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The REX-ISOLDE charge state breeder

The REX-ISOLDE charge state breeder. Fredrik Wenander BE/ABP. ISOLDE Radioactive beam facility Since end of 1967, now 3 rd version 60 keV beams >70 elements and >700 isotopes. REX-ISOLDE Post accelerator to 3 MeV /u Room temperature Linac First experiment 2001.

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The REX-ISOLDE charge state breeder

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  1. The REX-ISOLDE charge state breeder Fredrik Wenander BE/ABP

  2. ISOLDE Radioactive beam facility Since end of 1967, now 3rd version 60 keV beams >70 elements and >700 isotopes REX-ISOLDE Post accelerator to 3 MeV/u Room temperature Linac First experiment 2001

  3. Electrostatic bender Energy slit IHS 7GP 9GP RFQ 5keV/u 300keV/u Magnet Mass slit 2.2MeV/u 3MeV/u 1.2MeV/u 3m A/q separator Linac Type normal conducting 6 accelerating cavities Length 11 m Freq. 101 MHz (202 MHz for the 9GP) Duty cycle 1 ms 100Hz Energy 300 keV/u, 1.2-3 MeV/u (variable) A/q <4.5 * Upgrade to >5 MeV/u in progress * Adding SC cavities after present NC linac

  4. charge bred ions EBIS A/q separator bunched 1+ ions 1+ ions from ISOLDE selected q+ ions to Linac Penningtrap bunching/cooling/breeding mass separator * A/q < 4.5 * beam intensity a few to 109 particles/s * pulsed machine * repetition rate <100 Hz, linac duty factor <10% RF-quadrupole to linac beam from ISOLDE bunched or semi-continuous buncher/cooler

  5. B beam in U trap cylinders REXTRAP principle transversal cooling by side-band excitation of c= q/m B • Radial Cooling • sideband excitation with a quadrupolar field in the transversal plane at the • cyclotron frequency • c = q/m B • coupling of magnetron and reduced cyclotron motion

  6. Trap data • Super conducting solenoid • magnetic field B = 3 T • Length 90 cm • Buffer gas 10-3 mbar Ar, Ne, (He) Preparatory REXTRAP Large Penning trap at REX • * Cooling (10-20 ms) • Buffer gas + RF • * (He), Li,...,U • * Efficiency 45-55 % • * Space charge limit • 108 ions/pulse

  7. Beam out of REXTRAP • From ISOLDE • Semi-continuous (release several 100 ms) • ΔE a few eV • ε ~30  mm mrad (95%) @ 60 keV • Not isobarically nor molecularly clean • After REXTRAP • Bunched beam (t·E ~ 10 s·eV) • Emittance >10  mm mrad @ 30 keV

  8. Axial magnetic field B axial field EBIS cross-view Axial potential Radial potential EBIS basics EBIS Electron Beam Ion Source  High Charge States  Very low Rest Gas Contamination  Variable CSD via Breeding Time  Restricted in Beam Intensity * ~25% in one charge state * More near closed shells Extracted beam has a charge state distribution Charge development

  9. racks collector position insulator electron gun position injection/extraction optics 1+ ions in magnet iron shield q+ ionsout turbo pumps 1 m 60/20 kV platform The REXEBIS REXEBIS • Super conducting solenoid, 2 T • Trap length <0.8 m • Semi-immersed gun (0.2 T) • Warm bore • Breeding time 3 to >300 ms • 50-400 us extracted bunches • Ramped HT potential 20-60 kV • What’s special with REXEBIS? • EBIS + radioactive ions • Few ions 200 to 108 • Warm bore • The high efficiency requirement • Low residual gas ions • General properties • Run with low e-beam neutralisation • Total capacity 6·1010 charges

  10. REXEBIS hardware • Electron beam energy 3-6 keV • Perveance 0.87 A/kV3/2 • 0.5 mm beam diameter (simulated) • Reached Ie=460 mA, normally <250 mA • Normally je=100-125 A/cm2 Manne Siegbahn Laboratory / Chalmers University of Sweden 1.6 mm The REXEBIS The perforated and NEG coated drift tubes The LaB6 <310> cathode

