Measurement of the gas-flow reduction factor of the KATRIN DPS2-F differential pumping section

TL;DR

This study measures and simulates the gas-flow reduction factor of the KATRIN DPS2-F section, confirming the effectiveness of the design and identifying factors affecting its performance.

Contribution

It provides the first detailed measurement and simulation of the reduction factor for the KATRIN DPS2-F, including for tritium, with insights into design modifications.

Findings

Measured reduction factor for gases with mass 4 is 1.8(4)E4.

Simulated reduction factor for tritium is 2.5E4.

Differences from initial design are due to geometry modifications.

Abstract

The gas-flow reduction factor of the second forward Differential Pumping Section (DPS2-F) for the KATRIN experiment was determined using a dedicated vacuum-measurement setup and by detailed molecular-flow simulation of the DPS2-F beam tube and of the measurement apparatus. In the measurement, non-radioactive test gases deuterium, helium, neon, argon and krypton were used, the input gas flow was provided by a commercial mass-flow controller, and the output flow was measured using a residual gas analyzer, in order to distinguish it from the outgassing background. The measured reduction factor with the empty beam tube at room temperature for gases with mass 4 is 1.8(4)E4, which is in excellent agreement with the simulated value of 1.6E4. The simulated reduction factor for tritium, based on the interpolated value for the capture factor at the turbo-molecular pump inlet flange is 2.5E4. The difference with respect to the design value of 1E5 is due to the modifications in the beam tube geometry since the initial design, and can be partly recovered by reduction of the effective beam tube diameter.