Thermal Imaging Helps Develop Plasma Rocket

About a month ago I wrote a post about Thermal Imaging and mentioned its growing use in areas like research.  A good example of IR imaging in a research field is its use in studying the heat transfer characteristics of the Plasma Rocket invented by Dr. Franklin Chang Diaz (VASIMR). I just finished reading this article from the International Journal of Heat and Mass Transfer that explains how data from an infrared camera is used in a numerical model to understand the heat transfer from the plasma to the quartz tube that encloses the plasma near the helicon antenna.

The plasma is contained inside a previously vacuumed quartz tube using magnetic fields. However, heat transfer from the plasma to the quartz occurs through thermal radiation.

In an attempt to quantify the radiation heat transfer rate, the outside temperature of the quartz tube is monitored with an IR camera over time. This information is used to model a 3-dimensional transient heat conduction problem of the quartz tube. Because the inside boundary condition (radiation heat transfer rate) is not known, an inverse heat transfer problem solution technique was required. The outside surface of the quartz tube was modeled as insulated. The IR data was used as known surface temperatures to compare and converge a numerical solution.

In this study the helicon antenna radio wave power was varied from 5.8 kW to 16.2 kW. Results indicate that the radiation heat transfer rate, for these power levels varied from 34.4 percent to 46.1 percent of the applied radio wave power. On average, radiation heat transfer rate from the plasma to the quartz tube was 40 percent of the applied radio wave power of the antenna. These results indicate that on average, 60 percent of the antenna power is being used produce the plasma while 40 percent is wasted in the form of heat. Knowing this information is critical when designing proper cooling methods for the rocket to prevent thermal failure.

Note: All pictures and data taken from:

Mulcahy, J., M., Browne, D., J., Stanton, K., T., Chang, F., R., Cassady, L., D., Berisford, D., F., Bengtson, R., D., 2009, “Heat flux estimation of a plasma rocket helicon source by solution of the inverse heat conduction problem”, International Journal of Heat and Mass Transfer, 52, pp. 2343-2357