A gage for measuring heat transfer to the bore of electromagnetic railguns

A calorimeter gage for directly measuring plasma armature heat transfer in electromagnetic railguns has been fabricated and tested. The concept utilizes a miniature thermocouple-instrumented pyrolytic graphite cylinder. The high vaporization temperature and anisotropic properties of the pyrolytic graphite combine to enable measurement of intense heat pulses (time integral of heat flux) beyond the capacity of any other calorimeter. Since the sensing surface does not melt or ablate, data interpretation is straightforward and gage destruction is avoided. Initial tests of the gage have been conducted in the plasma utility gun (PUG). Gage response was generally as anticipated, and heat transfer was determined at two bore locations for two PUG shots. Results from these preliminary tests indicate that heat transfer to bore insulators is less than that to the rails. Additional tests are planned including direct measurements of rail heating to confirm initial indications of the heat transfer distribution between rails and insulators