At the Karlsruhe Nuclear Research Centre (KfK) cryopumping techniques are being investigated by which the gaseous exhausts from the NET/ITER reactor can be pumped out during the burn-and dwell-times. Cryosorption and cryotrapping are techniques which are suitable for this task. It is the target of the investigations to test the techniques under NET/ITER conditions and to determine optimum design data for a proto-type. They involve measurement of the pumping speed as a function of the gas composition, gas flow and loading condition of the pump surfaces. The following parameters are subjected to variations: Ar/He ratio, specific helium volume flow rate, cryosurface temperature, process gas composition, impurities in argon trapping gas, three-stage operation and two-stage operation. This paper is a description of the experiments on argon trapping techniques started in 1990.1, 2 Eleven tests as well as the results derived from them are described. The general potential of helium cryotrapping by argon was shown, but there are several important issues which must be taken into account before a pumping concept for reactor operation will be chosen. These include backstreaming of argon in the two-stage option, the tolerance of the pump to impurities in the argon cryotrapping gas and pressure instabilities at high helium flowrates.