V. I. Mishin Institute for Spectroscopy (ISAN) Russian Academy of Sciences

1. TIME-of-FLIGHT TECHNIQUE for RILIS SELECTIVITY IMPROVEMENT V. I. Mishin Institute for Spectroscopy (ISAN) Russian Academy of Sciences Troitsk, Moscow, 142190 Russia 1st Topical Workshop and Users meeting 2013: Laser Based Particle Sources CERN, Switzerland 20 – 22 February 2013

2. Laser Resonant Ionization Spectroscopy of Radioactive Isotopes in Atomic Beams (1982) Ion Detector ISAN / LNPI experimental setup Laser beams Target and Ionizer Mass separator Neutralizer А+ А+ Atomic beam Protons ISAN & LNPI COMPLIS – ISOLDE MAINZ UNIVERSITY Minimal measurable isotope flow ≈ 103 – 105isotopes/s

3. Laser Resonant Ionization of Atoms in a Hot Metal Pipe (1982) ISAN/Troitsk An excerpt from Mishin’s scientific log book Photoionization Methods for LNPI 1. Ionization in the pipe. laser ions

4. Pi ηRILIS = ≈ 75% Pi+ Pa Laser Resonant Ionization of Atoms in a Hot Cavity. Operating Principle (198 Laser Resonant Ionization of Atoms in a Hot Cavity. Operating Principle (1984) atoms ions + metal plates ISAN/Troitsk HOT CAVITY insulator flaser pulse repetition rate lcavity length υ thermal velocity of isotopes S.V. Andreev, V.I. Mishin,S.K. Sekatsky laser beam Pi /Pa =4fl/υKtr l = 1cm

5. Laser Resonant Ionization of Atoms in a Hot Cavity (1984 – 1988) 1. Rise in the efficiency of ionization of atoms by pulse-periodic lasers S. V. Andreev, V. I. Mishin, S. K. Sekatskiy Sov. J. Quantum Electron., Vol. 15, Num. 3 (1985) 398-400 (English version) KvantovayaElektronika, Volume 12, № 3 (1985) 611-614 (in Russian) Abstract. The possibility is investigated of raising the efficiency of particle interception in the method of resonant photoionization of atoms by laser radiation in a closed hot cavity, located in vacuum, and subsequently employing an electric field to extract the ions formed through a small aperture in the wall. It is shown that for realistic laser radiation parameters (pulse duration ~ 15 nsec, repetition frequency 10 kHz) the cavity geometry can be chosen in such a way that the interception efficiency exceeds 50%. The possibility is demonstrated of completely extracting the ions formed by photoionization from the cavity. • 2. High-efficiency laser resonance photoionization of Sr atom in a hot cavity • S. V. Andreev, V. I. Mishin, and V. S. Letokhov • Optics Communications, Volume 57, Issue 5 (1986) 317-320 • Abstract. The possibility of high-efficiency photoionization of Sr atoms inside a hot cavity with lasers of high pulse repetition rate (104pps) has been studied. The produced photoions were extracted from the cavity through a small hole in its wall for further analysis and counting. An overall photoion yield of about 0.2 has been achieved.

