Plasma confinement using semi-spherical cavities for enhancement of ablative laser propulsion parameters

The influence of semi-spherical cavities of different sizes was investigated for the enhancement of propulsion parameters in conjunction with pulsed Nd:YAG laser operating at 1064 nm. The 10 mm, 11.5 mm, 15 mm, 18.5 mm and 20 mm cavities of iron were used to confine the laser-induced plasma. Aluminum (Al), Silver (Ag), and Gold (Au) samples in form of foils were used as propellants. A significant enhancement in momentum coupling coefficient (C-m) and specific impulse (I-sp) was observed when cavities were used to confine the laser-induced plasma. From the measurements obtained for various sizes of cavities, it was observed that C-m and I-sp recorded the highest values for the 10 mm cavity. Therefore, the confinement effect was most significant for the smallest cavity. In confinement geometry the value of C-m increased from 16.9 to 39.6 (dyne/W) for Al, from 13.1 to 30.6 (dyne/W) for Ag and from 12.9 to 34.5 (dyne/W) for Au target respectively, while the value of I-sp increased to nearly 40,000 s with the confined geometry, as compared with 3000 s for direct propulsion. Results demonstrated that due to uniform and balanced compression of shockwaves in all directions, semi-spherical cavities played a significant role in the enhancement of laser ablation propulsion parameters. This may introduce new avenues to tune the specific impulse and thrust in micropropulsion applications.