No abstract available

[en] In the paper the ionization state of molecular tritium and electric potentials in a Windowless Gas Tritium Source (WGTS) of tritium β-decay experiment KATRIN are considered. The ionization processes in WGTS are sustained by β-electrons and so-called 'secondary electrons', arising from inelastic and ionization collisions of 'primary' β-electrons with tritium molecules. As a result in the WGTS tritium gas volume acts as a low-temperature and slightly ionized gas steady state close to quasi neutrality (the Debye length is small in comparison with the setup characteristical sizes). On the basis of an one-dimensional self-consistent model the WGTS plasma steady state is described and the influence of plasma phenomena on neutrino mass measuring process is discussed. It is found that electric potentials in a main plasma volume can not significantly make worse the measurement process. At the same time the nonequilibrium electron spectrum and fast plasma flow at the end of the tube can result in instabilities which are able to spoil slightly the β-electron spectrum endpoint. This problem must be carefully investigated further. For more reliable conclusions more detailed consideration is required that will include kinetic effects in the WGTS plasma

[en] The paper treats recent experiments measuring the endpoint region of tritium β-decay with high resolution, sensitivity and background rejection, using an electrostatic filter with adiabatic magnetic collimation. The spectra are analysed with respect to the neutrino mass. These results form the primary source for the present upper limit of the neutrino mass m_ν < 2 eV quoted by the particle data group. Particular attention is paid to the decisive influence which atomic and molecular physics effects take on the results. A brief outlook on future experiments is given.

[en] Applications of hyperpolarized ³He exist in fundamental research as well as in medical studies. Since a decade ³He is polarized in a central facility, located at the University of Mainz and shipped to the users. The gas is polarized via metastability exchange optical pumping (MEOP) at a pressure of approximately 1 mbar inside a magnetic field of 1 mT. The process requires a magnetic field with a relative gradient of Δ B/B < 3.8.10^-4 cm^-1. To construct a compact facility for local gas-polarization it is imperative to create a sufficiently homogeneous magnetic field all over a solenoid's volume in order to be able to use its complete volume for the MEOP assembly. Our concept of a spacious homogenization of a solenoid's magnetic field consists of enclosing it into a shielding of soft magnetic material, providing a high magnetic permeability. In addition to the homogenization of the magnetic field a new concept for the optics, used for the optical pumping has been developed, to fit into the new compact facility. The design of the compact apparatus aims to reach a flux of hyperpolarized ³He at P > 65% of several standard liters per hour. First experimental results, gained from the new compact polarizing apparatus, are presented.

[en] The KATRIN-Collaboration at KIT-Karlsruhe is setting up a huge electrostatic spectrometer in order to search for the absolute value of the neutrino mass from the beta-spectrum of molecular tritium with a sensitivity limit of 0.2 eV. Apart from high intensity, high resolution and low background, this goal requires control of the 18.6 kV filter potential on the ppm level. The paper starts with discussing the impact of uncertainties of beta-endpoint, energy loss and filter potential on the uncertainty of the neutrino mass. Then it describes the various measures for controlling the applied high voltage as well as the potential distribution within the spectrometer and the gaseous tritium source

[en] Since a decade hyperpolarized ³He, used in fundamental research as well as in medical imaging, is polarized in a central facility, located at the University of Mainz and shipped to the users. The gas is polarized via metastability exchange optical pumping (MEOP) at a pressure of approximately 1 mbar inside a magnetic field of 1 mT. At these parameters the process requires the magnetic field to have a relative gradient of ΔB/B<3.8.10^-4 cm^-1. To construct a compact facility for local gas-polarization it is imperative to create a sufficiently homogeneous magnetic field all over a solenoid's volume in order to be able to use its complete volume for the MEOP assembly. Our concept of a spacious homogenization of a solenoid's magnetic field consists of enclosing it into a shielding of soft magnetic material, providing a high magnetic permeability. In addition to the homogenization of the magnetic field a new concept for the optics, used for the optical pumping has been developed, to fit into the new compact facility. Compared to the currently used facility, a neat linear motor replaces the cumbersome hydraulical drive of the piston, which compresses the gas without polarization-losses from 1 mbar up to 5 bar. The design of the compact apparatus aims to reach a flux of hyperpolarized ³He at P>65% of several standard liters per hour.

[en] The method of polarizing ³He via metastability exchange optical pumping is well known since the early 1960s. Since then hyperpolarized gases have found manifold applications in fundamental science as well as in medical research. The present polarizer apparatus in Mainz used as central facility is well established and can produce up to three standard liters of gas per hour with a polarization of 60-65 %, sufficient for medical applications. For basic research where higher degrees of polarization are needed one can reach up to 78 % at a production rate of one standard liter per hour. To provide the users with high polarization degrees and big amounts of polarized gas a compact apparatus was designed. Using this compact polarizer as local polarizing facility enables the users to avoid polarization losses during shipping. For the new polarizer several concepts had to be developed to minimize the size while retaining the production rate and polarization degree. There have been efforts in optimizing optics, polarization conserving compression of the gas and homogenization of the magnetic field. By using a closed cylinder of soft magnetic material a relative field gradient of better than ΔB/B<3.8.10^-4 cm^-1 has been obtained, which is needed to have the desired gradient relaxation time for sufficient polarization. Further results are presented in this talk.

[en] The standard model of the electroweak interaction is tested with ever increasing precision by non-accelerator experiments, e.g. using beta decay. The precision of these experiments has reached a point where the variation of the work function of the materials used for electrodes starts to limit the sensitivity. We investigate these variations of the work function for the aSPECT and the KATRIN experiments using a scanning Kelvin probe and the photoelectric effect. In 2013 aSPECT had a successfull beam time at the cold neutron beam line PF1b at the Institut Laue Langevin to determine the ratio of the weak coupling constants g_A/g_V. KATRIN is being set-up at the Karlsruhe Institute for Technology to measure the absolute mass of the electron-antineutrino. In order to achieve the sensitivity goals of these experiments the variation of the work function of their electrodes in time and space have to be known at the level of 10 meV. Systematic studies of the work function of various surfaces covered with a thin gold layer are presented.

[en] For a wide range of high-precision experiments in physics, well-defined electric potentials for achieving high measurement accuracies are required. An accurate determination of the electric potential is crucial for the measurement of the neutrino mass (KATRIN) as well as the measurement of the e"- anti ν_e correlation coefficient a in free neutron decay (aSPECT). Work function fluctuations on the electrodes lead to uncertainties in the distribution of the electric potential. For aSPECT, the electric potential has to be known at an accuracy of 10 mV. However, due to the patch effect of gold, work function fluctuations of several 100 meV can occur. Therefore, the work function distributions of the gold-plated electrodes have been measured using a Kelvin probe. Furthermore, the change of work function distributions over time as well as the influence of relative humidity on the work function measurement have been investigated. For aSPECT, the work function distributions of the gold-plated electrodes have been measured using a Kelvin probe. Due to the patch effect of gold, work function fluctuations of up to 160 meV occur. This would lead to a significant uncertainty of the potential barrier, which should be known at an accuracy of 10 mV. Furthermore, the change of work function distributions over time as well as the influence of relative humidity on the work function measurement have been investigated.

No abstract available