A Two-Color Heterodyne Interferometry Sensor for Direct, High-Speed Electron Density Measurements in NASA EAST Facility

Planetary entry and atmospheric reentry involve very high velocities and a significant source of vehicle heating is the radiation from the high temperature, bow shock-heated plasmas formed in front of the vehicle. The radiative environment corresponding to different planetary entry conditions is simulated in the NASA Ames Electric Arc Shock Tube (EAST) facility, and there is a need for developing nonintrusive, accurate, spatially and temporally resolved diagnostic of electron number density to help improve the physics of radiative transport prediction models. nbsp; The objective of the Phase II effort is the refinement and delivery of a high-speed electron number density sensor using two-color heterodyne interferometry (TCHI) for the EAST facility. Specifically, we will build on the promising initial results from Phase I and develop a compact, robust and validated TCHI sensor integrated with EAST. Based on our initial data and additional opportunities to refine the sensor, we anticipate that electron density measurements below 1012 cm-3 with spatial resolutions of lt; 1 mm are feasible at 1 MHz rate. Further optimize and validate the TCHI system performance using surrogate plasmas. Build a more compact and robust TCHI transmitter and detector platforms, including an all-fiber detection system. Compare the free-space and fiber detection implementations of TCHI in a shock tube test. Build a laser schlieren system for accurate detection of the shock front arrival to serve as a trigger source for the TCHI sensor. Perform final integration, testing, and system performance checks at the NASA EAST facility. nbsp; The Phase II deliverables will be progress reports, a final report, two instruments ndash; a laser-schlieren system for shock front detection and the TCHI sensor, validated with measurements in the EAST facility along with their user manuals.