Technical design and commissioning of the KATRIN large-volume air coil system

Abstract

The KATRIN experiment is a next-generation direct neutrino mass experiment with a sensitivity of 0.2 eV (90% C.L.) to the effective mass of the electron neutrino. It measures the tritium β-decay spectrum close to its endpoint with a spectrometer based on the MAC-E filter technique. The β-decay electrons are guided by a magnetic field that operates in the mT range in the central spectrometer volume; it is fine-tuned by a large-volume air coil system surrounding the spectrometer vessel. The purpose of the system is to provide optimal transmission properties for signal electrons and to achieve efficient magnetic shielding against background. In this paper JINST 13 P02003we describe the technical design of the air coil system, including its mechanical and electrical properties. We outline the importance of its versatile operation modes in background investigation and suppression techniques. We compare magnetic field measurements in the inner spectrometer volume during system commissioning with corresponding simulations, which allows to verify the system's functionality in fine-tuning the magnetic field configuration. This is of major importance for a successful neutrino mass measurement at KATRIN.

$$\upbeta $$-Decay spectrum, response function and statistical model for neutrino mass measurements with the KATRIN experiment

“…During the ongoing commissioning measurement campaign of the KATRIN experiment, many aspects of the current response model will be verified with experimental data. The results of recent investigations are described in [38,49,67]. This thorough characterization of the complex setup will allow a quantitative evaluation of the systematic effects in the neutrino mass analysis at KATRIN.…”

“…(22)) is also widened or narrowed. Utilizing a set of magnetic field compensation coils, operated with an optimal current distribution, around the spectrometer vessel, the spread of the radial inhomogeneity of the magnetic field is minimized to a few μ T when an optimized current distribution is applied [37,38]. The resulting variation in the filter width in the analyzing plane due to the magnetic field inhomogeneity is thus reduced to about 10 meV [46].…”

First operation of the KATRIN experiment with tritium

“…We assume uncertainties of the magnetic fields of σ B source = 2.5%, σ B ana = 1% and σ B max = 0.2%. These values are estimated based on comparisons of simulations with the KATRIN software Kassiopeia [47] and measurements with Hall sensors and precision magnetic field sensors [48,49].…”

Technical design and commissioning of a sensor net for fine-meshed measuring of the magnetic field at the KATRIN spectrometer

“…The current leading elements of the EMCS run parallel to the spectrometer walls (blue and red lines as well as orange circles in Figure (a)). A more detailed description can be found in [8]. [10], which moves on the inner side of the LFCS support ring and measures the magnetic field on predefined sampling positions.…”

“…Bottom: In case of an additional global external magnetic field (e.g.earth magnetic field) of By = 50 µT the perturbed field lines intersect with the MS walls. magnetic field shape, large aircoil systems [8,15] are arranged around the MS: The earth magnetic field compensation system (EMCS) for the compensation of the earth magnetic field and the low field coil system (LFCS) for the fine tuning of the magnetic transport flux tube (see Figure 3). The requirements on the magentic field and achieved performances of the magnetic field generating systems are described in more detail in [5].…”