Florian Heizmann

Hendrik Seitz-Moskaliuk

null null

Journal of Physics Conference Series

KATRIN Collaboration

Heizmann, Florian

Seitz-Moskaliuk, Hendrik

KITopen

Journal of Physics: Conference SeriesPAPER • OPEN ACCESSThe Windowless Gaseous Tritium Source (WGTS)of the KATRIN experimentTo cite this article: Florian Heizmann et al 2017 J. Phys.: Conf. Ser. 888 012071 View the article online for updates and enhancements.Related contentThe KATRIN experimentMarcus Beck and the Katrin collaboration-KATRIN: an experiment to determine theneutrino massR G H Robertson-Direct neutrino mass determination: Statusand prospectsV M Hannen-This content was downloaded from IP address 129.13.72.197 on 07/11/2017 at 14:511Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd1234567890Neutrino2016 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 888 (2017) 012071  doi :10.1088/1742-6596/888/1/012071The Windowless Gaseous Tritium Source (WGTS) ofthe KATRIN experimentFlorian Heizmann and Hendrik Seitz-Moskaliuk, for the KATRINcollaborationKarlsruhe Institute of Technology, Institute for Experimental Nuclear Physics (IEKP)E-mail: florian.heizmann@kit.edu & hendrik.seitz-moskaliuk@kit.eduAbstract. The Karlsruhe Tritium Neutrino Experiment (KATRIN) will perform a direct,kinematics-based measurement of the neutrino mass with a sensitivity of 200 meV (90 % C. L.),which will be reached after 3 years of measurement time. The neutrino mass is obtained byinvestigating the shape of the energy spectrum of tritium β-decay electrons close to the endpointat 18.6 keV with a spectrometer of MAC-E filter type. This contribution reviews the currentstatus of the tritium source cryostat and magnet system which is currently in its first cool-downphase. Furthermore, the next steps of the comprehensive pre-tritium measurement programmeto characterise the apparatus and investigate important systematics are outlined.This work is supported by BMBF (05A14VK2) and the Helmholtz Association.1. IntroductionFigure 1. Schematic overview of the 70 m KATRIN beamline: (RS) rear section, (WGTS)windowless gaseous tritium source, (DPS) differential-pumping section, (CPS) cryogenic-pumping section, (PS) pre-spectrometer, (MS) main spectrometer, and (FPD) focal-planedetector.KATRIN is currently in its commissioning phase. All major components are on site and will beoperated together for “first light” measurements in October 2016. The full KATRIN beamlineis 70 m long and depicted in Fig. 1. In a circular flow, molecular tritium gas is injected at thecentre of the windowless source tube and pumped out at both ends, providing a constant gascolumn density of 5·1017 cm−2 which is stabilised on the per mille level. About 1010 β-decayelectrons per second leave the windowless gaseous tritium source (WGTS) and are adiabaticallyguided in strong magnetic fields. While the electrons reach the spectrometers, the tritium flux21234567890Neutrino2016 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 888 (2017) 012071  doi :10.1088/1742-6596/888/1/012071is reduced by 14 orders of magnitude by the differential and cryogenic pumping sections (DPSand CPS). The spectrometer of MAC-E filter type analyses the energy of the electrons in finesteps at the endpoint region. Electrons passing the high-pass energy filter are counted by a148-pixel detector. At the rear side of the WGTS, the rear section houses the rear wall and anelectron gun for calibration and monitoring purposes. A detailed description of the KATRINsetup can be found in [1]. This paper focuses on the WGTS. Most of the KATRIN systematicsare linked to this component and this is why a comprehensive commissioning measurementprogramme is planned. Following a description of the WGTS design goals the current statusof the installation, instrumentation and commissioning is reported. Finally, an outlook towardsthe cold pre-tritium measurement phase is given, in which the first quantification of systematicuncertainties is expected.2. Design requirementsFigure 2. Cross-sectional view of theWGTS. The gas density profile inside thebeam tube is shown in green.Figure 3. Temperature behaviour (prelim-inary, uncalibrated) of a PT500 beam tubesensor and a TVO sensor of one magnet.The 16 m long source cryostat weighs 27 t, and houses 7 superconducting magnets with fieldstrengths of 3.6 and 5.6 T. A complex cooling system, comprising several shields and cryogeniccycles, allows operating the inner beam tube (diameter 90 mm) at a stabilised temperature ofabout 30 K. As detailed in the KATRIN design report [1] the WGTS has to fulfill the followingrequirements:• High activity: In order to collect sufficient statistics, KATRIN needs a highly luminoustritium source (for illustration: only a tiny fraction of 2 ·10−13 of all tritium β-decays emitselectrons with energies in a 1 eV interval below the endpoint [1]). The beam tube geometrywith 3.35 µbar inlet pressure at the centre of the cryostat and four turbo molecular pumpsat both ends lead to a column density of 5·1017 cm−2. The resulting effective column densitytaking into account losses in the count rate due to scattering is close to optimum [1]. Adrawing of the source cryostat, illustrating also the gas density profile inside the sourcetube, is depicted in Fig. 2.