Commissioning of the vacuum system of the KATRIN Main Spectrometer

Abstract

The KATRIN experiment will probe the neutrino mass by measuring the β-electron energy spectrum near the endpoint of tritium β-decay. An integral energy analysis will be performed by an electro-static spectrometer ("Main Spectrometer"), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m 3 , and a complex inner electrode system with about 120 000 individual parts. The strong magnetic field that guides the β-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. A system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter strips has been deployed and was tested during the commissioning of the spectrometer. In this paper the configuration, the commissioning with bake-out at 300 • C, and the performance of this system are presented in detail. The vacuum system has to maintain a pressure in the 10 −11 mbar range. It is demonstrated that the performance of the system is already close to these stringent functional requirements for the KATRIN experiment, which will start at the end of 2016.

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

“…The β-electrons are guided through the entire beamline by a magnetic field [33] into the pre-spectrometer (d), which acts as a pre-filter that blocks the low-energy electrons of the β-spectrum [34]. The energy analysis around the endpoint region takes place in the main spectrometer (e), which is operated under ultrahigh vacuum conditions [35] at a retarding voltage of about −18.6 kV. Both spectrometers are designed as MAC-E filters, and the main spectrometer achieves a very narrow filter width ( 1 eV) [9] while providing high luminosity for the β-electrons.…”

Gamma-induced background in the KATRIN main spectrometer

“…During standard KATRIN operation, the retarding voltage U 0 applied to the MS hull will be varied systematically around -18.6 kV in order to analyze electrons with energies close to the tritium endpoint energy. To prevent scattering with residual gas, the MS is designed to operate under ultra-high vacuum conditions, with a pressure close to 10 −11 mbar [15].…”

“…Of particular concern is the generation of "truesecondary" electrons, which are defined to have energies below 50 eV [21]. The inner surface of the MS provides a large area for electron emission: 690 m 2 for the steel hull and 532 m 2 for the wire electrode system (although the effective surface area for emission from the latter is reduced due to the two-layer structure of the IE) [15]. Due to imperfections in the magnetic and electrostatic shielding, secondary electrons emitted from these surfaces may have a small probability to enter the sensitive magnetic flux tube that connects to the FPD.…”

Electric Potential and Field Calculation of Charged Bem Triangles and Rectangles by Gaussian Cubature

“…For further details about this spectrometer we refer to Ref. [18]. The dipole electrode model discretizations are explained in detail in Ref.…”

“…A special kind of electron and ion energy spectroscopy is realized by the MAC-E filter spectrometers, where the integral energy spectrum is measured by the combination of electrostatic retardation and magnetic adiabatic collimation. Examples are the Mainz and Troitsk electron spectrometers [13,14], the aSPECT proton spectrometer [15], and the KATRIN pre-and main electron spectrometers [16][17][18]. High accuracy electric field and potential computations are indispensable for precise and reliable charged particle tracking calculations for these experiments.…”