Abstract
The KATRIN experiment aims to determine the effective electron neutrino mass with a sensitivity of {0.2}{hbox { eV/c}^{2}} (%90 CL) by precision measurement of the shape of the tritium upbeta -spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. A common background source in this setup is the decay of short-lived isotopes, such as {}^{text {219}}text {Rn} and {}^{text {220}}text {Rn}, in the spectrometer volume. Active and passive countermeasures have been implemented and tested at the KATRIN main spectrometer. One of these is the magnetic pulse method, which employs the existing air coil system to reduce the magnetic guiding field in the spectrometer on a short timescale in order to remove low- and high-energy stored electrons. Here we describe the working principle of this method and present results from commissioning measurements at the main spectrometer. Simulations with the particle-tracking software Kassiopeia were carried out to gain a detailed understanding of the electron storage conditions and removal processes.
Highlights
The KArlsruhe TRitium Neutrino experiment KATRIN [1] aims to determine the ‘effective mass’ of the electron neutrino by performing kinematic measurements of tritium β-decay
A major source of radon nuclei in the main spectrometer is the array of non-evaporable getter (NEG) pumps, which are used in combination with turbo-molecular pumps (TMPs) to achieve ultra-high vacuum conditions down to p ≤ 10−10 mbar
In this work we presented the theory, design, and comissioning of a novel background reduction technique at the KATRIN experiment, the so-called magnetic pulse method
Summary
The KArlsruhe TRitium Neutrino experiment KATRIN [1] aims to determine the ‘effective mass’ of the electron neutrino (an incoherent sum over the mass eigenstates [2]) by performing kinematic measurements of tritium β-decay. The integral β-spectrum is measured by varying the retarding potential near the tritium endpoint and counting transmitted electrons at the focal-plane detector (FPD [19]). The retarding potential accelerates these electrons towards the detector, where they reach a kinetic energy close to the tritium endpoint This background is indistinguishable from signal βelectrons, and dedicated countermeasures are needed to reach the KATRIN sensitivity goal. Because the method interferes with the process of the β-spectrum measurement, it should be applied in a reasonably short timescale on the order of a few seconds This is achieved by utilizing the existing air coil system [26] to invert the magnetic guiding field, which forces electrons towards the vessel walls where they are subsequently captured. Kassiopeia, which has been developed by the KATRIN collaboration [28] (Sect. 4)
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