6. Laser Resonant Ionization of Atoms in a Hot Cavity. (1985 – 1988) • 3. Laser resonant photoionization detection of traces of the radioactive isotope 221Fr in a sample • S. V. Andreev, V. S. Letokhov, V. I. Mishin • JETP Letters, Volume 43, Issue 12 (1986) 736-739 (English version) • Pis'maZh. Eksp. Teor. Fiz., Volume 43, Issue 12 ( 1986) 570-572 (in Russian) • Abstract. The hyperfine splitting of the D2 line of the isotope 221Fr (T1/2 = 4.8 min) has been measured. The ionization potential of the francium atom has been refined: Ei ≤ 4.154 eV. • 4. Laser resonance photoionization spectroscopy of Rydberg levels in Fr • S. V. Andreev, V. S. Letokhov, and V. I. Mishin • «Physical Review Letters» • Phys. Rev. Lett., Volume 59, Issue 12 (1987) 1274-1276 • Abstract. We investigated for the first time the high-lying Rydberg levels in the rare radioactive element francium (Fr). The investigations were conducted by the highly sensitive laser resonance atomic photoionization technique with Fr atoms produced at a rate of about 103 atoms/s in a hot cavity. We measured the wave numbers ofthe7p2P3/2→nd2D (n=22–33) and 7p2P3/2→ns2S (n=23, 25–27, 29–31) transitions and found the binding energy of the 7p2P3/2 state to be T=-18 924.8(3) cm-1, which made it possible to establish accurately the ionization potential of Fr.

7. Laser Resonant Ionization of Atoms in a Hot Cavity. (1985 - 1988) • 5. Rydberg levels and ionization potential of francium measured by laser-resonance ionization in a hot cavity • S. V. Andreev, V. I. Mishin, and V. S. Letokhov • «Journal of the Optical Society of America B: Optical Physics» • J. Opt. Soc. Am. B, Volume 5, Issue 10 (1988) 2190- 2198 • Abstract. A highly sensitive method of detecting atoms in samples has been used for spectral investigations of the rare radioactive element Fr. The method is based on laser-resonance photoionization of Fr atoms in a hot quasienclosed cavity. The investigations have been carried out with samples in which short-lived radioactive 221Fr atoms formed at a rate of approximately 103 atoms/sec. The data obtained, to our knowledge for the first time, on the energies of the high-lying Rydberg levels of the 2S½ and 2D series have made it possible to determine the electron binding energy of the 7p 2P3/2 state and to establish the ionization potential of Fr accurately.

8. Laser PhotonizationPulsed Sourceof Radioactive Atoms (1984) (V. S. Letokhov and V. I. Mishin) V.S. Letokhov, V.I. Mishin

9. Laser Ion Sources(1985) H.-Jürgen Kluge, and F. Ames, W. Ruster, K. Wallmeroth Invited talk, givenat the “Accelerated Radioactive BeamsWorkshop” Vancouver Island, Canada4 – 7 September 1985

10. Selective Laser Ion Source (1989) LNPI-ISAN Высокоэффективная z-селективная фотоионизация атомов в горячей металлической полости с последующим электростатическим удержанием ионов Г. Д. Алхазов, В. С. Летохов, В. И. Мишин, В. Н. Пантелеев, В. И. Романов, С. К. Секацкий, В. Н. Федосеев Письма в ЖТФ, том 15, выпуск 10 (1989) 63-66 High efficient z-selective photoionization of atoms in a hot metal cavity followed by electrostatic confinement of the ions G.D. Alkhazov, V.S. Letokhov, V.I. Mishin,V.N. Panteleyev, V.I. Romanov, S.K. Sekatsky, V.N. Fedoseyev Pis'maZh. Tekhn. Fiz., Volume 15, Issue10 (1989) 63-67 Fig. 1. Schematic drawing of the selective laser ion source. The dashed area is the region of ionization.

11. A laser ion-source for on-line isotope separation (1990) ISAN ISOLDE-3 Synchrocyclotron V.I. Mishin, V.N. Fedoseev, Yu.A. Kudryavtsev, V.S. Letokhov, H. Ravn, S. Sundell, H.J. Kluge, F. Scheerer Proceedings of the Fifth International Symposium on “Resonance Ionization Spectroscopy and its Applications, RIS -90”, Varese, Italy (1990) Abstract. A laser ion source has been developed for efficient production of isobarically pure ion beams at the on-line mass separator ISOLDE at CERN. In first off-line tests with radioactive Yb-169, an efficiency of about 15% was achieved. An elemental selectivity between 10 and 104 was observed. The maximum value could be obtained at the off-line separator with TaC as construction material. A first test at the on-line separator ISOLDE-3 was performed recently with Yb isotopes. The lasers produced a pulsed ion beam of about 10 ns pulse length. In order to suppress the continuous background due to surface ionization a pulsed deflector was used so that the selectivity was improved by a factor of 10.

