Joachim Wolf

Outgassing measurements with a prototype for a large UHV spectrometer

The Karlsruhe Tritium Neutrino experiment (KATRIN) is an ambitious experiment to measure the electron neutrino mass from decay electrons of tritium with a sensitivity of 0.2 eV/c2. The length of the setup will be about 70 m, comprising an ultra luminous gaseous tritium source, a transport section with differential pumping, an electrostatic tandem spectrometer and a detector. The spectrometer section consists of two UHV vessels: i) the pre‐spectrometer with a diameter of 1.7 m and a length of 3.4 m acts as a pre‐filter for the large number of electrons entering from the source, ii) the main spectrometer with a length of 23.3 m and a diameter of 10m provides the necessary energy resolution of 1 eV. The high sensitivity requires a very low background rate of about 10 mHz. Among others this rate depends on the pressure inside the spectrometers, which are designed to maintain UHV conditions of 10−11 mbar or below.First prototype measurements with the smaller pre‐spectrometer (volume: 8.5 m3, surface: 25 m2) ha...

Simulation and measurement of the suppression of radon induced background in the KATRIN experiment

Short-lived radon isotopes, such as 219Rn or 220Rn, are a serious source of background for the measurement of the neu-trino mass with the KATRIN experiment. Most of the radon emanates from the main vacuum pumps of the KATRIN Main Spec-trometer, which consist of 2000 m of Non-Evaporable Getter (NEG) strips. This paper describes a method to suppress the radon rate with liquid-nitrogen-cooled baffles in front of the NEG-pumps in the ultra-high vacuum chamber and compares simulations with measured data. The effectiveness of the method depends both on the half-life of the radon isotopes, and on the temperature of the cryogenic baffles, which affects their sojourn time on the cold surface. The measurements with the Main Spectrometer showed that the radon suppression with cold baffles works sufficiently well, so that the remaining background is no longer dominated by radon decays.Short-lived radon isotopes, such as 219Rn or 220Rn, are a serious source of background for the measurement of the neu-trino mass with the KATRIN experiment. Most of the radon emanates from the main vacuum pumps of the KATRIN Main Spec-trometer, which consist of 2000 m of Non-Evaporable Getter (NEG) strips. This paper describes a method to suppress the radon rate with liquid-nitrogen-cooled baffles in front of the NEG-pumps in the ultra-high vacuum chamber and compares simulations with measured data. The effectiveness of the method depends both on the half-life of the radon isotopes, and on the temperature of the cryogenic baffles, which affects their sojourn time on the cold surface. The measurements with the Main Spectrometer showed that the radon suppression with cold baffles works sufficiently well, so that the remaining background is no longer dominated by radon decays.

Absolute neutrino mass measurements

The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass‐squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino‐less double beta decay (0v2β) searches, single β‐decay experiments provide a direct, model‐independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy. Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium β‐experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope ( 137 Rh ) is being pursued by the international MARE collaboration using micro‐calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R&D phase. This paper reviews the present status of neutrino‐mass measurements with cosmological data, 0v2β decay and single β‐decay.