Condensed Krypton Source and inter-spectrometer Penning trap at the KATRIN experiment

Giugno 26, 2019@3:00 pm–4:00 pm
Aula 500

M. Fedkevych, University of Münster, the KATRIN collaboration

The KArlsruhe TRItium Neutrino experiment (KATRIN) is a direct low-background measurement of the neutrino
mass from the kinematics of tritium -decay with an intended sensitivity of 0.2 eV=c2 (90 % C.L.). It uses
a tandem of two electrostatic spectrometers of MAC-E filter type, called pre- and main spectrometers, to analyze
energies of -electrons generated in WGTS (windowless gaseous tritium source). To achieve the sensitivity
goal, background minimization, as well as accurate energy calibration, monitoring and precise determination of
transmission function of the main spectrometer are required.
After an introduction of the current status of the KATRIN experiment I will present two topics of my own
work in more details.
In the first part of my talk, I will report about elimination of one of the important background sources, the
inter-spectrometer Penning trap. The trap is created by the negative retarding potentials of the spectrometers
combined with the magnetic field produced by a common superconducting magnet. Even at the ultra-high
vacuum conditions of KATRIN electrons may get trapped in this Penning trap creating additional background.
They could even produce discharges which may interrupt the data-taking process and damage parts of the
spectrometer and detector section of KATRIN. As a countermeasure, electron catchers were implemented in the
beamline part between the two spectrometers to remove trapped electrons. The system was tested at various
pressure conditions and showed its effectiveness for suppression of the Penning trap effects. In this talk I will
explain details of the measurements and experimental results.
In the second part, I will present the Condensed Krypton calibration Source (CKrS) developed in Münster,
one of the several calibration sources used in KATRIN, which utilizes the nearly monoenergetic conversion
electrons from cryo-adsorbed 83mKr. The CKrS can be used for frequent measurements due to its relative
simplicity; moreover, as a point-like source it allows for per-pixel calibration of KATRIN focal plane detector
(FPD), with comparatively high rates. The cleanliness of the substrate together with quality of frozen radioactive
films being crucial for the stability and reproducibility of the conversion electron spectrum are monitored by
means of laser ellipsometry. The CKrS was installed in 2017 at the KATRIN cryogenic pumping section (CPS).
Here, I will present the characterization measurements with the CKrS at different vacuum conditions (before
and after bake-out of the system) and will discuss analysis and interpretation of the stability, spectroscopy and
ellipsometry data with different krypton films.