• High stability: The KATRIN systematics budget tolerates fluctuations of the columndensity on the per mille level only. This requires a per mille level stabilisation of thesource cryostat temperature and of the inlet and outlet pressure. The stability of the sourcetemperature is achieved by two-phase neon cooling at about 30 K [2]. Test measurementsfound the stability to be more than one order of magnitude better than projected [3]. Thestability of the inlet pressure is achieved by a pressure controlled buffer vessel, which alsoexceeded the design goal by one order of magnitude [4].31234567890Neutrino2016 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 888 (2017) 012071  doi :10.1088/1742-6596/888/1/012071• High monitoring precision: Key parameters of the source have to be monitored on the permille level. Besides temperature and pressure, the tritium purity and the β-decay rateare of interest. The tritium purity is monitored by a laser Raman system positioned in theinner tritium loop [5]. The rate is continuously monitored by β-induced X-ray spectrometryvia the rear section and by a forward beam monitor at the location of the CPS, and canfurthermore be checked in regular intervals using the rear section electron gun [6].3. Installation and commissioningThe WGTS apparatus was delivered to KIT in September 2015; installation and set-up of themechanical and cryogenic infrastructure are now complete. About 800 sensors of the cryostathave been tested successfully. A first leak test at room temperature showed an integral leak rateof less than 10−8 mbar l/s. At the beginning of August 2016 the first cool-down of the magnetsand the beam tube started (Fig. 3). The cool-down of the beam tube was done without coolant,relying solely on heat radiation absorbed by the inner shield cooling cycle. At a stabilisedtemperature of 100 K, integral leak tests were performed to confirm a leak rate of less than2 ·10−8 mbar l/s, which is within specifications. Tests of the superconducting magnet system areongoing.4. Upcoming measurement programmeBefore starting with first tritium measurements in summer 2017, a comprehensive and dedicatedmeasurement programme is foreseen for the WGTS in interplay with the other components:• The two-phase neon cooling system of the beam tube will be commissioned to verify thetemperature stability of former test measurements [3]. For October 2016 a “first light”measurement campaign for the whole KATRIN beamline is planned. Electrons and ionsproduced at the rear section will be guided by the magnetic fields of all components to thedetector to verify precision alignment of the overall beamline [7].• In the first half of 2017, a cold pre-tritium measurement campaign with the whole KATRINbeamline at nominal conditions but with deuterium gas circulating in the WGTS will beperformed [7]. The aim is to demonstrate the functionality of all safety installations fortritium operation but also to determine and test some of the major systematic uncertaintiesof the KATRIN experiment, e. g., the test and quantification of the stability of the columndensity and the related parameters and monitoring units as described in Sec. 2, the test ofthe unfolding procedure of the energy loss function of electrons scattering inside the sourcevolume [8], and the test of the WGTS 83mKr mode, in which the WGTS is operated at110 K and 83mKr is added to the normal gas mixture to determine the plasma potentialinside the source [9].References[1] KATRIN Collaboration 2004 FZKA Report 7090[2] Grohmann S 2009 Cryogenics 49 413-420[3] Grohmann S, Bode T, Ho¨tzel M, Scho¨n H, Su¨ßer M and Wahl T 2013 Cryogenics 55-56 5-11[4] Priester F, Sturm M and Bornschein B 2015 Vacuum 116 42-47[5] Fischer S, Sturm M, Schlo¨sser M, Bornschein B, Drexlin G, Priester F, Lewis R J and Telle H H 2011 FusionSci. Technol. 60 925-930[6] Babutzka M, Bahr M, Bonn J, Bornschein B, Dieter A, Drexlin G, Eitel K, Fischer S, Glu¨ck F, GrohmannS, Ho¨tzel M, James T M, Ka¨fer W, Leber M, Monreal B, Priester F, Ro¨llig M, Schlo¨sser M, Schmitt U,Sharipov F, Steidl M, Sturm M, Telle H H and Titov N 2012 New J. Phys. 14 103046[7] Bornschein B, Besserer U, Steidl M, Sturm M, Valerius K and Wendel J 2016 Fusion Sci. Technol.: Tritium2016accepted for publication[8] Hannen V, Valerius K, Weinheimer C and Wolff I 2016, submitted for publication[9] Ve´nos D, Sleza´k M, Dragoun O, Inoyatov A, Lebeda O, Pulec Z, Sentkerestiova´ J and S˘palek A 2014 J. Instrum.9 12010

The Windowless Gaseous Tritium Source (WGTS) of the KATRIN experiment

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The Windowless Gaseous Tritium Source (WGTS) of the KATRIN experiment

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