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The Differential Pumping Section

Pumping with Turbomolecular pumps
DPS2F_CAD.jpg
CAD model of DPS
DPS_photo.jpg
Photo of Differential Pumping Section
FTICR_Foto.jpg
Photo of FTICR , 310 mm in length and 83 mm in diameter.

The DPS2F is a pumping section consisting of five 1 m long beam tubes within a superconducting solenoid. To block the line of sight towards the spectrometer for the diffusing, neutral tritium molecules two sections are tilted by 20 degree. Between each section there is a turbomolecular pump with a nominal pumping speed larger than 2000 l/s.

 Schematics of DPS

In a series of dedicated test measurements it was possible to show, that the reduction factor of the DPS amounts to 2.5x104 [1]. Besides the tritium flow reduction the beam pipe of the DPS hosts instrumentation to analyze and reduce  the ion flow. Ions, mostly produced by  the decay of tritium into positive charged Helium, follow as charged particles or in form of positive charged molecules the magnetic fields and are blind against the pumping measures. But again, also the charged tritium is not allowed to enter the spectrometers, in order to keep background levels for the neutrino mass search sufficiently low. One trick is to bias the WGTS source and DPS by a little but known negative voltage. This prevents the positive charged ions or molecules to leave the source and DPS section. However, one has to get rid of the positive ions, as otherwise by time the source and DPS would charge significantly electrically up. To actively remove positive ions the DPS hosts with dipole electrodes and Fourier transformation Ion Cyclotron Resonators two kind of instrumentation to analyze the ion species (FTICR) and sweep them out of the beam tube (FTICR&dipoles).

Proceed to Cryogenic Pumping Section ...

 

Further external links

External link to group working on FTICR