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TRImP in-flight separator, ion catcher and RFQ cooler/buncher
E. Traykov TARGISOL Winter School, February 2005 TRImP project and facility In-flight magnetic separator Ion catcher RFQ test and design Simulations Conclusion TRIP Group: G.P. Berg, U. Dammalapati, S. De, P.G. Dendooven, O. Dermois, G.Ebberink, M.N. Harakeh, R. Hoekstra, L. Huisman, K. Jungmann, H. Kiewiet, R. Morgenstern, J. Mulder, G. Onderwater, A. Rogachevskiy, M. Sohani, M. Stokroos, R. Timmermans, E. Traykov, L. Willmann and H.W. Wilschut Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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ISOL vs. In-flight separation
Thick target Diffusion Secondary ion source Electro-magnetic separator Post accelerator needed for secondary reactions Thin target Primary beam and products not stopped in the target Product velocities close to that of primary beam Electro-magnetic separator directly following target Post accelerator not needed for secondary reactions * Drawing taken from Thomas Baumann’s course - Fragment separators Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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TRImP project and facility Beyond the Standard Model
AGOR cyclotron Magnetic separator D Q Q D Production Target Wedge Nuclear Physics MeV Q Q Q D Q Magnetic Separator D Production target Ion Catcher Q keV Q Atomic Physics RFQ Cooler eV meV Ion catcher (thermal ioniser or gas-cell) AGOR cyclotron MOT RFQ cooler/buncher MOT Beyond the Standard Model TeV Physics Particle Physics neV MOT Low energy beam line Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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TRImP separator – a double mode magnetic separator
Fragmentation mode Gas-filled recoil mode * In the gas-filled mode the resolving power is limited by multiple scattering in the gas Target chamber 2 QD QD DD DD QD QD Target chamber 1 Ion catcher + RFQ Low energy beam AGOR HI beam Traps Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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TRImP separator – isotope selection in fragmentation mode
Br = P/q selection Br = P/q selection + Focusing Br 2 Br 3 Br 1 Br 3>Br 2>Br 1 CH2 target 21Na Carbon target 21Na Wanted: 21Na Beam: 21Ne (43 MeV/u) Focal plane dE detector: dE-TOF Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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TRImP separator – isotope selection in fragmentation mode
Br = P/q selection Energy loss + Br = P/q selection + Focusing Degrader selection 21Na Wanted: 21Na Beam: 21Ne (43 MeV/u) Focal plane dE detector: dE-TOF Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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TRImP ion catcher – a thermal ioniser
R. Kirchner, NIM B70 (1992) (* for 208Pb ions, 2300 K, ** ta and t for 238U ions, 2800 K) Thermal calculations using Femlab Diffusion: Delay parameter m0=p2.D/d D=D0.exp(-EA/kT) D: Diffusion coefficient D0, EA: Arrhenius coefficients Effusion: Mean delay time t=1/n=c(ta+tf) ta=C1.exp(C2.DHa/T) ta, tf: sticking and flight times DHa: Enthalpy of adsorption Ionization: Ionization efficiency hi=Na/(1+Na) a=ni/n0=exp((j-Wi*)/kT) N: Amplification factor a: Degree of surface ionization ni,n0: ion and neutral densities Amplification factor < number of collisions (c) Beam from the separator (i.e. 21Na) Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Our RFQ cooler/buncher concept
RF capacitive coupling DC drag resistor chain Electronics designed for large range of isotopes UHV compatible design and materials Standard vacuum parts (NW160) 2 x 330 mm U+VcosWt -(U+VcosWt) Buffer gas pressure (He): Trap position ~10-1 mbar ~10-3 mbar 10eV RFQ ion cooler thermal RFQ ion buncher Switching on end electrodes Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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RFQ cooler prototype tests
RFQ in vacuum Transverse cooling Velocity damping With and without a drag voltage on the segments Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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RFQ cooler/buncher design
