LIST - Development at Mainz for ISOLDE K. Wendt, T. Gottwald, Ch. Mattolat, C. Ohlert, F. Schwellnus, K. Wies & K. Blaum, Universität Mainz V. Fedoseyev, F. Österdahl, M. Menna, ISOLDE, CERN, Geneva Ch. Geppert, H.J. Kluge, W. Nörtershäuser, GSI, Darmstadt S. Schwarz, MSU, East Lansing, USA
Outline: Motivation for the LIS(&)T Project Experimental Set-up Lasers --- Traps Status of Development and Off-line Test - Measurements in Mainz and at ISOLDE Future Prospects towards the On-line LIST
Motivation for RILIS & LIST Production of isobarically pure ion beams with optimum spatial and temporal ion pulse control using a gas-filled RFQ structure typical ISOL Source Ion Repeller Mass Separator Laser- Beams Ti:Sa 1 Ti:Sa 2 Proton Beam Gas filled RFQ Trap Ion Beam Ti:Sa 3 Nd:YAG HV Platform to Experiments Laser System 1. Atomic Beam Source with Surface Ion Reppeler 2. Gas filled RFQ Trap Section for Bunching and Cooling 3. Mass Separator 4. Laser System
6 kv RISIKO Mass Separator @ UMz ISOLDE 2 Frontend UMz Ti:Sa laser system Orsay Emittance Meter
Mainz Ti:Sapphire Laser Setup Wavemeter ν x 2 ν x 3 Computer- Ti:Sa 3 Ti:Sa 2 Ti:Sa 1 control 1 khz Nd:YAG Pump-laser 532nm, 6 W Pump laser: Tunable lasers: Photonics Industries Nd:YAG, 532 nm, >8 W at 1 khz 2 single & 1 double sided UMz Ti:Sapphire lasers - frequency doubling, tripling and quadrupling - computerized temporal and spectral control
Construction of the LIST RFQ-Trap LIST 1 stabilization rods RFQ segments beam c i n or io c i m ato gas inlet repeller conventional segmented quadrupole structure
Principle of Operation Laser Ionization inside a Gas-Filled Trap Structure Switchable Electrodes Atomizer Atoms Helium Buffer Gas ~ 1-3 mbar Laser Beams Ions Ion Repeller Electron Repeller RFQ Segments UDC 1 mm End Plate Laser Ionization Accumulate Laser Ions Surface Ions Electrons Release SIMION 7.: simulation of the potential distribution Z
Experimental Time Structures 32 potential distribution without buffergas (< 4 1-7 mbar) 315 12 1 Voltageset 1 Voltageset 2 Voltageset 3 31 8 Voltage / V 35 3 29995 Voltageset 1 Voltageset 2 Voltageset 3 Counts 6 4 2 2999 2 4 6 8 1 12 14 3 25 2 z-axis / mm low gas pressure (6 1-5 mbar) Voltageset 1 Voltageset 2 Voltageset 3 6 5 4 6 7 8 9 1 11 12 13 14 ToF / µs high gas pressure (2 1-4 mbar) 3.6 µs Voltageset 1 Voltageset 2 Voltageset 3 Counts 15 Counts 3 6.1 µs 1 2 5 1 27.7 µs 6 7 8 9 1 11 12 13 ToF / µs 6 7 8 9 1 11 12 13 14 ToF / µs
Experimental Time Structures 2 175 15 Tested so far with: Ga, Ca, Ni, Mn laser ions with trap as ion guide pulse structure, trapping 1 pulses without cooling pulse structure with cooling (1ms, 1-3 mbar He) 125 Ions 1 75 FWHM < 7 µs 5 25 25 5 75 1 125 15 175 2 ToF / µs
Time Profile for Different Elements Comparison: time profile 4 Ca versus time profile 58 Ni normalized countrate 1,,8,6,4,2 1.7 µs 2*1-4 mbar 3*1-4 mbar 4*1-4 mbar 5*1-4 mbar Counts 45 4 35 3 25 2 15 1 5 p = 3*1-4 mbar p = 5*1-4 mbar p = 9*1-4 mbar 4.9 µs, 7 75 8 85 9 95 1 ToF / µs 7 75 8 85 9 95 1 ToF / µs Expected longer flight time of nickel ion bunch Significantly broader profile for nickel than for calcium influence of higher atomizer temperature
Maximum Ion Storage Capacity High importance parameter in case of high production rate of neighboring isotopes Integral ion beam,2 na, Trap rate 35 Hz, 5 Lasershots on, 15 off, p = 3.8 1-4 mbar Maximum loading capacity: 4 1 6 Ions / cooling cycle Loss of reasonable ion pulse time profile 12 12 1 1 Counts 8 6 4 ~ 2 µs Counts 8 6 4 ~1 µs 2 2 6 65 7 75 8 85 9 4 5 6 7 8 9 1 11 12 13 14 15 ToF / µs ToF / µs Few ions in LIST trap Maximum loading capability
