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Cooling of Highly-Charged Ions in a Penning Trap

Cooling of Highly-Charged Ions in a Penning Trap. SMILEtrap ( S tockholm- M ainz I on LE vitation trap ) Team: T. Fritjoff, Nagy Szilard (PhD student ) , R. Schuch, Atomic Physics Department, Stockholm University

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Cooling of Highly-Charged Ions in a Penning Trap

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  1. Cooling of Highly-Charged Ions in a Penning Trap SMILEtrap (Stockholm-Mainz Ion LEvitation trap)Team: T. Fritjoff, Nagy Szilard (PhD student), R. Schuch, Atomic Physics Department, Stockholm University I. Bergström,Manne Siegbahn Laboratory, Stockholm U. K. Blaum, GSI/CERN • Penning trap (SMILE) connected to an electron-beam ion source (EBIS) with isotope injector for mass measurements • Exploit highly charged ions for mass measurements, because c=q/mB • An accuracy in 10-10 range for atomic masses is reached by ion selection without cooling. • Do we really need (want) cooling? How far down can one get? • Prospects of evaporative cooling and adiabatic cooling • Electron cooling

  2. Ion Budget • Precision Trap • After injection aperture : 150 ions • Captured : 50 ions • After energy selection : 1-4 ions (2V- 50 mV) PreTrap • After magnet and retardation : 106 ions • 1/250 beam captured : 4000 • pretrap length/beam length • 2 V deep trap / 7 eV energy spread • EBIS • delivers: e.g. 108 Geq+ ions • 25% on Ge22+ : 2.5x107 ions

  3. Mass Measurements using SMILETRAP • Full computerized control (LabVIEW) • Easy, comfortable to handle

  4. High Resolution Mass Spectrometry with Heavy High-q Ions • Result from 208Pb and 198Hg runs:

  5. Projects in SMILEtrap collaboration with relevance for HITRAP • Goal: • reach mass uncertainty of < 0.1 ppb for very highly charged heavy ions • 0.1 ppb is in reach for light ions • Behind this success were the following measures: • 1. Stabilisation of the trap temperature • 2. Stabilisation of the helium pressure • 3. Stabilisation of the frequency synthesizer • 4. The use of short measurement cycles (2 min) • 5. The use of H2+ as a intermediary mass reference • 6. The fast exchange (a few s) between the mass of ref. ion and the ion of interest. • 7. The application of Ramsey excitation • 8. Exactly calculated binding energies (Lindroth and Indelicato) • And now a table which summarizes our results:

  6. Isotope q+ Atomic mass (u)Uncertainty(ppb) 1H 1 1.00727646666(90)0.90 3H 1 3.016 049 278 4(29)0.96 3He 2 3.016 029 323 5(28)0.93 4He 2 4.002 603 256 8(13)0.33 20Ne 9, 10 19.992 440 186(14)0.70 22Ne 9, 10 21.991 385 115(19)0.86 28Si 12, 13, 14 27.976 926 531 (14) 0.50 36Ar 13, 14 35.967 545 105(15)0.42 76Ge 22, 23 75.921 402 758(96)1.3 76Se 24, 25 75.919 213 795(81)1.1 86Kr 26 85.910 610 729(110) 1.3 133Cs 36, 37 132.905 45159(41)3.1 198Hg 52 197.966 768 4(6)3.0 204Hg 52 203.973 494 2(6)2.9

  7. Systematic Errors • Q/A dependence : • Origin : misalignment of the trap and B : • use mass doublets to minimize this effect  q/A ( B ) Proton mass deduced from C,N, Ne,Ar - or ion cooling!?

  8. How could we check? • Examples : Agreement between charge states for SMILEtrap values!

  9. Cooling forces the ions to the same position i. e. in the trap center. We can accept occupying a larger radial region because of perfect large Mainz trap and sampling many ions in the destructive time-of-flight. This kind of ion control can also be achieved by increasing trapping field gradient • Is cooling absolutely necessary? • Yes, for the resonant circuit pick-up detection(Seattle, MIT, Harvard groups) they use ion and ref. ion and need them in the same position. We still have to show for mass measurements how far we can go by selection rather than cooling. Essential also for HITRAP, but other experiments may need cooling (g-factor, cold ions,…)

  10. Evaporative cooling t 2.3 kV -5V V ions from EBIS 2.3 kVq t -1 kV pre-trap precision trap

  11. Adiabatic cooling is based on invariant of action integral with adiabatic change of fields in this case: 1/B dB/dt << c angular momentum L=rmvi is invariant therefore vi has to decrease when r increases as B decreases t Example (Li et al. Z.Phys.D22, 375,91) for dense U92+ cloud z=1cm, B = 3 T  0.08 Tesla T = 300K  10 K density 106  4.7 103 cm-3

  12. Electron (positron) cooling cooling times: tcool = k /q2 memi ve2/ne Lc tcool = 8.9 s (kTe)3/2 A/neq2 [kT(eV), ne (107cm-3)] warm ions cold e- Electron-ion recombination (radiative for bare ions) RR = 5 1013 Z2/(kTe)1/2 cm3/s Ratio: tcool/tRR = 3 10-3 A kTe(eV) Resistive cooling times tcool = k mi /q2 R

  13. Present Plans in SMILEtrap • testing limits in accuracy with present set-up: • 204-208Pbq+, Thq+, Caq+ ,He+,2+, 3H+ masses • Development of Ramsey method • for standard procedure in data taking and analysis • Q-value measurements • Input for neutrino mass determination • Installation of new 1.2 T pre-trap magnet: • Test of evaporative cooling • Test of e- cooling

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