Background
The buffer-gas loading technique uses cold helium gas to cool paramagnetic atoms and molecules to temperatures low enough such that they are trapped by magnetic fields. The process occurs in a cryogenic environment of ~500 mK and employs magnetic fields of a few Tesla. Once trapped, the helium buffer gas is removed leaving a thermally isolated sample which can be further cooled by evaporation. This technique has successfully trapped up to 10 ^13 europium, chromium, and molybdenum atoms. In past work, the helium buffer gas was removed by cooling the walls of the trapping chamber to a temperature (below 150 mK) where the vapor pressure of helium is negligible. The large magnetic moments of these atoms (6 or 7 Bohr magneton) ensured that the atoms remained trapped during the several seconds in which the walls were cooled and the helium buffer gas was removed.

General Description
In this experiment, we extend the buffer-gas loading method to atoms with smaller magnetic moments. This allows us to combine the advantages of the buffer-gas technique (large number of trapped atoms and applicability to a variety of atomic species) with the excellent collisional properties of metastable He, for example. By evaporatively cooling He* from the loading temperature (~500 mK) to quantum degeneracy, we hope to produce quantum degenerate gases of ten billion atoms or more (~1000 times larger than presently achievable with laser-cooled atoms). Condensates of He* of this size would provide an exceptionally bright source with high detection efficiency for use in atom lasers and interferometers. In addition, because buffer-gas loading can simultaneously load multiple species, a trap sample of this size could act as a refrigerant to sympathetically cool atoms and molecules whose intra-species collisional properties would otherwise prevent them from being cooled to quantum degeneracy.

Large aperature, fast acting, cryogenic valve (LFV)
In a radical departure from our previous methods, the helium buffer gas is pumped from the trapping chamber through a large aperture, rapidly actuating valve to a region filled with charcoal sorb. The valve is actuated by a room-temperature pneumatic cylinder and drives a Teflon seal against an alumina gasket. With this valve, the hold time for buffer gas inside our cell is greater than 1000 s, and the gas can be pumped away in ~50 ms. Therefore the time to remove the buffer gas is now much shorter than the lifetime of the trap sample. This enables the trapping and thermal isolation of low magnetic moment atoms and molecules.

Cryogenic apparatus
The LFV enables us to use a simple He3 refrigerator, greatly simplifying the experimental design. In addition to the LFV and He3 fridge, the experimental apparatus incorporates a specialized miniature cryogenic gas-handling system and 4.1 Tesla deep superconducing magnetic trap. The magnetic trap used in this experiment is the deepest ever made to our knowledge.

Sitting inside the bore of the superconducting magnet is a double-walled plastic cell made of G10. Atoms and molecules can be produced inside the cell via an ablation or rf-discharge. The cell and the helium buffer gas inside it is cooled to 400 mK by the He3 fridge via a superfluid helium thermal link. This electrically insulating cell allows the magnetic trapping fields to be changed rapidly without inducing undesirable eddy currents.