Mullins Carl R, Farnell Casey C, Farnell Cody C, Martinez Rafael A, Liu David, Branam Richard D, Williams John D
Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, USA.
Plasma Controls LLC, 1180 La Eda Lane, Fort Collins, Colorado 80526, USA.
Rev Sci Instrum. 2017 Jan;88(1):013507. doi: 10.1063/1.4974098.
A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current.
本文提出了一种通过远程测量磁场并求解电流密度的反问题来确定封闭漂移推进器中霍尔电流密度分布的方法。磁场是通过使用由八个隧道磁阻（TMR）传感器组成的阵列进行测量的，当置于高背景磁场中时，这些传感器具有毫高斯灵敏度。该阵列位于配备中心安装空心阴极的1.5千瓦霍尔推进器的推进器通道外侧。在传感器阵列位置，静磁场约为30 G，处于TMR传感器的线性工作范围内。此外，在此距离处的感应场约为几十毫高斯，也在TMR传感器的灵敏度范围内。由于反问题的性质，感应场测量不能通过简单的反演得到霍尔电流密度；然而，对感应场进行蒂洪诺夫正则化确实能得到电流密度分布。这些分布在等高线图中显示为时间的函数。在1.3千瓦至2.2千瓦的一系列运行条件下，测得的平均霍尔电流与平均放电电流之比在6.1至7.3之间。1.5千瓦下的时间反演解显示出24千赫的呼吸模式频率，这与放电电流的时间测量结果一致。
