Gas jet laser ionization: developments towards selective RIB production and studies of exotic atoms Iain Moore JYFL, Finland I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Outline of talk General introduction to RIB production Probing the gas jet In-jet laser ionization Outlook I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
General methods of RIB production (I) ISOL method High-energy Born in 1951, Niels Bohr Institute primary beam Radioactive atoms kV Low-energy ion beam High yield but difficult for refractory elements, chemically active elements. Mass selection Z and T 1/2 dependence ISOL facilities: TRIUMF, GANIL, ALTO, ISOLDE (Wed. talks) SPES (Thurs.) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
General methods of RIB production (II) In-flight method High-energy First in-flight separator, Oak Ridge (1958) primary beam Projectile fragments Isotope selection Medium-energy ion beam Very fast separation, access to μ s half-lives and beams of ALL elements. Often poor beam quality. Precision experiments at low-energy not directly accessible. I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
The ion guide / gas catcher method …an ISOL system for ALL elements, fast extraction Projectile source ``The best of both worlds´´ Fast beams Purification in-flight Thin target Neutralization Ion survival electrical fields mass separator Laser re-ionization Z selectivity; IGISOL Laser Ion Guide I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Principles of laser ionization non-resonant excitation of ionization of ionization auto-ionizing states Rydberg-states ionization extraction potential field or ~6 eV (5-9 eV) collisional s I ~ 10 -17 cm 2 s I ~ 10 -15 cm 2 ionization higher excited states energy first E 1 excited state s R ~ 10 -12 cm 2 ground state E 0 0 eV Z Efficiency × Selectivity N I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
JYFL: a high-repetition rate laser system repetition rate: ~ 10 kHz • • tuning range: - fundamental 700 - 1000 nm - frequency doubled 350 - 500 nm - frequency tripled 240 – 330 nm - frequency quad. 205 - 250 nm • laser linewidth: > 5 GHz (broad) Talk by Volker, 11:20 <1 GHz (narrow) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
IGISOL-4: 2012 - from K=130 MeV cyclotron https://www.jyu.fi/fysiikka/en/research/accelerator/igisol Off-line ion sources: (discharge, carbon cluster …) K=30 MeV Laser transport cyclotron for optical manipulation Laser ionization in-source/in-jet Collinear laser spectroscopy Decay spectroscopy Mass spectrometry & post-trap spectroscopy IGISOL – second floor I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
In-gas-cell laser ion source Ar/He Laser beams from gas Longitudinal purifier Separation of stopping and laser ionization volume improves: • Laser ionization efficiency at high cyclotron beam current Beam from Cyclotron • Increasing selectivity (collection of non-neutral ions) Target Laser Ionization Ionization chamber chamber Ion Ion Collector Filament collector Talk by Yuri, Exit hole Thurs. 15:50 Ø 0.5 – 1 mm SPIG Yu. Kudryavtsev et al., NIM B 267 (2009) 2908 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
General introduction to RIB production Probing the gas jet In-jet laser ionization Outlook I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Why do we wish to use the gas jet? …a quest for PURE radioactive ion beams → (the Laser Ion Source ``Trap´´) I.D. Moore et al., AIP Conf. Proc. 831 (2006) 511 Hot cavity LIST (talk by S. Richter, Fri. 10:40) F. Schwellnus et al., Rev. Sci. Instrum. 81 (2010) 02A515 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Improvements in resolution The effect of temperature and pressure on the FWHM Hot cavity (ISOLDE) Doppler broadening (2000 - 2500 K) Pressure broadening Gas cell (LISOL/JYFL) (300 K) Laser resolution 1.8 GHz T. Sonoda et al., NIMB 267 (2009) 2918 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
