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The Cryogenic Pumping Section

Freezing out the remaining Tritium
Principle of cryo-sorption of Tritum on Argon frost.
Schematics of Cryogenic Pumping Section. The sections below 4 K are used for cryo-sorption of Tritum on Ar-frost surfaces.

In this section all remaining traces of Tritium will be trapped by cryo-sorption onto the special prepared cold surfaces of the beam tube. For this, the gold plated beam tube will be covered at 6 Kelvin with Argon frost, which has been demonstrated to be an effcient coating for cryo-sorption of Tritium [1]. As in the case of the DPS, the beamline has a schicane to block the line of sight for the diffusing Tritium gas and  to increase the probability that Tritium molecules hit the wall. The electrons are guided up to 5.6 Tesla unaffected by the cryotrap by magnetic fields towards the spectrometer. After approximately 60 days of operation the surface is saturated with Tritium and the system is warmed up to 100 K releasing the trapped Tritium. In  parallel the released Tritium is removed by turbomolecular pumping with a cold valve being closed towards the spectrometers.

So at the end of the CPS, all tritium has been taken out of the beam, suppressing the partial pressure of tritium by 12 orders of magnitude compared to the inlet in the middle of he WGTS. On the other hand, the electron flow has been unaffected and has been guided adiabatically towards the spectromter. Now it is the task of the spectrometers to analyze as precisely as possible the kinetic enery of the beta electrons.

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