12. Study of Short-Lived 101-108Sn50 Isotopes with RILIS at Heavy Ion Accelerator UNILAC/GSI (1992) laser beams on-line mass separator Ø 1 mm ion beam 106-xSn + 2p + xn extraction electrode E = 1.0 V + + E = 0.01 V + T ≈ 2400 K 40 particle•nA of58Ni14+(5MeV/u) + FEBIAD 50Cr

13. The acronym RILIS was enacted for the first time in 1993 at the ISOLDE/BOOSTER by Slava Mishin, Valentine Fedosseev and Ulrich Köster

14. atoms surface ions photo ions RESONANT LASER IONIZATIONof an ATOM laser beam + + + + + + + A+ sourcecontainer high-temperaturepipe n2 n1 A Operation of a RILIS - - - - - - hotmetal - cavity + - - + + - - + + - - - - - - - - - TRAPPING of IONS by CAVITY PLASMA

15. Selectivity of the RILIS Hot Metal Cavity Two basic factors define RILIS selectivity: *** LASER IONIZATION of studied atoms *** SURFACE IONIZATION of interfering atoms ηLASER (Ag) S(Ag/In) = βSURFACE(In)

16. ISOLDE Overall RILIS efficiencies for elements available at ISOLDE

17. Selectivity of the RILISHot Metal Cavity ηLASER (Ag) S(Ag/In) = βSURFACE (In)

18. TEMPERATURE, oC τ, c Lifetimes of the Sc, Y, Zr, Hf and some lanthanide atoms on the polycrystalline Ta surface J. Beyer, A. F. Novgorodov and V. A. Halkin.JINR preprint Р6 – 9917, 1976 Wall sticking times 1/τ0 – frequency factor Ed – interaction energy of the atom with the surface Frenkel equation The number of collisions of atoms with a wall of the RILISionizer prior to atoms fly out is Swall = πDL N = = 4L/D Shole = πD2/4 L = 3 cm, D =3 mm (length and diameter of the ionizer) N = 40

19. Proton Number Z Neutron Number N

20. S ≈ 10000 It makes sense to hunt for this number Selectivity ofa RILIS can be increased considerably providing laser produced ions are separated from thermal ions T laser pulse-repetitioninterval τions creation time= τlaser pulse duration time Maximum RILIS selectivity, which can be reached by laser ions separationfrom thermal ions, is equal toS = T / τions flaser = 104 pps T = 1/flaser = 100 μs τions = τlaser≈ 10 ns

21. ISOLDE ISOLDE RILIS ≈ 140 mm ≈ 140 mm ≈ 140 mm ≈ 140 mm 30 mm 30 mm 30 mm 30 mm IONIZER IONIZER Ions to mass separatormagnets IONIZER IONIZER Laser beams in ionizer Laser beams in ionizer Laser beams in ionizer Laser beams in ionizer TARGET TARGET TARGET TARGET ≈ + 2 V Repelling electrode ≈ + 2 V Repelling electrode ≈ + 2 V Repelling electrode ≈ + 2 V Repelling electrode - 60 kV Acceleration electrode - 60 kV Acceleration electrode - 60 kV Acceleration electrode - 60 kV Acceleration electrode Ground plate Ground plate Ground plate Ground plate

