A new RFQ cooler: concept, simulations and status

1. TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics A new RFQ cooler: concept, simulations and status E. Traykov Krakow, 3-6 June 2004 • TRImP 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

2. TRImP project and facility TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics AGOR cyclotron Magnetic separator D Q Q D Production Target Wedge Q MeV Q Q Nuclear Physics D Q Magnetic Separator D Production target Ion Catcher Q keV Q Atomic Physics eV RFQ Cooler meV Ion catcher (gas-cell or thermal ioniser) AGOR cyclotron MOT RFQ cooler/buncher MOT Beyond the Standard Model TeV Physics Particle Physics neV MOT Low energy beam line

3. RF capacitive coupling 2 x 330 mm • DC drag resistor chain • Standard vacuum parts (NW160) • UHV compatible design and materials • Electronics designed for large range of isotopes TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics Our RFQ cooler/buncher concept 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

4. TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics RFQ cooler prototype tests Tests: • RFQ in vacuum • Transverse cooling • Velocity damping • With and without a drag voltage on the segments

5. Our RFQ cooler/buncher design Stainless steel rods OFHC copper Kapton foil 12.5mm 120 pF ~10-3 mbar He buffer gas Pressure cooler: ~10-1 mbar TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics Separate connections for trap segments Preset frequencies: 0.5MHz, 1 MHz, 1.5 MHz 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)

6. Simulations and calculation of E field TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics • Simulations • 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

7. Ion tracing and distributions TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics • 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 • Phase space distribution • Confinement • Transmission through exit aperture aU qmax = 0.908 qV Mathieu equation: RF only (U=0)

8. Optimization using the simulations Gas pressure  drag voltage Buffer gas pressure RF: 1500 kHz, 21Na+, 10 eV 950 m/s maximum transverse velocity 0.5 V drag voltage step ~ 2 eV q=0.5 p=0.025 mbar drag voltage=0.5V TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics • 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?)

9. 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: 0.025 mbar RF: 1500 kHz 950 m/s maximum transverse velocity f2 mm aperture 0.025 mbar low pressure limit TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics

10. Frequency and focus dependence Frequency 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 TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics

11. Cool and select (work in progress) TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics RF and DC operation: Mass filter a Mass selectivity for 23Na+ / 21Na+ m<M M Scan line: U/V = const=0.17 m>M q 0.706 mass resolution  frequency

12. LEBL and optimization of parameters (work in progress) ET TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics • LEBL simulations: • Extraction tube • Einzel lenses • Electrostatic steerers • Quadrupole deflectors Ion catcher RFQ cooler/buncher MOT EL EL Low energy beam line EL EL MOT EL EL EL EL EL QD QD

13. TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics 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)