SBIR-STTR Award

Achieving the hypervelocity potential of electromagnetic railguns is impaired by Ablation of bore materials and a lack of well validated understanding of plasma Armature performance. Development of bore materials and modeling of plasma Armatures is hampered by the lack of diagnostics which can accurately measure The in-bore environment. A key diagnostic which would be extremely useful for Both material developmentand plasma understanding is direct measurement of The very high heat flux to the bore surface. This phase i program will demonstrate A bore heat flux gage through proof-of-concept tests in an actual eml. Ouranalysis indicates that accurate bore heat flux measurements can be Accomplished by using a small slug calorimeter constructed of advanced high Temperature materials (we are considering either pyrolitic graphite or thin film Diamond coating). The gage will be place in one of thebarrel insulators to Eliminate ohmic heating issues. We will complete detailed design of the gage using A transient heat transfer computerprogram developed for the bore environment. We will fabricate a prototype gage and test in a suitable railgun, preferrably The eglin afb pug facility.

Phase I demonstrated an innovative calorimeter gage concept for directly measuring plasma armature heat transfer in electromagnetic railguns. The concept utilizes a miniature thermocouple-instrumented pyrolytic graphite cylinder. The high vaporization temperature and anisotropic properties 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. Other features minimize heat leak errors, avoid electromagnetic interference, and enable simultaneous measurement of radiation and convection heat transfer. Phase II will further develop and apply this new diagnostic to measure heat transfer to railgun insulators and rails. The gage operating range and repeatability will be demonstrated. The effort of bore size on plasma armature heat transfer, and the relative heating to the rails and insulators, will be quantified. Calorimetric heat transfer measurements will be compared with data from light emission and spectroscopic diagnostics, and with plasma armature analytical models. The railgun bore heat transfer gage technology will be transferred to other researchers to encourage application for additional measurements.