Kapton foil 12.5mm 120 pF Stainless steel rods OFHC copper Separate connections for trap segments Preset frequencies: 0.5MHz, 1 MHz, 1.5 MHz Pressure cooler: ~10-1 mbar ~10-3 mbar He buffer gas RF amplitude: 150 V (peak-to-peak) Changeable separation electrodes with different aperture diameters UHV compatible resistors for drag voltage: Uncoated, 2.2 kW Buffer gas: Helium for light ions (i.e. Na-21) (Heavier gas may be considered for Ra ions) Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Simulations and calculation of E field
Real 3D geometry Material properties Geometry separated to smaller parts Fine mesh and grid size 3D electric field map (RF and DC) F(x,y,z,t) = m*(dV(x,y,z,t)/dt) F(x,y,z,t) = E(x,y,z,t)*q dV(x,y,z,t) =(E(x,y,z,t)*q/m)*dt dr(x,y,z,t) =dV(x,y,z,t)*dt FEMLAB calculation examples: RF electric potential DC drag potential Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Ion tracing and distributions
Ion tracing in RFQ guide Buffer gas cooling + DC drag Phase space distributions Ion trapping and extraction Confinement and transmission Program input: Ion charge Ion mass KE Phase space distribution Electric field map (RF and DC) fRF RF amplitude Drag voltage step Gas pressure Standard ion mobility Number of ions Time step Program output: Single ion tracing Confinement Transmission through exit aperture aU qmax = 0.908 qV Mathieu equation: RF only (U=0) Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Optimization using the simulations
Main goal: collect all ions Confinement and transmission Optimize parameters (regions of stable operation): pressure and type of gas aperture diameters beam settings at entrance drag voltage step potentials on separation electrodes accumulation time (buncher) trap potential depth and shape Questions: phase dependence (cooler-buncher) phase dependence (switching) where do we loose ions (why?) Buffer gas pressure RF: 1500 kHz, 21Na+, 10 eV 950 m/s maximum transverse velocity 0.5 V drag voltage step Gas pressure drag voltage ~ 2 eV q=0.5 p=0.025 mbar drag voltage=0.5V Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Drag voltage and pressure dependence
Drag voltage step 21Na+, 10 eV Pressure: 0.01 mbar RF: 1500 kHz 950 m/s maximum transverse velocity f2 mm aperture 0.01 mbar – too low, exit energy high Drag voltage step 21Na+, 10 eV Pressure: mbar RF: 1500 kHz 950 m/s maximum transverse velocity f2 mm aperture 0.025 mbar low pressure limit Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Frequency and focus dependence
21Na+, 10 eV 0.1 mbar buffer gas pressure 950 m/s maximum transverse velocity 0.5 V drag voltage step f2 mm aperture Higher frequency is preferred Maximum transverse velocity 21Na+, 10 eV 1500 kHz radio frequency 950 m/s maximum transverse velocity 0.5 V drag voltage step f2 mm aperture Beam properties at entrance: just focus Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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a q Cool and select RF and DC operation: Mass filter m<M M m>M
Mass selectivity for 23Na+ / 21Na+ m<M M Scan line: U/V = const=0.17 m>M q 0.706 mass resolution frequency Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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LEBL and optimization of parameters (work in progress)
LEBL parts: Extraction tube Einzel lenses Electrostatic steerers Quadrupole deflectors Ion catcher RFQ cooler/buncher MOT ET EL EL Low energy beam line EL EL MOT EL EL EL EL EL QD QD Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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Magneto-Optical Traps for 21Na decay studies (work in progress)
Detector ports Equipotential rings Collector MOT - Designed for optimal collection - Large laser beam diameter Decay MOT - 4p recoil collection - Multi-detector setup for b-detection MCP for recoils Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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TRImP project well on track
Conclusion TRImP project well on track Magnetic separator working, short-lived isotopes separated Work on design and building of a thermal ioniser RFQ cooler and buncher system ready All parts to be tested together soon Trapped Radioactive Isotopes: micro-laboratories for Fundamental Physics
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