Low-cost vacuum baffle based on thermoelectric cooling

J. M. CONDE GARRIDO; JOSEFINA M. SILVEYRA

Aberdeen

Simposio; 1st International Symposium on Mechanics; 2018

Many modern technological processes require clean high vacuum environments. Diffusion pumps (coupled with mechanical pumps) can achieve high vacuum pressures (3×10-8 mbar) and are relatively inexpensive and easy to maintain. Their greatest drawback is the backstreaming of oil vapors that could potentially contaminate the chamber where the process of interest is taking place.Likewise, some of these processes produce, as byproduct, contaminants that must be kept from entering into the vacuum system: the pipes and, especially, the pumps. One example is the pulsed laser deposition of thin films of alloys containing elements with high vapor pressure, such as sulfur, selenium, or tellurium. These contaminants travel down the vacuum pipes and may not only be hazardous to the operator´s health but could also degrade the properties of the oils used in the pumps.We propose a new baffle technology that overcomes the disadvantages associated with liquid nitrogen or compressor cooling systems. Our baffle is aimed at trapping both oil vapors going up the vacuum pipes (in the direction of the process chamber) and chalcogenide contaminant vapors (i.e. sulfur, selenium, or tellurium) going down the vacuum pipes (in the direction of the diffusion pump), while avoiding the undesirable partial cryopumping of water. This application does not require temperatures in the range of liquid nitrogen, but in the -50 °C to -30 °C range.We developed a virtual prototype of a low-cost baffle for vacuum systems that is cooled down with thermoelectric coolers (TECs). Compared to compressor cooling systems, TECs have useful advantages for this application: they are compact, silent, vibration-free, almost maintenance-free, inexpensive, widely commercially available, and capable of providing a precise temperature control. The baffle is partly built inside a tee vacuum fitting. A refrigerated cooper helix provides the trapping surfaces for contaminants flowing between the process chamber and the vacuum pumps. The cost of the baffle is below USD 250. The proof-of-concept model, implemented by the finite element method, showed that, when using TEC1-12706 modules, the helix can reach temperatures as low as -50 ºC. This temperature is more than enough for trapping the contaminants described above.