Analysis technique for ejecta cloud temperature using atomic spectrum

• Time-integrated UV spectra of ejecta cloud are measured.
• Excitation temperatures of ejecta cloud are measured by Boltzmann diagram method.
• Both effects of temperature distribution and self-absorption on results are discussed.
• Uneven temperature distribution is slight contribute to fitting procedure.

Eight hypervelocity impact tests of aluminum projectiles impacting aluminum plates were conducted using two-stage light gas gun. The diameters of projectile ranged from 2.0 mm to 5.0 mm, the impact velocities varied from 3.0 km/s to 6.0 km/s, and all tests were normal impacts. The time-integrated UV spectra of ejecta cloud were measured by use of a commercially spectrograph and an intensified charge-coupled device camera. Six aluminum peaks and two concomitant peaks were identified in the emission spectrum. Then the effects of the concomitant peaks were analyzed and decoupled. On the basis of spectral data, the ejecta cloud temperatures were analyzed using the Boltzmann diagram method. The effects of the uneven temperature distribution of ejecta cloud and radiation self-absorption on the measured results were discussed. It is found that self-absorption within the ejecta cloud is the predominant reason for the data points lying far from the fitting-line and should therefore be considered. Conversely, the uneven temperature distribution of the ejecta cloud is not found to significantly contribute to the fitting procedure. The temperature measured by Boltzmann diagram method is the excitation temperature. Moreover, it is found that the measurement result is the “average” temperature over both time and space, and the result tends to be shifted to the highest temperature of the ejecta cloud.