Commissioning of the KATRIN main...

KIT – University of the State of Baden-Württemberg and

National Research Center of the Helmholtz Association

KIT Center Elementary Particle and Astroparticle Physics (KCETA)

Institute for Nuclear Physics (IKP)

www.kit.edu

Commissioning of the KATRIN main spectrometer

Nancy Wandkowsky for the KATRIN Collaboration

NuMass 2013, Milano

KIT – University of the State of Baden-Württemberg and

National Research Center of the Helmholtz Association

KIT Center Elementary Particle and Astroparticle Physics (KCETA)

Institute for Nuclear Physics (IKP)

www.kit.edu

Commissioning of the KATRIN main spectrometer

Nancy Wandkowsky for the KATRIN Collaboration

NuMass 2013, Milano

Introduction

Spectrometer commissioning status

Spectrometer background studies

Summary and Outlook

3 N. Wandkowsky - Commissioning of the KATRIN main spectrometer

KATRIN experiment

Introduction

low endpoint β source

high count rate

high energy resolution

low background (<10-2 cps)

mν < 0.2 eV (90% CL)

key requirements:


KATRIN experiment

Introduction

low endpoint β source

high count rate

high energy resolution

low background (<10-2 cps)

mν < 0.2 eV (90% CL)

key requirements:

5


N. Wandkowsky - Commissioning of the KATRIN main spectrometer

adiabatic guidance of electrons by magnetic field

precise energy scan by retarding potential

low background: <10-2 cps

UHV in a huge spectrometer: O(10-11) mbar

Requirements for successful electron energy determination:

6



Major milestones achieved:






air coil installation

7




wire electrode installation






8











9





spectrometer bake-out







Air coil system

without any air coil system

distorted flux tube due to earth magnetic field

central field too weak (desired value: 3·10-4 T)

loss of signal electrons

B = 6 T B = 1·10-4 T

flux tube



Air coil system

with earth magnetic field compensation system (EMCS)

flux tube symmetric around spectrometer axis

central field too weak (desired value: 3·10-4 T)

loss of signal electrons

B = 6 T

EMCS

B = 1·10-4 T



Air coil system

with EMCS and low field correction system (LFCS)

central field at desired value: 3·10-4 T

full transmission

B = 6 T

EMCS LFCS

B = 3·10-4 T



Air coil system

with EMCS and low field correction system (LFCS)

central field at desired value: 3·10-4 T

full transmission & background suppression (factor 1000)

B = 6 T

e

EMCS LFCS

B = 3·10-4 T

14



K. Valerius et al., Particle and Nuclear

Physics, Volume 64, Issue 2, April 2010

M. Prall, PHD thesis, Münster, 2011

250 modules, > 24000 wires

precision requirement 0.2 mm

compatible to UHV

Wire electrode

15



Wire electrode

electron energy analysis background suppression

U0

U1

U2

single layer: factor ~10

double layer: factor 100

smooth electric potential

maximal potential in center

16

Wire Electrode – completed (Jan. 2012)

Closing the vessel:

- back at vacuum in July 2012

- p ≈ 10-8 mbar

Th. Thümmler




Spectrometer bake-out: motivation

minimize scattering on residual gas

UHV in a huge spectrometer (1240 m3): O(10-11) mbar






removal of water adsorbed on spectrometer surface

turbomolecular

pump

inner surface: 690 m²






removal of water adsorbed on spectrometer surface

activation of chemical pump (non-evaporable getter St707)



Spectrometer bake-out: procedure

slow heating/cooling (~1°C/h): expansion of vessel and electrode

temperature breakpoints: 200°C – water removal from vessel

300°C – activation of getter material

1,E-11

1,E-10

1,E-09

1,E-08

1,E-07

1,E-06

1,E-05

1,E-04

0

50

100

150

200

250

300

350

350 450 550 650 750 850 950

pre

ssu

re i

n m

bar

tem

pera

ture

in

°C

time in hours

Baking cycle (4. - 30.1.2013)

temperature

pressure

leak developed

pressure back to

10-11 mbar level




0

50

100

150

200

250

300

350




fix point

expansion

insulator

movable point




J. Wolf

0

50

100

150

200

250

300

350

insulator






mm precision positioning

UHV compatibility

voltages successfully applied

no wires damaged

getter only partly activated

vacuum: 9·10-11 mbar

earth field compensated

full flexibility of field shaping




transmission of ß-electrons:

magnetic guiding &

electrostatic retardation

B [T]

e

e e

q [°]

trapping of electrons:

spectrometer acts as

a magnetic bottle,

long storage (h)

Commissioning measurements:



getter material contains radon progenitors

huge getter surface (porous material)

radon (noble gas) escapes into spectrometer volume

Stored electrons: source



Rn-219 half-life: 3.92 s

pump-out time: ~ 360 s

radon undergoes α-decay in the spectrometer volume

Eα = 6.8 MeV

recoiling Po and α absorbed at spectrometer wall

Stored electrons: source



radon undergoes α-decay in the spectrometer volume

electrons are created by: shake-off, internal conversion, Auger effect

implementation of model into simulation software KASSIOPEIA

Stored electrons: background model



F. Fränkle et al, Astropart. Phys. 35, 128 (2011), arXiv:1103.6238

F. Fränkle, PhD thesis at KIT (2010)

S. Mertens et al, Astropart. Phys. 41, 52 (2013) , arXiv:1204.6213

S. Mertens, PhD thesis at KIT (2012)

stored electrons scatter off residual gas → ionization → secondary electrons

high primary energies → thousands of secondary electrons

ring pattern on detector

Stored electrons: background model

pre-spectrometer



calculations for expected

rate of radon decays

@ main spectrometer

model for electron

emission in α-decay

Stored electrons: expectations for main spectrometer



Monte Carlo results: 6·10-2 cps expected, non-poissonian distribution

sensitivity reduction by a factor ~ 2

S. Mertens et al, Astropart. Phys. 41, 52 (2013)

S. Mertens, PhD thesis at KIT (2012)

Stored electrons: influence on neutrino mass sensitivity

design value



electric dipole Electron Cyclotron Resonance

sensitivity reduction not acceptable

active background reduction methods needed

Stored electrons: reduction methods

magnetic pulse



electric dipole cryo-baffle

sensitivity reduction not acceptable

active and passive background reduction methods needed




B

E

vdrift

vdrift

vdrift

vdrift

e-

𝑣 =𝑐

𝐵2 ∙ 𝐸 ⨯ 𝐵

100 V/m → radial drift of electron

electron drifted onto the spectrometer wall

Stored electrons: electric dipole



NEG-Pump

LN2 cooled

baffle

spectrometer

vessel

219Rn

Stored electrons: cryo-baffle





magnetic pulse cryo-baffle

40 N. Wandkowsky - Commissioning of the KATRIN experiment

Summary and Outlook

KATRIN: determination of mν <0.2 eV (90% CL)

Successful wire electrode and air coil installation

Successful bake-out of spectrometer

ToDo: attach detector system

Commissioning measurements for >1 year

Electron transmission

Background:

Cosmic muon induced

Radon induced

Passive & active background reduction methods

Prepare main spectrometer for tritium measurements

41

Thanks for your attention!

Commissioning of the KATRIN main...

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