Study of the aerodynamic trap for containerless laser materials processing in microgravity

<jats:p>In the context of containerless laser processing of glasses in microgravity, a systematic study of the aerodynamic trap (ADT) has been done on the ground at both ambient and very high temperatures (≳2000 K). This work yielded a better understanding of the ADT and helped in improving its design. Experiments indicate that restoring force and sample stability depend upon the diffuser’s interior angle, flow rate, and ratio of sample to diffuser’s throat diameters. It was found that the trap’s potential energy curve versus position had a barrier height that increased with flow rate but decreased with increasing angle of the diffuser. Small angle diffusers show a greater spatial extent of the potential well, higher sphere-to-wall distances, and greater sample stability than larger angle diffusers. Low flow rates give quieter environments (smaller oscillations and perturbations due to the gas flow) than higher flow rates even though they are sufficient to trap the sample and 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 ≊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°–60°) operated at low flow rate (&lt;4.4 l/min with a 1 mm throat diameter). These conditions allow stable positioning for ambient as well as for high-temperature containerless materials sciences experiments on the ground and in microgravity. The sample should stay positioned and contactless even during large acceleration variations (2 g–μg) with minimum perturbation allowing its use in a KC-135 aircraft environment. Also, a spherical sample whose size varies through evaporation can be continuously trapped in a unique conical diffuser as long as its diameter is greater than that of the throat.</jats:p>