The experimental investigation and development of novel thermal barrier material passes by a characterization and measurement of plasma jet properties under various conditions of enthalpy and velocity. The experimental measurements of plasma jet parameters such as: the specific enthalpy, plasma temperature, velocity, and heat flux have been achieved using intrusive measurement techniques. This method of plasma characteristics is based on the suitable design of mechanical probes able to sustain high thermal energy and forces and are represented in the fig. 5. The fact that the samples manipulator is mounted with 4 cooled arms, on which different probes are installed, allow to have simultaneous measurement of physical parameters of the plasma jet, described above, during the same test. The 3 axis rotary arms can achieve measurement close to nozzle exit plan and few centimetres downstream of the plasma jet (Fig. 3). The stationary heat flux probes have been used to measure heat flux at 350 kW of the ICPT system. The stationary probe is water cooled and mounted with a heat transducer which is cooled separately and called Gardon gage and described well in the literature [2]. The non-intrusive diagnostic plasma techniques have been conducted via different windows disposed on the vacuum chamber. Those techniques are used for front material surface temperature measurement, performed using an optical measurement instrument such as IR camera and Pyrometer. A very thin thermocouple of 0.02’’ in diameter is inserted inside the material. Thus, the results obtained with fast response thermocouple are reported with the surface temperature measurements of the material using optical techniques. [5] The main objective from those techniques is to study the ablative materials at high heat flux levels and provide a database on precise information about the materials to be characterized and developed for thermal barrier protection used for re-entry of space shuttle. Both IR camera and pyrometer used on this experimental measurement of surface temperature behavior are operating in the close spectral range near infrared to avoid measuring the light coming from the plasma. The IR camera is operating in spectral range of 0.9 to 1.7 μm. It is provided with 2 calibrated intensity filter allowing measurement from 500-1200°C and from 1200-3000°C respectively. The pyrometer used is operating bi-chromatic which measures the intensity of infrared radiation at two different wavelengths (ʎ1 = 950 nm and ʎ2 = 1050nm) at the same time. The ratio of these two intensities is proportional to the temperature. Thus, a two-color pyrometer measurement is not influenced by emissivity changes or obstructions within the sight path such as dust or water vapor. It has been demonstrated that using some experimental set-up and rules before starting plasma, the data collected under high enthalpy and velocity flow, can be used, with confident, to characterize and qualify the material to be used as a thermal barrier material on aerospace shuttle vehicles.
