Design, Construction and Assembly of Vacuum Boron Dropper Scale

As a method of plasma control, boron is inserted into magnetic fusion devices to enable real-time wall conditioning of plasma-facing components and prevent wall outgassing. We present a design to modify a boron Impurity Powder Dropper piezo feeder, such that the feeder is upgraded to include a vacuum-resistant precision weight scale to quantify the mass of boron injected into the plasma. The modification uses a method of electromagnetic force restoration applied to measure the dropper weight change and obtain the active mass and flow rate of materials within a pulse. Present material measurement techniques use light subtraction through a falling powder stream which requires calibration for a specific type of powder and is not accurate enough for quantitative measurements. This uncertainty is substantially reduced with an incremental mass measurement, eliminating the inaccuracies of light subtraction