22. + + + + + + + + + + + + + + + + + + 0 V - 64V + + + + + + + + + COMPARISON of an ISOL Time-of-Flight RILIS and the Time-of-Flight Mass Spectrometer There is a significantdiscrepancybetween the TOF mass spectrometer and ISOL TOF RILIS1. Initial ion spatial distributions TOF MS ≈ 0.3 mm TOF RILIS 30 mm 2. Voltage applied to the TOF electrodesTOF MS ≈ 5000 V TOF RILIS ≥ 50 V 3. linear dimensionTOF MS 40 - 200 cm TOF RILIS ≈ 12 cm The Wiley-McLaren TOF massspectrometer SourceDrift region Extraction Acceleration region region 0.2 cm 1.2 cm 40cm - 1600 V - 1600 V Ground Extraction Acceleration Detector plate grid grid An ISOL TOF RILIS Source – Hot cavityDrift regionAcceleration region + 3 cm 3 cm 80 cm 30 V - 60 000 V Repelling electrode Ground grid Ground grid Acceleration electrode

23. Ion packets width τion peaks ≈ τspatial distributions+ τthermal energy distributions

24. Broadening of ion packetsby initial spatial distributions acceleration region field free drift-region τspatial distributions E=0 +V

25. τturn-around time = t1 – t0 Broadening of ion packetsby initial thermal energy distributions acceleration region field free drift-region τturn-around time E=0 +V t1 t0 t0 t1 L υ0- initial thermal velocity m- mass of ions e - charge of electron

26. Uacceleration - 60 kV Uionizer 30 mm ionizer target Duration of ion packets at the outputof the mass separator in relation to the voltage drop across the RILIS ionizer M = 100 a. e. J. Lettry et al. (2002) Δτ(Ag) ≈ 50 – 60 μs τspatial distributions+ τturn-around time The voltagerangeaffect the mass separator resolution M. Koizumi et al. (2002) Δτ(Al) ≈ 10 μs

27. Melting Points and Resistivity of the Refractory Metals and Carbon Niobium Molybdenum Tantalum Tungsten Rhenium Meltingpoint 2750 K 2896 K 3290 K 3695 K 3459 K Resistivity Tungsten 5.6×10−8Ω•mat 20 °C Carbon (crystalline) 2.5×10−6to 5.0×10−6 Ω•m// basal plane 3.0×10−3 Ω•m⊥ basal plane Carbon remains solid at higher temperaturesthan the highest melting point metals such as tungsten or rhenium. Carbon sublimation point about 3900 K.

28. The temperature of the crystalline graphite pipe in relation to the voltage drop The electrical resistance ofthe pipe about2.7 Ω

29. τion peak ≈ τturn-around time Primary Space Focus for Single-Stage Source Region Configuration Source – Hot cavityDrift regionAcceleration region E = E0E = 0 E = E1≈60 000 kV/L + + + + + + + + + s D = 2s Acceleration Ground Ground plate grid grid

30. L = 37 mm Ø3 mm s D = 2s 3,7 cm 3,7 cm Experimental Setup Carbon (amorphous) atomic vapoursource

31. Time-of-flight mass spectrum of Li+, Na+, K+ and Tm+ current generator triggering pulse Uionizer = 15.3 V 5 ms photodiode response on the laser pulse Tm (thermal) and Tm (laser) peaks are created through Tm ionization on the hot cavity surface or by the laser laser ablation of the grid

32. E = E0E = 0 M = 100 a. e. Acceleration Ground Ground plate grid grid + + + + + + + + + D = 2s s = + Broadening of ion peaksby initial spatial distributions Broadening of ion peaksby initial thermal energy distributions Primary Space Focus for Single-StageSource Region Configuration Duration of ion peaks, μs Voltage applied to the ionizer, Volts

33. Summary • • • The hot cavity made of crystallinegraphite can operate stable at high temperatures (≥2000oC) • • • The voltage applied to the cavity may be as much as 30 V • • • Short ion pulses approaching 3 μs can be prepared by the use of the crystallinegraphite hot cavity • • • The RILIS selectivity can be increased by a factor of 30 – 50 for isotopes of mass 100 with the crystalline graphite hot cavity and single-stage TOF configuration