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

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

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

John Thornby 4 th April 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!

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

John Thornby 4 th April 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-

John Thornby 4 th April 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-

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

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

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

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

John Thornby 4 th April 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

John Thornby 4 th April 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)

John Thornby 4 th April 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)

John Thornby 4 th April 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!

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

John Thornby 4 th April 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

John Thornby 4 th April Electron Collection Demonstration ΔV 0 = V ΔV 1 = V ΔV 2 = V ΔV 3 = 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

John Thornby 4 th April 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

John Thornby 4 th April 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

John Thornby 4 th April 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

John Thornby 4 th April The End

John Thornby 4 th April Bonus Material…

John Thornby 4 th April 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 keV (comparitively high)  We are therefore insensitive to electrons resulting from beta decays of lower Q value sources  Can therefore use Pb shielding!

John Thornby 4 th April 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…

John Thornby 4 th April Eliminating Externals 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)

John Thornby 4 th April 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< 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 hep-ex/ KATRIN design report Jan 2005 KATRIN: Next generation MAC spectrometer

John Thornby 4 th April 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…

John Thornby 4 th April 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

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