G Ban 1 M Breitenfeldt 2 P Finlay 2 X F abian 1 X Fléchard 1 P Friedag 3 F Glück 5 A Knecht 6 V Kozlov 5 E Liénard 1 G Soti ID: 787537
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Slide1
WITCH, a Penning Trap for Weak Interaction Studies
G. Ban1, M. Breitenfeldt2, P. Finlay2, X. Fabian1 X. Fléchard1, P. Friedag3, F. Glück5, A Knecht6,V. Kozlov5, E. Liénard1, G. Soti2, M. Tandecki2, S. Van Gorp2 , Ch. Weinheimer3, D. Zákoucký4, N. Severijns21LPC-Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, Caen, France2Instituut voor Kern- en Stralingsfysica, KUL, Leuven, Belgium3Universität Münster, Institut für Kernphysik, Münster, Germany4NPI Rež, Czech Republic5Karlsruhe Institute of Technology, Institut fur Kernphysik, Germany6CERN, Geneva, Switzerland
T. Porobić2,
Slide2Outline
Introduction & motivationOverview of the WITCH experimentRecent results & analysisInvestigation of the systematic effects - SimWITCH3D - Space-charge effects - Detector efficiencyOutlook
Slide3Motivation: New Physics
Beta decay:Search for physics beyond the standard modelHigh energyDirect production - LHCHigh precisionLow energy – β-decay Observables: Energy, angular correlations Historical: Parity violation on Co Our focus: beta-decay of 35Ar
Slide4Motivation
Fermi transitionvectorscalarννe-e-recoil
recoil
Why measure the recoil spectra of
35
Ar
?
Standard Model: Vector, Axial-Vector
Non-SM: Scalar, Tensor
Standard Model
Non-SM
H
β
= H
Vector
+
H
Axial
+
H
Scalar
+
H
Tensor
Standard Model
Non-SM
Slide5The
WITCH experimentCooled and bunched beam of 35Ar @ 30 keVPulsed drift tube for decelerationBuffer-gas cooling of the ions in 1st Penning Trap (Cooler Trap)Decay of the ions in the 2nd Penning Trap (Decay Trap) Probing the ions’ recoil energy in the SpectrometerCounting the ions on the main MCP
Slide6Penning traps at WITCH
Scattering-free sourceHe buffer gas in the cooler trapDipole excitation at magnetron ω- frequency – mass independent removal from trap centerQuadrupole excitation at cyclotron frequency ω
c – mass selective centering & buffer gas --> cooling of the ion cloud
Slide7WITCH:
Spectrometer9 T magnet High field (9 T) at the traps, low (0.1 T) in the analyzing plane Adiabatic approximation: field gradient in a single cyclotron gyration radius is small Ecycl /B is an adiabatic invariant -> if Bsource >> Bplane , then Ecycl,plane
<<Ecycl,
source Combination of electrostatic filter and inhomogenous mag. field => high energy resolution + high statistics
Slide8November 2012 online experiment
Further improvements of the diagnostics, measurement systems and transmission New data acquisition system from LPC Caen More information in the datastream High background level High ret.potential
Low ret. potential
High ret.potential
High
ret. potential
Low
ret. potential
High
ret.potential
Retardation potential (V)
Number of ions (arb.)
Experimental cycle
Retardation spectrum
Retardation spectrum extracted
Systematic effects still not fully accounted for
Studies of main MCP energy-dependent efficiency ongoing
Preliminary, uncorrected
Slide9Systematic effects investigation
1. Spectrometer effects - 2D symmetry breaking structures found, upgrading tracking simulation software to 3D was needed2. Penning trap effects - investigation of space-charge effects with offline ions and simulations 3. Main MCP energy dependent efficiency - 1+, 2+, 3+ charge states of decay products - reacceleration in front of the main MCP results in different energies for charge states
Slide101. SimWITCH: Ion tracking simulation
in the spectrometerMonte Carlo ion tracking in the spectrometerOriginally 2D, recently upgraded to 3DTracks the recoil ions from the trap to the Main MCPIon transport simulated for various retardation voltages (0 V – 450 V)Also for all 35Ar charge states (1+, 2+, 3+, 4+, 5+) (charge state measurement by LPC trap@GANIL [1])Axial symmetry broken by a diagnostic MCP and anti-ionization wire[1] Electron shakeoff following the
β+
decay of trapped
35
Ar+
ions
, Couratin et al, submitted
Slide11Diagnostic MCP
Diagnostic MCP and anti-ionization wire affected ion trajectories significantly Repositioned the MCPWire
Diagnostic MCP
Wire
After MCP repositioning
Before MCP repositioning
Slide12SimWITCH-3D:
influence of the wire on the potential in the spectrometer Wire – map of potential difference Wire influence on the potentialX-Z planeThe potential in the center is higher by ~1.1 V (0.5%)Implemented by Paveł Bączyk, ISOLDE summer studentUpgraded SimWITCH to include 2D symmetry breaking elementsWire – map of potential difference Wire influence on the potentialX-Y plane
Slide13The potential in the
center is higherby ~38 V (1.3%)SimWITCH-3D: diagnostic MCP influence on the potential in the spectrometerWire – map of potential difference MCP influence on the potentialX-Z planeWire – map of potential difference MCP influence on the potentialX-Y plane
Slide14Deflection of the ions can be simulated!
Influence on the ions – preliminary simulation resultsWithout the MCP With the MCP
Slide152. Simbuca
: ion cloud dynamics and space-charge1S. Van Gorp et al. Nucl. Instr. and Meth. A 638 (2011) 192-200.Ion cloud in the traps simulations: Simbuca1Simbuca: calculates ion cloud evolution in ion traps for large numbers of ions using GPU parallelization
Simulated many-ion space-charge effects: cyclotron & magnetron resonant
frequency shift, energy and other systematic effects
Of interest to wider ion trapping
community
To be published
Slide16Simbuca: Transfer between traps
Transfer time - very sensitive to electric field imperfections, provides information on trap systematicsColler trap – decay trap transfer scan Decay trap energy scan
Slide17Simulation agrees well with experimentMinor differences caused by transient states of the power supply
Simulation [2]Simbuca: Transfer between traps [2] E. Wursten, Master Thesis
Slide183. Main MCP detector
8 cm diameter delay lines, position resolution 0.2 mmTotal efficiency is 40(11)%Found energy dependent efficiency for 0 – 6 keV ions – major systematic effect Caused by wear of the plates
Slide19MCP test bench at LPC-Caen
Study of MCP energy effiency with a Na+ ion sourceEnergy of can be varied 0 – 6.5 keVAbsolute efficiency measuredMesh connected to an electrometer
Slide20MCP energy dependent efficiency
Our MCP efficiency increases with ion energyMore data needed (with 39K+ ions, improved improved normalization) for a precision correction of online data
Slide21Summary & outlook
Retardation spectrum extractedSimWITCH-3D code successfully models systematics of the ion tracking, including axial symmetry breakingSimbuca code successfully simulates ion cloud evolution in the traps and transfer between traps, including space-charge effectsMCP efficiency crucial for extracting the β-ν correlation coefficient, further study needed