Efficiency measurements of a pre-separation stage for the krypton distillation column for the XENON1T experiment

The XENON1T experiment is the next generation experiment for the direct detection of dark matter in the form of Weakly Interacting Massive Particles (WIMPS). For this purpose a dual-phase TPC, filled with xenon is used, aiming for a fiducial volume of 1 ton to increase the sensitivity to WIMP-nucleon cross section by two orders of magnitude comparing to current experiments. One dominant radioactive contamination, which one needs to reduce to reach the sensitivity, is Kr-85, which has a beta-decay with an endpoint energy of 687 keV. Therefore, the xenon has to be purified to a concentration of <0.5ppt (parts per trillion) natural krypton in xenon. For this purpose the technique of cryogenic distillation is used. In the distillation column, which is being constructed, the xenon is liquefied in a first condensing station, before it is injected to the distillation tube. This condensing station can be used as a pre-separation station, to enhance the performance of the system. In this talk the determination of the pre-separation efficiency and the impact on the design of a distillation column is presented.