STUDY OF THE AERODYNAMIC TRAP FOR CONTAINERLESS LASER MATERIALS PROCESSING IN MICROGRAVITY

In the context of containerless laser processing of glasses in microgr avity, a systematic study of the aerodynamic,trap (ADT) has been done on the ground at both ambient and very high temperatures (>2000 K). Th is work yielded a better understanding of the ADT and helped in improv ing its design. Experiments indicate that restoring force and sample s tability depend upon the diffuser's interior angle, pow rate, and rati o of sample to diffuser's throat diameters. It was found that the trap 's potential energy curve versus position had a barrier height that in creased with flow rate but decreased with increasing angle of the diff user. Small angle diffusers show a greater spatial extent of the poten tial well, higher sphere-to-wall distances, and greater sample stabili ty than larger angle diffusers. Low flow rates give quieter environmen ts (smaller oscillations and perturbations due to the gas flow) than h igher flow rates even though they are sufficient to trap the sample an d damp external perturbations. Heat loss by forced air cooling is thus reduced, enabling the processing of larger samples for a given laser power. The research suggests that for dielectric samples of approximat e to 3 mm diameter, at ambient, as well as at high temperature, where stability is a necessity, the ADT should be a small angle diffuser (30 degrees-60 degrees) operated at low flow rate (<4.4 1/min with a 1 mm throat diameter). These conditions allow stable positioning for ambie nt as well as for high-temperature containerless materials sciences ex periments on the ground and in microgravity. The sample should stay po sitioned and contactless even during large acceleration variations (2 g-mu g) with minimum perturbation allowing its use in a KC-135 aircraf t environment. Also, a spherical sample whose size varies through evap oration can be continuously trapped in a unique conical diffuser as lo ng as its diameter is greater than that of the throat. (C) 1996 Americ an Institute of Physics.