The Windowless Gaseous Tritium Source of KATRIN

Transcription

1 The Windowless Gaseous Tritium Source of KATRIN W. Käfer, for the KATRIN Collaboration Karlsruhe Institute of Technology International School for Nuclear Physics: Neutrinos in Astro- Particle- and Nuclear Physics

2 Outline Why is the WGTS important? What processes do we have to understand? How do experimental conditions and theoretical calculations affect the KATRIN spectrum?

3 KATRIN Overview Karlsruhe Tritium Neutrino experiment Transport sections DPS, CPS Rear section Tritium source WGTS (Windowless Gaseous Tritium Source) Differential β Spectrum 70 m Pre and main spectrometer (both are MAC-E filters) Rate/bin [Hz] Electron detector Integrated β Spectrum U [V]

4 Functional description of the WGTS Purpose: Delivery of β decay electrons per second Requirements 10m Stability of T 2 density profile of 10-3 = ƒ (injection rate, purity, beamtube temperature, pump rate) 90mm Beamtube Length: Diameter: Temperature: 10 m 90 mm 30 K For inner 9.5 m of beamtube Temperature homogeneity: ±30 mk Temperature stability: ±30 mk h -1 Tritium injection Flow rate: mbar l s -1 Pressure: mbar

5 systematic errors (Katrin design report) Source of systematic shift Systematic shift σ syst (m ν 2)[10-3 ev 2 ] Final State Distributions <6 Unfolding energy loss < 2 function/determination of f res ρd monitoring < HV variations <5 Magnetic field variations in <2 WGTS Understanding the WGTS is crucial!!!

6 WGTS Model Experimental Input Temperature Readings Pressure Readings T 2 Purity (Laser Raman) Hall Probes Theoretical Input Scattering cross sections Final States Radiative corrections Synchrotron radiation Auxiliary Models e.g. gas dynamics WGTS Model Intermediate results Density distribution Scattering probabilities Velocity distribution Magnetic field TODAY (simple) spectrometer model β - Spectrum, taking into account experimental conditions and theoretical modifications

7 WGTS Model Experimental Input Temperature Readings Pressure Readings T 2 Purity (Laser Raman) Hall Probes Theoretical Input Scattering cross sections Final States Radiative corrections Synchrotron radiation Auxiliary Models e.g. gas dynamics WGTS Model Intermediate results Density distribution Scattering probabilities Velocity distribution Magnetic field (simple) spectrometer model β - Spectrum, taking into account experimental conditions and theoretical modifications

8 WGTS gas dynamics Input: Temperature-Profile Inlet/Outlet Pressure Output: density + velocity profile Different flow regimes solve Boltzmann equation Numerical code F. Sharipov et al. (Univ. Parana) n [cm -3 ] 0 5 z[m] T2 injection T2 pumping z [m]

9 First Look at Radial dependency 2 phase Ne tube

10 Velocity profile Doppler Effect Maxwell Boltzmann distribution + bulk velocity U z r r f (, v) exp v 3 + v 2 2 n( z) r ϕ z ( ) 2 π v v u 0 + ( v U ) z 2 Thermal velocity ~ 288 m/s Bulk velocity ~ m/s T 2 e - example: electron energy: ev (endpoint) T 2 velocity: 288 m/s Energy shift for parallel emission: ΔE = 129 mev Bulk velocity [m/s] r/r at different z positions

11 WGTS Model Experimental Input Temperature Readings Pressure Readings T 2 Purity (Laser Raman) Hall Probes Theoretical Input Scattering cross sections Final States Radiative corrections Synchrotron radiation Auxiliary Models e.g. gas dynamics WGTS Model Intermediate results Density distribution Scattering probabilities Velocity distribution Magnetic field (simple) spectrometer model β - Spectrum, taking into account experimental conditions and theoretical modifications

12 WGTS model: Principle Transmission probability Differential β Spectrum E [ev] integrated β Spectrum (Endpoint) dn = 2 2 N ( qu, E, m ) R( E, qu) ( E, E, m ) de 0 ν 0 ν de = Rate/bin [Hz] U [V]

13 3D WGTS model First WGTS model: only integrated properties considered refined WGTS model (3-dimensional) to include inhomogeneities With detailed distributions: Create voxelized β spectra Radial pixels: detector layout WGTS tube Tritium injection e - to spectrometer 10 m

14 Calculation of the β Spectrum Transmission probability Response functions for 10 bins bin at front end bin at rear end Differential β Spectrum E [ev] integrated β Spectrum (Endpoint) Rate/bin [Hz] WGTS tube To detector U [V]

15 WGTS Model Experimental Input Temperature Readings Pressure Readings T 2 Purity (Laser Raman) Hall Probes Theoretical Input Scattering cross sections Final States Radiative corrections Synchrotron radiation Auxiliary Models e.g. gas dynamics WGTS Model Intermediate results Density distribution Scattering probabilities Velocity distribution Magnetic field (simple) spectrometer model β - Spectrum, taking into account experimental conditions and theoretical modifications

16 Final State Distribution Effect of m ν Daughter molecule ( 3 HeT / 3 HeD) has rotational/vibrational/electronic excitations additional energy loss modified β Spectrum dn de f P Θ ( ) ( ) f E 0 E f E E 0 E f E ( E E E ) 0 f m ν 2 m 2 v Doss/Tennyson

17 Summary & Outlook Understanding the WGTS is important for KATRIN systematics Broad range of physics 3D WGTS model: Calculation of β Spectrum for segments of the WGTS Validation with test experiments and monitoring Next: Demonstrator measurements end of this year

18 Backup

19 Source and transport section (tritium system) T=77 K T=27 K T= 3 K R=10 7 diff. pumping system density tritium source (WGTS) longitudinal density profile R=10 7 T=77 K diff. pumping system (DPS) cryo-pump (CPS) DPS2-R 5% 95% DPS1-R WGTS DPS1-F 1% outer loop inner loop controlled T 2 injection T 2 processing isotope seperation outer loop DPS2-F 95% 5% 1% existing TLK infrastructure CPS every 60 days (<1 Ci) T 2 retention

20 Energy loss of electrons in Tritium For 1 (a) or 2 interactions (b) Aseev et al. Eur. Phys. J. D 10, 39{52 (2000)

21 BT cooling Ne/Ar thermosiphon

22 Neutrino mass and β-decay kinetic measurement of the neutrino mass experimentally observable T 2 : halflife 12.3 a E 0 : ev