Conceptual Layout of Vertical Linear Sensor Arrays
Although the reactor is equipped with high-resolution spiral sensor arrays at the top and bottom, pinpointing the exact location of a bubble near the center can still be challenging. This difficulty arises from increased triangulation uncertainty due to small-angle approximation errors as the bubble moves farther from the sensor elements.
Vertical Linear Sensor Arrays (VLSAs) primarily determine the z-component of the bubble’s location, while the x and y components are resolved by the spiral sensors. Higher-resolution sensing is achieved by selectively turning individual fibers in a bundle on or off. The VLSAs serve a dual purpose—their secondary function is to supply the laser pump flux used to ignite the fuel.
Figure 10 shows a bubble beginning to pass between sensor elements F5 and F7, blocking the light that normally passes between them. This occultation will be detected when this pair is scanned during the next sensor sweep.
The arrows in Figure 10 illustrate the flow of fluid driven by natural convection currents, which occur when hot FLiBe encounters the cooler metal of the spherical wall.
Figure 9 shows where the F-cross section of Figure 10 is taken from (dotted box), and how multiple VLSAs can be arranged. Each VLSA has a narrow field of view from a specific angle. These views overlap in the central region so that, even if a fuel bubble isn’t centered in a vertically rising FLiBe column, it’s still likely to be detected by at least one array. Multiple arrays not only improve spatial resolution but also increase the maximum rate of laser pumping.