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Development of a Novel Charge Spectrometer at IoP Nuclear and Particle Physics Divisional Conference

This presentation discusses the development of a new charge spectrometer, including its motivation, how it works, empirical principles, experimental details, and recent results. It also reviews the applications, goals, and outlook of the spectrometer.

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Development of a Novel Charge Spectrometer at IoP Nuclear and Particle Physics Divisional Conference

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

  2. Overview • Motivation for a new technique • How it works • Empirical principles • Experimental details • Instrument characterisation • Recent results • Review: Applications, Goals and Outlook

  3. Acknowledgements & Disclaimer Acknowledgements: Dr. Yorck Ramachers, Adrian Lovejoy, Disclaimer: This is not strictly a Nuclear Physics talk!

  4. 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. The Idea… • Past experiments basically count electrons • Replace with a continuous rate of change observable?

  6. The Idea Continued C • β-isotope used as a current source • Charges a capacitor (simply a charge collector) • Charges converted to Voltages • Obtain an integrated β-spectrum e- Isource VC

  7. e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- So, how does it work? • Process self-quenches: • Accrued e- provide increasing retardingpotential → Cost and noise-free!  • Only most energetic e- overcome repulsion • Eventually no more electrons will make it… • Corresponds to end-point energy. Measure it! Source Collector 63Ni

  8. Integrated β-Spectrum Only rare high-energy electrons contribute → dVC/dt small End-point @ dVC/dt = 0 Most electrons energies contribute → dVC/dt large

  9. Now the clever part… • Capacitor actually a dipole magnetball bearing… • Magnetically levitated & held ~ 10-4 mbar vacuum • Accrued charge cannot escape!

  10. Levitating the Ball • Magnetic forces balance gravity • Unique in-house designed electronics • Provides stable, reproducible configuration Levitation coil Permanent Magnets Hall Probe

  11. Levitation Electronics • Ball equilibrium maintained with μW Power!

  12. 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. 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. Contact potential Calibration Vball(V) ~ 0.2 × VPSD(mV) • Induced AC voltage on pickup proportional to DC voltage on ball • PSD Returns an error voltage

  15. 2mV band Collector Insulation • 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. Charging the Ball in vacuum • Can we charge the ball in vacuum? • β/conversion electron isotopes • Stimulated emission electrons

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

  18. 0 V ΔV0 = 0.903 V -250 V increments, every 5 minutes ΔV0 = ΔV1 + ΔV2 + ΔV3 -1.5 kV ΔV1 = 0.030 V -1.75 kV ΔV2 = 0.315 V -2.0 kV ΔV3 = 0.561 V Electron Collection Demonstration Offset consistent with genuinely charging the ball

  19. Ball Voltage vs. Time 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)

  20. Outlook, Review and “to do” list… • Exciting and innovativeprototype experiment • Demonstrated insulation & charging of collector • Next step is to use a real source in vacuum • Calibrate HT controller • 109Cd, mono-energetic particles as a reference • Measure Capacitance of ball to surroundings (non-trivial) → Air/Vacuum conductivity • Perform tests in a variety of configurations

  21. Potential Applications • β-endpoint →υ mass • Possible sensitivity to neutrino mass hierarchy • Air & vacuum conductivity - C(P,T) • Gas purities via conductivity • Calibration of a new High Voltage standard • Possible sensitivity to Lunar activity! SUGGESTIONS WELCOME!

  22. The End

  23. Bonus Material…

  24. Why 63Ni? • 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. Source C3 C1 To HT system… C2 To amplifier… NB: Not to scale Vacuum Chamber (Earth) Stray Capacitance • Require ball’s capacitance to the system • Spectrum Reconstruction:

  26. 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. letter of intent - 2001 hep-ex/0109033 Goal: to reach sub-eV sensitivity on Mυ • Strategy • better energy resolution  DE ~ 1 eV • higher statistics  stronger T2 source – longer measuring times • better systematic control  in particular improve background rejection KATRIN design report Jan 2005 Pre-spectrometer selects electrons with E>Q-100 eV (10-7 of the total) • Better detectors: • higher energy resolution • time resolution (TOF) • source imaging Double source control of systematic • Main spectrometer • high resolution • ultra-high vacuum (p<10-11 mbar) • high luminosity KATRIN: Next generation MAC spectrometer

  28. zero neutrino mass finite neutrino mass • effect of: • background • energy resolution • excited final states Q  (dN/dE) dE  2(dE/Q)3 Q-dE And on the Kurie plot… The Kurie plot K(Ee) is a convenient linearization of the beta spectrum Q K(E) Q–Mnc2 Q

  29. The weight of each sub – Kurie plot will be given by |Uej|2, where 3 |ne = SUei |nMi  i=1 K(Ee) Q – M3 Q – M2 Q – M1 K(Ee) Q Ee Ee Mass Hierarchy • Kurie plot  superposition of three different sub - Kurie plots • each sub - Kurie plot corresponds to one of the three different mass eigenvalues

  30. High Voltage System (work in progress)

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