An angular defined pulsed UV LED photoelectron source for KATRIN

Transcription

1 An angular defined pulsed UV LED photoelectron source for KATRIN Karen Hugenberg1, Stephan Bauer1, H. Baumeister1, Marcus Beck1, Jochen Bonn2, Hendrik Hein1, Hans Werner Ortjohann1, Stephan Rosendahl1, Sebastian Streubel1, Kathrin Valerius1, Christian Weinheimer1, Miroslav Zboril1,3 1 Universität Münster 2 Universität Mainz 3 Rez Prag

2 Outline Introduction Test sources for the KATRIN experiment An angular defined pulsed UV LED photoelectron source simulations Test measurements at the Mainzer neutrino mass experiment

3 The MAC E filter I: Basic Principle A. Picard et al., Nucl. Instr. Meth. B 63 (1992) 0 U 0 energy filter with electric field: only e with E > qu transmitted (high pass) e guided adiabaticaly along magnetic field lines adiabaticity: μ = E / B = const. E E inhomog. magnetic field energy resolution E / E = Bmin/Bmax starting angle between magnetic field and motion determines residual energy in analysing plane

4 The MAC E filter III: The transmission function angle at pinch magnet 0 starting angle 90.0 transmission function for monoenergetic isotropic source E = 0.93 ev

5 The MAC E filter IV: The transmission function transmission function for monoenergetic (dashed: =0.1eV) source with single angle =0o angle at pinch magnet 0 starting angle 90.0 transmission function for monoenergetic (dashed: =0.1eV) source with single angle =40o

6 The real MAC E filter I Problem: no homogeneous magnetic and electric fields over a 10 m diameter: U 1.1 V B/B 10 % transmission function for whole detector / single ring segmented detector position resolution (148 pixel)

7 The real MAC E filter II highest impact on electrons with large starting angles nominal analysing plane virtual analysing plane spectrometer entrance z position [m] time of flight [micro s] analysing plane long. kin. energy E [ev] wire electrode tof 15 µs spectrometer entrance spectrometer exit J. Bonn et al., NIM A 421 (1999) 256

8 Testing a MAC E filter A wish list: stable energy with narrow energy spread point like spot of emission with x y movement calibration monitoring 83m Kr sources position dependence of transmission function well defined angular emission characteristics isotropic mimicking T2 source angular selective probing outer radii pulsed TOF measurements

9 Time of flight measurements E/E 10 5 U = 18 kv B energy 0 ev 0.15 ev 0.20 ev 0.25 ev monoenergetic ( =0.2eV) pulsed (200ns) photoelectron source tested at Mainz K. Valerius et al., New J. Phys. 11 (2009) ns pulse duration

10 The principle of the pre spectrometer e gun starting radius defines starting angle! diploma thesis K. Hugenberg simulation Troitsk and KIT

11 New concepts based on the idea E B strong acceleration in direction of E increase of B in longitudinal direction 90o phd thesis K. Valerius diploma thesis H. Hein 0o Espec = 1.55 ev successfully tested at the Mainz spectrometer see forthcoming publication

12 New approach 1. acceleration along the electric field 2. guidance along the magnetic field lines angle between E and B field determines starting angle B E optical fibres U2 U1 movable UV LED U E B = (E,B) defines starting angle

13 Simulation: Choosing parameters Utotal = 18.6kV 15.6kV

14 Technical drawing rotation axis UV LED light by fibre B spectrometer turnable plate capacitor

15 The setup at Mainz entrance magnet egun position spectrometer

16 Transmission functions for different Efields at start at pinch

17 Transmission functions for different at start at pinch constant potential U = 3 kv

18 TOF µ s, arbitary offset] time of flight [ slow large starting angle small starting angle fast U (V)

19 Summary & outlook sources with special properties needed for KATRIN our angular defined pulsed UV LED egun has been tested intensively at Mainz and provides the following differential properties: energy ( =0.2eV, could be improved easily) position resolution x and y (by transversal B field or mechanically) angle ( 1o) pulsed (e.g. t=200ns) angular defined pulsed photoelectron source at KATRIN:

20 Comparing simulations and measurement measured points PRELIMINARY open parameter: magnetic field at egun position

21 Simulations transversal ^ energy = starting angle determined by angle between E and B additional parameter: acceleration potential KATRIN simulation code by Ferenc Glück et al.

22 Additional features needed: Photoelektronenerzeugung mit UV LED Kalibrations Elektronenquellen (E 18 kev) für Transmissionsfunktionsstudien benötigt Standard Quelle: Konversionselektronen aus 83mKr (17.8 kev, = 2.7 ev) unverzichtbar als natürliche, stabile Energiereferenz Weitere Möglichkeit: Photoelektronen aus UV Bestrahlung einer Edelstahlplatte UV LED: Poptical 400 W (150 µw) central = 265 nm (255 nm) Ecentral = 4.68 ev (4.82 ev) FWHM 0.25 ev 15 nm Seoul Optodevice T9B26C, T9B25C schnelle, kurze Pulse durch Modulation der Diodenspannung: typisch Pulslänge = 40 ns µs Frequenz f = 1 khz 10 khz Edelstahl = (4.4 ± 0.2) ev Anpassung von Austrittsarbeit und UV Energie E ermöglicht prinzipiell noch schärfere Energieverteilung der Photoelektronen