Large numbers of cold metastable helium atoms in a magneto-optical trap

We report loading of 1.5×10⁹ metastable triplet helium atoms in a large magneto-optical trap, using far-red-detuned laser beams. We fully characterized this trap by measuring trap losses and absorption of a probe beam. From the highly nonexponential trap decay we derive Penning ionization loss rate coefficients for two detunings: 5.3(9)×10^-9cm³/s at -35MHz and 3.7(6)×10^-9cm³/s at -44MHz. Also, we find that the loss rate is maximum at -5MHz detuning, where the rate is 1.3(3)×10^-8cm³/s, much larger than recent theoretical and experimental values. In the absence of light the S-S ionization rate constant is measured to be 1.3(2)×10^-10cm³/s.