[en] An electron antineutrino mass has been measured in tritium β decay in the Troitsk ν-mass experiment. The setup consists of a windowless gaseous tritium source and an electrostatic electron spectrometer. The whole data set acquired from 1994 to 2004 was reanalyzed. A thorough selection of data with the reliable experimental conditions has been performed. We checked every known systematic effect and obtained the following experimental estimate for neutrino mass squared m_ν²=-0.67±2.53 eV². This gives an experimental upper sensitivity limit of m_ν<2.2 eV, 95% C.L. and upper limit estimates m_ν<2.12 eV, 95% C.L. for Bayesian statistics and m_ν<2.05 eV, 95% C.L. for the Feldman and Cousins approach.

[en] The results obtained in the Troitsk nu-mass experiment by measuring the electron-antineutrino mass in tritium beta decay are presented. The facility used consists of a gaseous windowless tritium source and an electrostatic electron spectrometer involving an adiabatic magnetic collimation. Runs in which measurement conditions were reliably established were thoroughly selected in analyzing data obtained from 1994 to 2004. All known systematic effects were taken into account. For the square of the electron-antineutrino mass, the treatment of measured spectra yielded the following result: m_ν² = -0.67 ± 1.89_stat. ± 1.68_syst. eV². The use of the Bayesian method and the Feldman-Cousins unified approach made it possible to obtain the following upper limits on the mass: m_ν < 2.12 eV (at a 95% C.L.; Bayesian method) and m_ν < 2.05 eV (at a 95% C.L., Feldman-Cousins method). At the same time, an estimation of the sensitivity limit without allowance for negative values of the square of the mass leads to m_ν < 2.2 eV (at a 95% C.L.). Measured spectra were analyzed for the possible existence of an additional structure (step) in the electron spectrum near the boundary energy. The conclusion drawn from this analysis was that, within the existing statistical errors, there are no reasons for introducing such a feature.

[en] Results of searches for effects of space-charge accumulation in the gaseous tritium source in the Troitsk neutrino-mass experiment are presented. The broadening and the shift of the L3 line of conversion electrons in a ^83mKr gaseous source circulating together with tritium was investigated. The attained limit on the magnitude of fluctuations of the space-charge potential makes it possible to set a limit on the negative neutrino mass squared in the Troitsk neutrino-mass experiment (−0.8 < Δm_ν² ≤ 0 eV²), a spurious effect associated with this potential. A statistically reliable shift of the position of the L3 line is discovered. This indicates that processes of of space-charge accumulation do indeed proceed in the source at a level that is significant for the future experiment Katrin.

[en] Results of searches for effects of space-charge accumulation in the gaseous tritium source in the Troitsk neutrino-mass experiment are presented. The broadening and the shift of the L3 line of conversion electrons in a ^83mKr gaseous source circulating together with tritium was investigated. The attained limit on the magnitude of fluctuations of the space-charge potential makes it possible to set a limit on the negative neutrino mass squared in the Troitsk neutrino-mass experiment (-0.8 < Δm_ν² ≤ 0 eV²), a spurious effect associated with this potential. A statistically reliable shift of the position of the L3 line is discovered. This indicates that processes of of space-charge accumulation do indeed proceed in the source at a level that is significant for the future experiment Katrin

[en] The Karlsruhe Tritium Neutrino (KATRIN) experiment will determine the mass of the electron neutrino with a sensitivity of 0.2 eV (90% CL) via a measurement of the β-spectrum of gaseous tritium near its endpoint of E₀ = 18.57 keV. An ultra-low background of about b = 10 mHz is among the requirements on reaching this sensitivity. In the KATRIN main beam line, two spectrometers of MAC-E filter type are used in tandem configuration. This setup, however, produces a Penning trap, which could lead to increased background. We have performed test measurements showing that the filter energy of the pre-spectrometer can be reduced by several keV in order to diminish this trap. These measurements were analyzed with the help of a complex computer simulation, modeling multiple electron reflections from both the detector and the photoelectric electron source used in our test setup. (paper)

[en] The KArlsruhe TRItium Neutrino (KATRIN) experiment is a next-generation, large-scale tritium β-decay experiment to determine the neutrino mass by investigating the kinematics of tritium β-decay with a sensitivity of 200 meV/c² using the MAC-E filter technique. In order to reach this sensitivity a low background level of 10⁻² counts per second (cps) is required. A major background concern in MAC-E filters is the presence of Penning traps. A Penning trap is a special configuration of electromagnetic fields that allows the storage of electrically charged particles. This paper describes the mechanism of Penning discharges and the corresponding measurements performed at the test setup of the KATRIN pre-spectrometer. These investigations led to the conclusion that the observed electric breakdown, strong discharges and extremely large background rates were due to discharges caused by Penning traps located at both ends of the pre-spectrometer. Furthermore, the paper describes the design of a new set of electrodes (modified ground electrodes and new ''anti-Penning'' electrodes) to successfully remove these traps. After the installation of these electrodes in the pre-spectrometer, the measurements confirmed that the strong Penning discharges disappeared. The experience gained from the pre-spectrometer was used to design the electrode system of the main spectrometer. Recent measurements with the main spectrometer showed no indications of Penning trap related backgrounds