A new RFQ cooler: concept, simulations and status Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics E. Traykov TRI P project and facility Our concept Prototype tests Our design Simulations Conclusion TRI P Group: G.P. Berg, U. Dammalapati, 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. Sanchez-Vega, M. Sohani, M. Stokroos, R. Timmermans, E. Traykov, O. Versolato, L. Willmann and H.W. Wilschut Krakow, 3-6 June 2004
TRI P project and facility Ion Catcher RFQ Cooler MOT Beyond the Standard Model TeV Physics Nuclear Physics Atomic Physics Particle Physics Production Target Magnetic Separator MeV meV keV eV neV AGOR cyclotron AGOR cyclotronIon catcher (gas-cell or thermal ioniser) Low energy beam line RFQ cooler/buncher MOT D D D D Q Q Q Q Q Q Q Q Magnetic separator Production target Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics Wedge
Our RFQ cooler/buncher concept Buffer gas pressure (He): ~10 -1 mbar RFQ ion coolerRFQ ion buncher 10eVthermal Trap position U+Vcos t -(U+Vcos t) 2 x 330 mm Switching on end electrodes RF capacitive coupling DC drag resistor chain Electronics designed for large range of isotopes UHV compatible design and materials Standard vacuum parts (NW160) ~10 -3 mbar Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
RFQ cooler prototype tests RFQ in vacuum Transverse cooling Velocity damping With and without a drag voltage on the segments Tests: Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Our RFQ cooler/buncher design Pressure cooler: ~10 -1 mbar ~10 -3 mbar He buffer gas Separate connections for trap segments Changeable separation electrodes with different aperture diameters Buffer gas: Helium for light ions (i.e. Na-21) (Heavier gas may be considered for Ra ions) Kapton foil 12.5 m 120 pF Stainless steel rods OFHC copper Preset frequencies: 0.5MHz, 1 MHz, 1.5 MHz RF amplitude: 150 V (peak-to-peak) UHV compatible resistors for drag voltage : Uncoated, 2.2 k Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Simulations and calculation of E field Simulations Real 3D geometry Material properties Geometry separated to smaller parts Fine mesh and grid size 3D electric field map (RF and DC) RF electric potentialDC drag potential FEMLAB calculation examples: Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics 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
Program input: Ion charge Ion mass KE Phase space distribution Electric field map (RF and DC) f RF RF amplitude Drag voltage step Gas pressure Standard ion mobility Number of ions Time step Program output: Single ion tracing Phase space distribution Confinement Transmission through exit aperture Ion tracing and distributions Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics Mathieu equation: aUaU qVqV q max = RF only (U=0) Ion tracing in RFQ guide Buffer gas cooling + DC drag Phase space distributions Ion trapping and extraction Confinement and transmission
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?) ~ 2 eV q=0.5 p=0.025 mbar drag voltage=0.5V Buffer gas pressure RF: 1500 kHz, 21 Na +, 10 eV 950 m/s maximum transverse velocity 0.5 V drag voltage step Gas pressure drag voltage Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Drag voltage and pressure dependence Drag voltage step 21 Na +, 10 eV Pressure: 0.01 mbar RF: 1500 kHz 950 m/s maximum transverse velocity 2 mm aperture 0.01 mbar – too low, exit energy high Drag voltage step 21 Na +, 10 eV Pressure: mbar RF: 1500 kHz 950 m/s maximum transverse velocity 2 mm aperture mbar low pressure limit Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Frequency and focus dependence Frequency 21 Na +, 10 eV 0.1 mbar buffer gas pressure 950 m/s maximum transverse velocity 0.5 V drag voltage step 2 mm aperture Higher frequency is preferred Maximum transverse velocity 21 Na +, 10 eV 1500 kHz radio frequency 950 m/s maximum transverse velocity 0.5 V drag voltage step 2 mm aperture Beam properties at entrance: just focus Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Cool and select (work in progress) Mass selectivity for 23 Na + / 21 Na + Scan line: U/V = const=0.17 m>M M m<M mass resolution frequency q a RF and DC operation: Mass filter Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
LEBL and optimization of parameters (work in progress) Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics LEBL simulations: Extraction tube Einzel lenses Electrostatic steerers Quadrupole deflectors Low energy beam line RFQ cooler/buncher MOT EL QD ET Ion catcher
Conclusion Novel RF coupling and DC resistor chain tested on prototype RFQ Results from simulations in good agreement with experiment Mechanical, electrical and vacuum design completed RFQ cooler and buncher system ready soon Continue with simulations (LEBL) Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics