Magnetic trapping and evaporative cooling of metastable triplet helium

A cloverleaf magnetic trap is loaded from a magneto-optical trap containing 2 x 10(9) helium atoms in the metastable 2(3)S(1) state. With optical molasses and a spin polarization pulse up to 1.5 x 10(9) atoms are magnetically trapped. The vacuum limited trap lifetime is similar to12 s. Compression in 0.5 s yields a density increase to 8 x 10(9) cm(-3). With rf-forced evaporation using an exponentially shaped frequency sweep with a 5 s time constant the phase space density is increased from 1 x 10(-7) to 4 x 10(-3). The central density increases to 3 x 10(11) cm(-3), while an increase in elastic collision rate from 40 to 220 s(-1) indicates runaway evaporation.