Design of a low-cost vacuum baffle

J. M. SILVEYRA; J. M. CONDE GARRIDO

Bilbao

Conferencia; X Iberian Vacuum Conference, RIVA X; 2017

In many high vacuum applications, the ongoing process generates gasses that need to be continuously evacuated. This is the case, for example, of thin films deposited by pulsed laser deposition in vacuum. During the continuous pumping, these gases -sometimes hazardous- contaminate the interior surfaces (and liquids) of the vacuum pipes and pumps. This situation imposes a frequent maintenance schedule. To minimize this, baffles are used. A baffle is simply a cold piece of surface that is placed in the way of the particles as they travel down the vacuum pipes. Particles are continuously hitting the surfaces of the pipes and being reemitted from them. However, when they hit a very cold surface, the low thermal energy they are left with is not enough to overcome the binding force and they remain ?stuck? to the surface. Traditional baffles consist on metal surfaces that block the linear path in a vacuum pipe and a coil where a liquid is circulated to keep surfaces cold. The cold liquid can be water or some refrigerated liquid (like liquid N2) that requires a compressor to keep cool. They usually cost over 1,000 US dollars and in some cases, require a supply of liquid nitrogen. In this work, we have designed and fabricated a baffle that is much cheaper and does not require liquid nitrogen or compressor since the cooling is done by means of a thermoelectric cooler (TEC, a.k.a: peltier module). On the downside, this baffle does not provide temperatures as cold as liquid nitrogen, so it is not as efficient. The baffle consists of a TEC that is placed on the atmosphere side. The heat is dissipated by a water block with water continuously circulating at ambient temperature. The cold side of the TEC is connected to a copper block with a copper rod in the middle. This rod enters the vacuum system with two o?rings pressing against the rod and the walls of a custom-made vacuum connector (made out of stainless steel). The rod is screwed into the middle of another copper rod. Along this second rod, a copper foil is soldered with the form of a helix. This design, forces the gases flowing down the vacuum pipes to circle along the helix, and thus providing a very low conductance and a very large surface of interaction kept at low temperatures.