Status of the KATRIN experiment with special emphasis on source-related issues

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by  Michael Sturm

XXXI PHYSICS IN COLLISION, Vancouver, BC Canada, August 28 - September 1, 2011
Status of the KATRIN experiment with special emphasis on
source-related issues
MichaelSturmfortheKATRINCollaboration
KarlsruheInstituteofTechnology(KIT),
InstituteforTechnicalPhysics,
TritiumLaboratoryKarlsruhe(ITEP-TLK)
The Karlsruhe Tritium Neutrino experiment KATRIN will allow a model independent measurement of the
neutrino mass scale with an expected sensitivity of 0.2 eV/c2 (90% C.L.) and so will help to clarify the role
of neutrinos in the early universe. KATRIN investigates spectroscopically the electron spectrum from tritium
β-decay3H→3He+e− +ν¯e closetothekinematicendpointof18.6keVwithahighresolutionelectro-static
filterofunprecedentedenergyresolutionof∆E=0.93eV[1]. KATRINwillbebuiltattheTritiumLaboratory
KarlsruheonsiteoftheKITCampusNorth.
2
1
0
2 1. Introduction the transmitted β-decay electrons. Both spectrom-
eters are of the MAC-E-Filter (Magnetic Adiabatic
n
a Thepropertiesofneutrinosandespeciallytheirrest Collimation followed by Electrostatic Filter) [4], [5]
J mass play an important role at the intersections of type.

6 cosmology, particle physics and astroparticle physics. The following subsections address the details of
2 Instandardcosmologicalmodels,ouruniverseisfilled somekeycomponentsrelatedtothesourceandtrans-
with primordial neutrinos arising from freeze-out in port section and their present status.
]
x the early universe. These neutrinos are natural can-
e didates for non-baryonic hot dark matter [2].
2.1. Windowless Gaseous Tritium Source
- A model-independent approach to determine the
p
neutrino mass is the kinematical analysis of electrons
e One of the key parameters of KATRIN is the sta-
h fromradioactiveβ-decayneartheendpointenergyE
0 bility of the source on 0.1% level. Figure 2 shows the
[ [3]. A non-vanishing neutrino mass reduces the elec-
principle of KATRIN’s Windowless Gaseous Tritium
tron endpoint energy and distorts the shape of the
3 Source(WGTS).Atthecenterofthebeamtubemolec-
electron spectrum.
v ular tritium gas will be injected continuously. After
3
injection the T molecules will diffuse to both ends
7 2
of the WGTS beam-tube, where most of the tritium
7
2. The KATRIN experiment will be pumped out continuously by turbomolecular
4
. pumps (TMP) in the first stages of the differential
1
Aschemeofthe70mlongKATRINsetupisshown pumping section (DPS1), processed and reinjected.
1
infigure1. KATRINusesastrongwindowlessgaseous The density profile of the gas inside the 10 m long
1
1 tritiumsourceofalmostpuremoleculartritium(95%) beam-tube has to be kept stable on the 0.1% level.
: with a throughput of 40 g tritium per day stabilized Maintaining the required stable injection rate is pro-
v
on 0.1% level. The decay electrons are guided adia- videdbytheInnerLoopSystemdiscussedinthenext
i
X batically from the source through a transport section section. In addition the temperature of the source
r tothespectrometersystembymeansofsuperconduct- beamtube has to be stabilized as well. Maintaining
a ing magnets while at the same time the tritium flow these conditions is a very challenging task.
rate to the spectrometers has to be reduced by a fac- To stabilize the beam tube temperature with a sta-
tor > 1014, since the background rate generated by bility of 0.1% at a setpoint of about 30 K, two copper
tritium decay within the spectrometers has to be less tubes are braced on the source beamtube which di-
than 10−3 counts/s in order to reach the sensitivity rectlycouplethebeamtubetoatwophaseNeonther-
KATRIN is aiming for. The transport section con- mosiphon[11]. Thiscoolingconceptiscurrentlybeing
sists of a differential pumping section (DPS2-F) and tested at the WGTS demonstrator, a partly assem-
a cryogenic pumping section (CPS). In the DPS2-F bledversionofthelaterWGTScryostatwhichhouses
the tritium flow will be reduced by differential pump- thelaterbeam-tubeandcryogenicsbutnotthesuper-
ing while in the CPS tritium will be adsorbed on a conductingmagnets. Afterfinishingthedemonstrator
pre-condensed argon layer prepared inside KATRIN’s teststheWGTScryostatwillbecompletedinorderto
beamtube. Inadditiontothelowbackgroundanhigh be ready for implementation into the KATRIN beam
energyresolutionaswellashighstatisticsareaneces- line.