  11. Charge bred beam Extracted beams from REXEBIS as function of A/q showing residual gas peaks and charge bred 129Cs. The blue trace is with and the red trace without 129Cs being injected. Nier-spectrometer – an achromatic separator to select the correct A/q and separate the radioactive ions from the residual gases. q/A resolution ~150

  12. 500 us FWHM Slow extraction, 190Pb44+ measured with Miniball detector N2+ CO+ REX low energy - toolbox for ion manipulation Slow extraction Isobaric mass separation In-trap decay β±-decay Molecular beams Be

  13. Issues / R&D • Reliable electron cathode • -> test alternatives to LaB6 cathodes • 2. Increase electron current to >500 mA • -> modify drift tube structure • 3. Increase electron beam energy to >10 keV • -> modify electron gun • 4. Increased (> 1 ms) or decreased (<30 us) beam extraction time • -> modify drift tube structure Data * LaB6 * Diameter 1.6 mm * Mini Vogel Mount * Crystal orientation <310> * Work function 2.5-2.7 eV * Heating power: without shunt 8-10 W with shunt 6-7 W * Calibration from manufacturer: Temperature vs power calibration No e- emission vs temperature curve * Cathode heating current limited in most cases Manufacturer * AP-TECH * before FEI Beam Technology 1. Reliability and simplicity * new electron cathode type (IrCe, Kimball Physics) 2. Higher electron current/density + heavier elements + faster breeding + larger beam acceptance -> new gun (and collector) design 3. Improved (quantitative) beam diagnostics * tape station after REX mass separator What to improve on EBIS? 1. shortening of the tbreeding 2. continuous injection 3. increased charge capacity >500 mA and >250 A/cm2

  14. Project 1 Setup the TwinEBIStestbench • a. Finalize design and installation of mechanical parts, 6 months • b. Re-commission superconducting solenoid • c. Produce a control system for power supplies, current readouts, • vacuum control system, interlocks. Labview experience, 6-9 months • d. Commission the source, test alternative cathode and gun types, • increase electron beam current and energy. Electron beam • simulations. >12 months • Experienced student(s) • Contact person: F. Wenander New IrCecathode Modified Wehnelt electrode Courtesyof T. Berg TwinEBIStestbench

  15. Project 1b Dedicated investigation of cathode problems Work description The PhD student should make use of the TwinEBIS setup (or REXEBIS during 2013 if possible) in order to understand the 'poisoning effect' of the electron gun cathode and suggest modifications to mitigate the problem. The student should also experimentally evaluate the performance of the IrCe cathode. Furthermore the student should simulate the electron beam and design an electron gun capable of delivering higher (10-15 keV) electron beam energies. If time permits, the student should investigate what is limiting the storage time inside REXTRAP and what can be done in order to improve it.

  16. Project 1c A buffer trap as a debuncher EBIS Breeding to high charge states Mass separation In trap decay Slow extraction Buffer trap CW PseudoCW RFQ cooler 1+ N+ Linear Paul trap Using the energy spread Post acceleration A/q or TOF separation CW injection or bunching in a RF trap Pulsed Goal: to design a debuncher for high intensity bunched beams (from EBIS). Concept: based on linear RFQ widely used either as beam guides and coolers/bunchers. Problem with high intensity bunched beams NUPNET collaboration with e.g. GANIL

  17. Project 3 HIE-EBIS design study Path 1 Path 2 Large capacity, moderate charge state Moderate capacity, very high charge state EBIS test stand Superbreeder for injection into Heidelberg Test Storage at ISOLDE Main design parameters for an upgraded EBIS/T charge breeder aimed to produce VHCI for injection into TSR. Skills needed: EBIS/T design, 5 A electron beams, cryogenic design, 100 kV design, XHV

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