布拉德圆盘发电机的实现
Realization of Bullard's disc dynamo
摘要：
我们报告的实验结果，从三个成功运行的布拉德型单极圆盘发电机。该装置由半径为30 cm且厚度为3 cm的铜盘组成，该铜盘同轴地放置在相同尺寸的平坦的多臂螺旋线圈下方，并且通过滑动液体金属接触件在中心处和沿着圆周电连接到该线圈。磁场使用固定在线圈顶面上的霍尔探头测量。我们还测量了线圈两端的径向电压降。当盘旋转速率达到$Ω\approx 7$ Hz时，磁场急剧增加，在线圈的中心部分接近$B_{0}\approx 40$ mT。这个磁场比背景磁场强两个数量级以上。在前两次运行中，在发电机状态下制动盘的电磁转矩超过驱动盘的电动机的击穿转矩。结果，发动机熄火，发电机中断。当驱动频率设置得更高且增加得更快时，在第三次运行中没有发生失速。我们还提出了一个扩展的圆盘发电机模型，定性地再现了实验结果。
英文摘要：
We report experimental results from three successful runs of a Bullard-type homopolar disc dynamo. The set-up consisted of a copper disc with a radius of 30 cm and thickness of 3 cm which was placed co-axially beneath a flat, multi-arm spiral coil of the same size and connected to it electrically at the centre and along the circumference by sliding liquid-metal contacts. The magnetic field was measured using Hall probes which were fixed on the top face of the coil. We measured also the radial voltage drop across the coil. When the disc rotation rate reached $Ω\approx 7$ Hz, the magnetic field increased steeply approaching $B_{0}\approx 40$ mT in the central part of the coil. This field was more than two orders of magnitude stronger than the background magnetic field. In the first two runs, the electromagnetic torque braking the disc in the dynamo regime exceeded the breakdown torque of the electric motor driving the disc. As a result, the motor stalled and the dynamo was interrupted. Stalling did not occur in the third run when the driving frequency was set higher and increased faster. We also propose an extended disc dynamo model which qualitatively reproduces the experimental results.
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