sity. Atandemspectrometersystemisusedforenergy With the first measurements a temperature stabi-
analysis, followed by a detector-system for counting lization in the milli-Kelvin range has been achieved,
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XXXI PHYSICS IN COLLISION, Vancouver, BC Canada, August 28 - September 1, 2011
Transport section
Detector
Spectrometer
Source DPS2-F CPS
Located in Tritium Laboratory Karlsruhe
Figure 1: Overview of the KATRIN main beam-line. High purity T gas is being injected in the middle of the source
2
tube with a flow rate of 1.8 mbar l/s (40 g(T )/day). Electrons from β-decay leave the source and are guided by
2
magnetic fields through the transport section, while the remaining gas is being removed by active and cryogenic
pumping. The pre-spectrometer filters out the low-energy part of the spectrum, thus only electrons close to the
endpoint region can enter the main spectrometer for the precise energy analysis. Transmitted electrons are then
detected by a low background Si-PIN detector system.
Pressure
T2 Buffer Laser controlled
Raman
vessel buffer
cell
vessel
L e
cn
Impurities rotaem pΔ atcudnoC
reP
Pump
Figure 2: Principle of KATRIN’s Windowless Gaseous Source
Tritium Source.
Figure 3: Simpilfied flow diagram of the Inner Loop
System.
an improvement of a factor of 10 to 20 with regard to
the specification.
KATRIN’sinjectioncapillaryandsourcetube[6]. Be-
ing designed for a stability of 10−3, these test runs
2.2. Inner Loop System showed that the loop system reaches a 2·10−4 stabil-
ity level during 4 week of continuous gas circulation.
Inordertokeepthepressureprofilestableitisnec-
essarytoinjectthetritiumgaswithastabilityof0.1%,
concerning flow-rate and composition. This challeng-
ingtaskisperformedbytheInnerLoopSystem,illus- 2.3. Laser Raman Spectroscopy
tratedinasimplifiedflowdiagraminfigure3. Tritium
isbeinginjectedfromapressurecontrolledbufferves-
sel over a capillary with constant conductivity in the Any small change of the tritium gas composition
middleofthesourcebeamtube. Thegaspumpedout will manifest itself in non-negligible effects on the
bytheTMPsgetspumpedthroughapalladiummem- KATRIN measurements; therefore, precise methods
branefilter(permeator)inabuffervessel. Fromthere to specifically monitor the gas composition have to
the gas is led over a Laser Raman sampling cell and be implemented. Laser Raman Spectroscopy is the
a regulating valve back into the pressure controlled method of choice for the monitoring of the gas com-
buffer vessel. At the filter impurities like 3He from position because it is a non-invasive and fast in-line
tritiumdecayandtritiatedmethanes,beinggenerated measurement technique. Laser Raman spectroscopy
due to interactions of tritum with the carbon inside allowstomonitorallhydrogenisotopologues(T ,DT,
2
the stainless steel walls of the system, are being de- D , HT, HD, H ) simultaneously [7]. Before entering
2 2
tached from the gas stream. The amount of gas not theinjectionvesselintheabovedescribedInnerLoop
recirculatedisreplacedbytritiumfromTLK’sIsotope system,thegaspassesaLaserRamancellinwhichthe
Separation System. gas is being analyzed. Measurements on flowing non-
The Inner Loop System has been set up and com- tritiated [8] and tritiated [9] gas samples have been
missioned successfully. The first test-runs have been performed. Alevelofdetectionof3mbarpartialpres-
performed with a capillary of similar conductance as sure in 1 s acquisition time has been achieved [10].
