1. John Thornby 4 th April 20071 Development of a Novel Charge Spectrometer IoP Nuclear and Particle Physics Divisional Conference John Thornby University of Warwick

2. John Thornby 4 th April 20072 Overview Motivation for a new technique How it works  Empirical principles  Experimental details  Instrument characterisation  Recent results Review: Applications, Goals and Outlook

3. John Thornby 4 th April 20073 Acknowledgements & Disclaimer Acknowledgements: Dr. Yorck Ramachers, Adrian Lovejoy, Disclaimer: This is not strictly a Nuclear Physics talk!

4. John Thornby 4 th April 20074 Motivation for a new Technique Once upon a time in Warwick… This man had a crazy idea β- endpoint experiment View to perhaps measuring absolute υ mass Borrowing concepts from Mainz & Troitsk BUT Laboratory scale & fraction of budget!

5. John Thornby 4 th April 20075 The Idea… Past experiments basically count electrons Replace with a continuous rate of change observable?

6. John Thornby 4 th April 20076 The Idea Continued β- isotope used as a current source Charges a capacitor (simply a charge collector) Charges converted to Voltages Obtain an integrated β- spectrum VCVC C I source e-e-

7. John Thornby 4 th April 20077 So, how does it work? Process self-quenches: Accrued e - provide increasing retarding potential → Cost and noise-free! Only most energetic e - overcome repulsion Eventually no more electrons will make it… Corresponds to end-point energy. Measure it! 63 Ni e-e- e-e- e-e- e-e- e-e- e-e- SourceCollector e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

8. John Thornby 4 th April 20078 Integrated β- Spectrum Most electrons energies contribute → dV C /dt large Only rare high-energy electrons contribute → dV C /dt small End-point @ dV C /dt = 0

9. John Thornby 4 th April 20079 Now the clever part… Capacitor actually a dipole magnet ball bearing… Magnetically levitated & held ~ 10 -4 mbar vacuum Accrued charge cannot escape!

10. John Thornby 4 th April 200710 Levitating the Ball Magnetic forces balance gravity Unique in-house designed electronics Provides stable, reproducible configuration Levitation coil Permanent Magnets Hall Probe

11. John Thornby 4 th April 200711 Levitation Electronics Ball equilibrium maintained with μW Power!

12. John Thornby 4 th April 200712 Non-Invasive Voltage Measurement – Inverse Kelvin Technique Supply 11 Hz, 1V p-p sine wave to coil AC in levitation coil → field oscillates Ball oscillates up and down above a special pickup plate

13. John Thornby 4 th April 200713 Inverse Kelvin Technique Continued Ball oscillates, capacitance wrt pickup plate changes → induces AC voltage on pickup Amplify the signal and analyze AC output with PSD (Lock-in amplifier)

14. John Thornby 4 th April 200714 Calibration Induced AC voltage on pickup proportional to DC voltage on ball PSD Returns an error voltage Contact potential V ball (V) ~ 0.2 × V PSD (mV)

15. John Thornby 4 th April 200715 Collector Insulation 2mV band Need to know how stable voltage is in order to reliably determine the quench/end point Justified in quoting stability of ±1mV Corresponds to 1meV energy resolution!

16. John Thornby 4 th April 200716 Charging the Ball in vacuum Can we charge the ball in vacuum?  β /conversion electron isotopes  Stimulated emission electrons

17. John Thornby 4 th April 200717 Plan “B” – Stimulated Emission Sharp needle at a large –ve potential At ~ 1.5 kV electrons are emitted Detected on the ball! ~ 1.5 kV Tungsten needle, atomically sharp e-e- Ball ~ 1.5 cm

18. John Thornby 4 th April 200718 Electron Collection Demonstration ΔV 0 = 0.903 V ΔV 1 = 0.030 V ΔV 2 = 0.315 V ΔV 3 = 0.561 V ΔV 0 = ΔV 1 + ΔV 2 + ΔV 3 Offset consistent with genuinely charging the ball 1.5 kV 1.75 kV 2.0 kV 0 V 250 V increments, every 5 minutes

19. John Thornby 4 th April 200719 Air Conductivity Measurement Capacitors can be discharged too… Low voltages are well-fit by exponential Not so good for higher voltages Physics to be investigated here Need to measure Capacitance, since exponential decay constant is f(C,R) Ball Voltage vs. Time

20. John Thornby 4 th April 200720 Review and “to do” list… Collector insulation and charging under vacuum has been demonstrated Next step is to use a real source in vacuum Calibrate HT controller  109 Cd, mono-energetic particles as a reference Measure Capacitance of ball to pickup plate (non-trivial) → Measure Air conductivity Perform tests in a variety of configurations

21. John Thornby 4 th April 200721 Outlook & Potential Applications Exciting New Experiment – prototype stage  β- endpoint measurements → υ mass  Possible sensitivity to neutrino mass hierarchy  Measuring air conductivity - C(P,T)  Measuring gas purities via conductivity  Possible sensitivity to Lunar activity!  Calibration of a new High Voltage standard

22. John Thornby 4 th April 200722 The End

23. John Thornby 4 th April 200723 Bonus Material…

24. John Thornby 4 th April 200724 Why 63 Ni? Cheaper than Tritium! Well understood Gamow-Teller decay Easy to handle, Ni plating is easy  Can coat ball, box & plate in Ni  Reduce contact potentials Q value 66.945 keV (comparitively high)  We are therefore insensitive to electrons resulting from beta decays of lower Q value sources  Can therefore use Pb shielding!

25. John Thornby 4 th April 200725 Stray Capacitance Require ball’s capacitance to the system Spectrum Reconstruction: Vacuum Chamber (Earth) Source To amplifier… C1C1 C2C2 C3C3 NB: Not to scale To HT system…

26. John Thornby 4 th April 200726 Eliminating Externals 10 -4 mbar vacuum Ball floating (no leakage to ground) Box “boot-strapped” to same potential as ball All surfaces coated in Nickel (no contact p.d)

27. John Thornby 4 th April 200727 Double source control of systematic Pre-spectrometer selects electrons with E>Q-100 eV (10 -7 of the total) Better detectors:  higher energy resolution  time resolution (TOF)  source imaging Main spectrometer  high resolution  ultra-high vacuum (p<10 -11 mbar)  high luminosity Strategy  better energy resolution   E ~ 1 eV  higher statistics  stronger T 2 source – longer measuring times  better systematic control  in particular improve background rejection Goal: to reach sub-eV sensitivity on  M υ  letter of intent - 2001 hep-ex/0109033 KATRIN design report Jan 2005 KATRIN: Next generation MAC spectrometer

28. John Thornby 4 th April 200728 The Kurie plot K(E e ) is a convenient linearization of the beta spectrum Q Q–M c 2 Q K(E) zero neutrino massfinite neutrino masseffect of:  background  energy resolution  excited final states  Q-  E Q (dN/dE) dE  2(  E/Q) 3 And on the Kurie plot…

29. John Thornby 4 th April 200729 Kurie plot  superposition of three different sub - Kurie plots  each sub - Kurie plot corresponds to one of the three different mass eigenvalues The weight of each sub – Kurie plot will be given by |U ej | 2, where | e  =  U ei | Mi  i=1 3 Q – M 3 Q – M 2 Q – M 1 Q E e K(E e ) EeEe Mass Hierarchy

30. John Thornby 4 th April 200730 High Voltage System (work in progress)