What challenges do we face? • Time overlap between fast atoms and laser pulses Velocity distribution laser ion guide (JYFL) Reference cell T. Kessler, PhD thesis (JYFL) Gas cell He 200 mbar Velocity distribution of jet (CFD simulations) 1500 m/s 7 GHz blue shift Gas jet = 1660 m/s jet 0 m/s T. Sonoda et al., NIMB 267 (2009) 2918 Courtesy of J. Kurpeta (Warsaw) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Solution: a high-repetition rate laser system SPIG V dc = +40 V 59 Cu (T 1/2 =81.5 s) On-line reaction: 58 Ni( 3 He-25 MeV,np) 59 Cu In-jet production ~ 60× < in-gas cell production R. Ferrer-García, V. Sonnenschein et al., NIM B 291 (2012) 29 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Second challenge: laser-atom spatial overlap Properties of the gas jet depends on nozzle shape and pressure boundaries Planar laser-induced fluorescence Numerical investigation of jet flows NASA Technical Reports Server, Record 59, M. Jugroot et al., J. Phys. D 37 (2004) 1289 J.A. Inman et al., (2008) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Imaging gas jets at JYFL • Create a gas discharge • Photograph the expanding jet • Vary background pressure 32 mm • Vary nozzle type • Model rf sextupole • Analyse the jets ~700 V converging-diverging exit hole perspex SPIG de Laval nozzle I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
From image to analysis Variations in background pressure 0.146 mbar 5 10 0.226 mbar 0.329 mbar 0.588 mbar 1.180 mbar Intensity (arbitrary units) 2.339 mbar 4 10 4.352 mbar 5.640 mbar 3 10 2 10 -60 -40 -20 0 20 40 60 Radial position (mm) 100 1.45 mm exit hole, 25 mbar 1.45 mm exit hole, 56 mbar 1.45 mm con-div, 56 mbar Jet FWHM (mm) ~ 1 mbar is suitable for jet 0.6 mm exit hole, 56 mbar • acceptance into rf device φ spig = 6 mm 10 • Not suitable conditions due to discharge 1 0 1 2 3 4 5 6 7 Background pressure (mbar) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Probing the jet from a de Laval nozzle Images and direct pressure measurements P Ar = 250 mbar 240 Flow Direction 200 Stagnation pressure (mbar) P Ar = 300 mbar 160 𝛿 𝛿−1 1 𝛿−1 𝛿 + 1 𝑁 2 𝑞 𝑗 𝛿 + 1 120 = 𝛿 − 1 𝑁 2 + 2 2𝛿𝑁 2 − 𝛿 + 1 𝑞 𝑗𝑜 80 −1 40 𝑊 2 = 𝛿 − 1 𝑁 2 1 + 𝛿 − 1 𝑁 2 2 ∙ 𝑊 𝑛𝑏𝑦 0 2 2 60 50 40 30 20 10 0 -10 -20 Distance from the nozzle exit (mm) With the Mach number we can also determine: • jet temperature • jet density M. Reponen, I.D. Moore, I. Pohjalainen et al., NIMA 635 (2011) 24 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
General introduction to RIB production Probing the gas jet In-jet laser ionization Outlook I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Laser spectroscopy of Ni: gas cell vs. gas jet 1.2 Reference cell 0.8 Normalized count rate (a.u.) 0.4 0.0 1.2 Gas cell He 50 mbar 0.8 0.4 0.0 1.2 ~ 5 GHz Gas jet 0.8 0.4 0.0 231.164 231.166 231.168 231.170 231.172 Wavelength (nm) 5 GHz blue Doppler shift; ~ 1130 m/s jet velocity • • Laser linewidth dominant ( ~ 9 GHz at 232 nm) M. Reponen, I.D. Moore et al., EPJ A 48 (2012) 45 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
A stepwise improvement in laser linewidth • Addition of a second etalon into the Ti:sapphire cavity Thick etalon Thin etalon undoped YAG coated substrate Birefringent d = 6 mm d = 0.3mm filter R = 8% R ≈ 40% Ref. cell FWHM = 6.6 GHz FWHM = 2.0 GHz (Talk by T. Kron, Thurs. 17:10) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Spectroscopy of 63 Cu (LISOL 2011) Reference cell COG FWHM = 2.9(2)GHz Ion signal (a.u.) Gas cell P Ar = 150 mbar FWHM = 4.3(2)GHz Gas jet FWHM = 3.2(2)GHz CoG = 2.5(2)GHz n – 1227.45887 (THz) V jet ~600 m/s R. Ferrer, V. Sonnenschein et al., NIMB 291 (2012) 29 I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
First free jet ions in LIST geometry at JYFL ( 65 Cu, Nov. 2012) 40000 1st step 30000 -1 ] Count rate [s 20000 I sat = 17 mW/cm 2 10000 0 0 100 200 300 400 500 600 700 1.0 -2 ] Laser intensity [mW cm 65 Cu (LIST) 0.8 60000 4.3 GHz FWHM 2nd step 50000 0.6 40000 -1 ] Arbitrary Count rate [s I sat = 119 mW/cm 2 30000 0.4 20000 0.2 10000 0 0 5000 10000 15000 20000 0.0 -2 ] Laser intensity [mW cm -20000 -10000 0 10000 20000 3rd step, I sat ~ 3.2 W/cm 2 Frequency (MHz) I.D. Moore, 1st Topical Workshop on Laser-Based Particle Sources, Feb. 2013
Recommend
More recommend