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XXXI PHYSICS IN COLLISION, Vancouver, BC Canada, August 28 - September 1, 2011
2.4. Differential Pumping Section References
The DPS2-F represents the last stage of turbo-
molecular pumping in the transport section. Its re-
duction of the gas-flow in direction of the spectrome-
ters is of high importance to achieve the 14 orders of [1] KATRINCollaboration, KATRIN Design Report
flowratereductionfromgasinjectionpointinWGTS 2004, FZKA report 7090
to the end of the transport section. At the DPS2- [2] S.Hannestad,Neutrinosincosmology,NewJour-
F the gas flow to the spectrometers will be reduced nal of Physics, Vol 6, No. 108, 2004 arXiv:hep-
by 4 differential pumping TMPs by about 5 orders of ph/0404239v1
magnitude. [3] E.W. Otten et al., Neutrino mass limit from tri-
Another item the DPS2-F has to deal with is that tium β-decay, Rep. Prog. Phys 71 (2008) 086201,
in the KATRIN source tube ions and ion clusters arXiv:0909.2104
are being created. An accumulation of ions inside [4] G. Beamson et al., The collimating and magni-
the beamtube would distort the β-spectrum, in ad- fying properties of a superconducting field photo-
ditiontheseionsarenoteffectivelypumpedout,since electron spectrometer, Journal of Physics E: Sci-
they are confined by the magnetic field in a similar entific Instruments 13 (64-66) 1980
way as the electrons. To prevent this, a dipole sys- [5] A. Picard et al., A solenoid retarding spectrome-
tem for ion removal as well as two Fourier-transform- ter with high resolution and transmissin for keV
ion cyclotron resonance (FTICR) [12] ion traps for electrons, Nuclear Instruments and Methods in
ion-concentration monitoring will be installed in the Physics research Section B Volume 63, Issue 3,
beamtube of the DPS2-F. This instrumentation also 1992, pages 345-358
increases the gas-flow reduction factor compared to [6] M. Sturm, Dissertation, 2010, http://digbib.
the bare beamtube by reducing the inner beam-tube ubka.uni-karlsruhe.de/volltexte/1000019355
diameter [13]. Up to now measurements of the reduc- [7] M. Sturm et al., Monitoring of all hydrogen iso-
tion factor with various gases have been performed topologues at tritium laboratory Karlsruhe using
without instrumentation inside the beamtube. The Raman spectroscopy, Laser Physics 20, 2, 493
measuredgas-flowreductionfactorsforthisgeometry (2010)
are in good agreement with simulations [14]. [8] R. J. Lewis et al., Dynamic Raman spectroscopy
of hydrogen isotopomer mixtures in-line at TILO,
Laser Phys. Lett. 5, 7, 522 (2008)
3. Conclusion [9] S. Fischer et al., Monitoring of Tritium pu-
rity during Long-Term Circulation in the KA-
KATRIN has ambitious goals, both in particle TRIN Test Experiment LOOPINO using Laser
physics and in the technical realization of the exper- RamanSpectroscopy,FusionScienceandTechnol-
imental set-up. Currently the spectrometers, the de- ogy, Volume 60, Number 3, October 2011, Pages
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the first gas-flow reduction factor measurements with tium Sample-Analysis, Accountancy or Process-
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manSpectroscopyformonitoringthegascomposition Pages 976-981
has been successfully implemented. The next major [11] S. Grohmann et al., Stability analyses of the
stepstofinalizetheexperimentsetupwillbefinishing beamtubecoolingintheKATRINsourcecryostat,
the manufacturing of the WGTS cryostat and the de- Cryogenics, Volume 49, Issue 8 (2009) 413-420
livery of the CPS. After delivery, installation test of [12] M. Ubieto-Daz et al., A broad-band FT-ICR
all components the experiment will be ready for the Penning trap system for KATRIN, International
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sues 1-3, November-December 2009, Pages 1-5
[13] S.Lukicetal.,Ionsourcefortestsofionbehavior
Acknowledgments in the KATRIN beam line, Rev. Sci. Instrum. 82
(2011), issue 1 (Jan 2011)
The work of the author was supported in part by [14] S. Lukic et al., Measurement of the gas-flow re-
BMBF (05A08PM1) and DFG SFB Transregio 27 duction factor of the KATRIN DPS2-F differen-
Neutrinos and Beyond. tial pumping section, arXiv:1107.0220v1
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