet is influenced by the electric field. A device has been constructed at MTU's Isp Lab, the Hall Electron Mobility Gage, which was designed specifically to study electron transport in E x B devices, where the coupling between the plasma and electric field was virtually eliminated. In this device the two most cited contributors to electron transport in Hall thrusters, fluctuation-induced transport, and wall effects, were absent. Removing the dielectric walls and plasma fluctuations, while maintaining the field environment in vacuum, has allowed the study of electron dynamics in Hall thruster fields where the electrons behave as test particles in prescribed fields, greatly simplifying the environment. Therefore, it was possible to observe any effects on transport not linked to the cited mechanisms, and it was possible to observe trends of the enhanced mobility with control parameters of electric and magnetic fields and neutral density-- parameters that are not independently variable in a Hall thruster.;The result of the investigation was the observation of electron transport that was ∼ 20-100 times the classical prediction. The cross-field electron transport in the Mobility Gage was generally lower than that found in a Hall thruster so these findings do not negate the possibility of fluctuations and/or wall collisions contributing to transport in a Hall thruster. However, this research led to the observation of enhanced cross-field transport that had not been previously isolated in Hall thruster fields, which is not reliant on momentum-transfer collisions, wall collisions or fluctuations.
机译：霍尔推进器是一种用于太空推进的E x B装置，它利用轴向电场以静电方式加速航天器产生的等离子推进剂。轴向电场是通过对阳极产生正偏压而产生的，因此带正电荷的离子可以从推进器中被加速（排斥），从而产生推力。但是，等离子体电子要比离子小得多，并且可以更快地朝着阳极加速。如果电子不受阻碍，则由于电子流引起的“短路”将消除推力机制。因此，磁场用于使推进器内部的等离子电子“磁化”，并将它们限制在放电通道内的陀螺轨道中。没有外部因素，电子将被无限期地限制。但是，电子中性碰撞提供了一种将电子从其轨道中释放出来的机制，从而使电子能够越过磁场流向阳极，在此过程中，经典的输运理论对此进行了描述。更糟糕的是，观察到的跨场电子传输是经典碰撞理论所预测的100-1000倍，这为霍尔推力器的效率损失机制和建模与仿真提供了障碍。在霍尔推进器中，等离子体与磁场之间存在耦合，等离子体在其中产生并受到电场的影响。在MTU的Isp实验室建造了一种器件，即霍尔电子迁移率仪，该器件专门设计用于研究E x B器件中的电子传输，实际上消除了等离子体和电场之间的耦合。在该装置中，缺少霍尔推力器中电子传输，波动引起的传输和壁效应的两个最常提及的贡献者。去除电介质壁和等离子体波动，同时保持真空中的场环境，可以研究霍尔推进器场中的电子动力学，其中电子在规定的场中充当测试粒子，从而大大简化了环境。因此，有可能观察到对运输的任何影响，这些影响都与所引用的机制无关，并且有可能观察到迁移率随电场和磁场控制参数以及中性密度而变化的趋势。霍尔推力器；研究的结果是观察到的电子传输是经典预测值的20-100倍。流动计中的跨场电子传输通常低于霍尔推力器中的电子，因此这些发现不会抵消波动和/或壁碰撞对霍尔推力器中的传输造成影响的可能性。但是，这项研究导致观察到增强的跨场传输，这在霍尔推力器场中以前是无法被隔离的，它不依赖于动量传递碰撞，壁碰撞或波动。

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