Theory of evaporative cooling with energy-dependent elastic scattering cross section and application to metastable helium

A model was developed to allow simulation of evaporative cooling experiments in situations where the elastic scattering cross section depends on collision energy. The model was used to simulate the number of atoms and temperature in a rf sweep for metastable helium. The value of the scattering length was found to be very sensitive to the way the short-range and long-range potentials were connected. It was concluded that by applying the modified theory to the measurements on evaporative cooling of metastable helium, a scattering length |a| = 10(5) nm can be found