Efficiency in the LIST Ion Guide Mode 35 3 12 1 Zeitstruktur Ionguide DC auf Masse 25 FC current / pa 2 15 1 4,39 1 12 atoms of 69 Ga collected 6.27 1 12 atoms of 69 and 71 Ga 2 1 17 atoms placed in oven ε = 3.14 1-5 Counts 8 6 4 5 2 5 1 15 2 25 3 35 3 4 5 time / s tof / µs LIST operation as ion guide without buffer gas or trapping, surface ion repeller voltage optimized Distance between source and trap 1 mm 5 mm Efficiency 1,2 1-5 3,2 1-5
Specifications of LIST 1 Measurements on Gallium (IP: 6 ev) LIST RILIS(UMz) Efficiency 2 cm atomizer Suppression of surface ions Trap capacity 5,1 1-5 1,5 1-2 > 1 - > 1 6 / shot - 2 cm oven length Emittance??? - Time structure ~ 5 µs > 5 µs 4 cm oven length Efficiency is fully determined by atomic beam collimation and atomizer length Superposition of RF and DC potentials on the electrodes is cumbersome
Upgrade towards going on-line First Step LIST 2 Separation of RF and DC potentials
Field Shaping in LIST 2 Decoupling of RF and DC: full flexibility of trap and release potential settings Direct and simple access to potentials of each individual DC segment Proper switching of all DC potentials permits pulse shaping 6 1 8 Potentialset 1 Potentialset 2 Trap closed 5 Potentialset 1 Potentialset 2 Potential / V 6 4 Counts 4 3 FWHM 8.2 µs 2 2 width > 6 µs 1-2 2 4 6 8 1 12 14 axiale Position / mm 2 4 6 8 1 12 tof / µs Temporal profile already good without cooling (no buffer gas): FWHM< 8 µs optimum LIST performance also as ion guide with highest efficiency
Optimization of Efficiency with LIST 2 FC Strom / pa 2 15 1 5 1.16 1 14 Atome Ga 69 und 71 insgesamt davon 9,71 1 12 Atome nichtresonant ionisiert ε resonant = 5.35 1-4 Incomplete suppression of background from very high atomic vapor density in trap: - collisional ionization - electron bombardment ionization - field and black body ionization -2 2 4 6 8 1 12 14 16 18 Zeit / s Atomizer length 2 cm 4 cm Efficiency 5,1 1-5 > 5,4 1-4
Emittance Measurements Surface Ions 6 4 2 Ga Oberflächenionen 9.3.7-29, 1, 31, 61, 91, 121, 151, 181, x' /mrad -2-4 211, 24, -6-8 -1 ε rms 1,3 π mm mrad -6-4 -2 2 4 x /mm
Emittance Measurements Laser Ions x'/mrad 6 4 2-2 -4 Ga Laserionen x-richtung 12.3.7-72. 6.667 733.3 146 2187 2913 364 4367 593 582 6547 7273 8-6 -8-1 ε rms ε 1, rms =1.πmmmrad π mm mrad -6-4 -2 2 4 x/mm
First Emittance Measurement @ LIST 2-95. 1 5. 15. 25. 35. 5 45. 55. y' /mrad -5 65. 75. 8. ε rms??? π mm mrad -1-1 -5 5 1 y /mm problem due to diagonal installation of RFQ trap observation of ion motion in trap field solved by 45 rotation
Next step: LIST 3 LIST 3 - simplified cylindrical design - reduced number of electrodes and feed throughs - lower field strength and radial gradients on axis - significantly reduced field induced ion motion - lowest 4 dimensional emittance
Conclusion and Outlook UMz Ti:Sa Laser System off-line (Mz, JYFL, ORNL) and on-line (TRIUMF) in use Investigations on excitation schemes of presently 19 elements, Different LIST prototypes successfully tested at UMz RISIKO Separator Specification measurements on Ga, Ca, Ni and Mn Time structure, loading capacity and (low) emittance determined Measure selectivity and isobare suppression of LIST 3 Determine overall LIST efficiency for different elements Investigate 4d emittance of LIST Diploma thesis TG, june 27 Characterization & set-up of LIST on-line version PhD thesis FS, 27-29