Liquid Metal Mass Flow Measurement by an Inductive Proximity Detector for Use in Conjunction with a JxB Pump
A J×B feed system incorporating a variable magnetic field strength and translating inductive proximity detector has been designed to deliver and measure liquid metal mass flow rates in the range of 0 - 100 mg/s. Electric thruster research using metallic propellants under laboratory conditions requires sensitive control of low propellant mass flow rates. Previous mechanical and J ×B systems have struggled to control and accurately measure flow rates less than 100 mg/s. Existing theory describing the behavior of J×B feed systems was applied to optimize the physical dimensions and magnetic field strength of a prototype J ×B pump for low mass flow rate operation with liquid lithium. To meet the challenge of measuring the mass flow rate, an inductive proximity detector was incorporated to track the change in the propellant column height in the feed system reservoir to calculate the mass flow rate. Successful operation using liquid lithium was demonstrated for mass flow rates of 0.21-0.46 mg/s with a maximum error of ±0.13 mg/s.