Electronic and Atomic Collisions with Hydrogen and Helium Ions

Transcription

1 Electronic and Atomic Collisions with Hydrogen and Helium Ions State-Specific Study of Associative, Dissociative and Reactive Processes Julien Lecointre, X. Urbain, J. J. Jureta, P. Defrance Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Belgium 1 st Research Coordination Meeting Atomic and Molecular Data for State-Resolved Modelling of Hydrogen and Helium and Their Isotopes in Fusion Plasma IAEA August 2011

2 Outline Three experimental setups ready to use: - Merged-beams experiment - Dissociative charge transfer experiment - Crossed-beams experiment Scientific scope of the project - Ion-Ion collisions - Ion-Atom collisions - Electron-Molecular-Ion Work in progress and to be done

3 Crossed-beams Experimental setup Absolute cross sections for electron impact dissociation and/or ionization The people involved... Université catholique de Louvain, Belgium J. Lecointre, J.J. Jureta, P. Defrance Stevens Institute of Technology, USA K. Becker Universitat Greifswald, Germany H. Deutsch Belgrade University, Serbia D.S. Belic Institut fur Plasmaphysik Julich, Germany R.K. Janev, D. Reiter Leopold Franzens Universitat Innsbruck, Austria T.D. Märk

4 Crossed-beams experiment Selection magnet HeH + Example: HeH + + e - He Ion source (ECR) Collision region Analysis magnet Fragments He + HeH + Lecointre et al, J. Phys. B: At. Mol. Opt. Phys. 39 (2006) 3275

5 Crossed-beams experiment Similar to the CRP on Light Element Atom, Molecule and Radical Behaviour in Divertor and Edge Plasma Regions Period For example: Reaction HeH + +e - Crossed-beams experiment to measure the absolute cross sections for dissociative excitation and dissociative ionization Measurement of the energy thresholds and of kinetic energy release distributions for the considered reactions Deduction of the electronic states contributing in the considered processes Vibrational population depending on the source conditions and the type of sources

6 Merged-beams Experimental setup Total cross sections for the associative ionisation and mutual neutralisation The people involved... Université catholique de Louvain, Belgium J. Lecointre, X. Urbain Columbia University, USA D.W. Savin, K. A. Miller

7 Merged-beams experiment Electrostatic Merging B + Quadrupoles Deflectors Probes Deflectors Deflector B + to electrometer A - neutrals A - AB + ECR Wien filters Beam defining slits Observation cell to electrometer Cylindrical deflectors Zoom on the ion sources Detector Magnetic field Duoplasmatron T. Nzeyimana, E.A. Naji, X. Urbain and A. Le Padellec, Eur. Phys. J. D 19 (2002) 315

8 Study of the Mutual Neutralization reaction H + H + H + H (work in progress )

9 Mutual Neutralization (MN) H + H + H + H Uncertainty of MN cross section M. Stenrup et al, Phys. Rev A 79, (2009) B. Peart and D. A. Hayton, J. Phys. B 25, 5109 (1992) D. Fussen and C. Kubach, J. Phys. B 19, L31 (1986) S. Szücs et al, J. Phys. B 17, 1613 (1984) J. Moseley et al, Phys. Rev. Lett. 24, 435 (1970)

10 MN products detection geometry 225cm MCP biased collision cell MASK 3cm CEM Detection efficiency depends on : -single particle detection efficiency: > 98% for CEM, 57% for MCP - angular spread of both beams (profiles measured in detection plane) -deflection accompanying MN: differential cross section also visible in TOF spectra

11 TOF spectra and angular scattering forward/backward 2000 mev 1500s 1200 mev 1200s 400 mev 900s 120 mev 600s 40 mev 300s 0 mev 120s coincidences 1000 isotropic TOF difference (ns)

12 TOF spectra and angular scattering H + + H - : Coulomb scattering 90 isotropic Deflection angle (deg) Better approximation : - scattering up to avoided crossing with MN channel H+H(n=3) - integration over impact parameter forward/backward Collision energy (ev)

13 Position sensitive detection and KER E r 0 KER = IP[H(n=3)] - EA[H - ] = ev Y (mm) Number of coincidences KER=0.759± X (mm) KER (ev)

14 Absolute cross section for MN of H + and H - Two independent determinations OPTION 1 : measure all relevant quantities - beam currents - form factor (beam overlap) OPTION 2 :measureratio of MN and AI signals H + + H - H 2+ + e - y=8.25e-17 E -1 AI : 15% systematic uncertainty Poulaertet al, J. Phys. B 11, L671 (1978) Cross section (cm -2 ) Collision energy (ev)

15 Absolute cross section for MN of H + and H MN Accumulated signal 100 Ratio = 48 ± 2 10 AI Relative energy (ev)

16 Partial cross section for MN to H + H(n=2, 3) 1000 n=3 Number of coincidences n=2 fast H slow H Inclined Beams TOF difference (ns)

17 Other MN studies : H 2+, He + +H - Peart, Padgettand Hayton, J. Phys. B 30 (1997) 4955

18 Dissociative charge transfer Experimental setup Total cross sections, vibrationalpopulation of molecular ions The people involved... Université catholique de Louvain, Belgium J. Lecointre, X. Urbain Université Libre de Bruxelles, Belgium N. Vaeck, J. Loreau (now at Cfa, Harvard) Université de Bordeaux 1 (CELIA), France B. Pons Universidad Autónoma de Madrid, Spain C. Illescas

19 Study of the HeH + target (work in progress )

20 XUV photodissociationof HeH + Experiments performed at the Free Electron Laser (FEL) FLASH in Hamburg (Germany) HeH + (X 1 Σ + ) + hν (HeH + ) He(1snl 1 L) + H + He + (1s) + H(nl) Experiment H. B. Pedersen et al, Phys. Rev. Lett. 98, (2007) H. B. Pedersen et al, Phys. Rev. A 82, (2010) Theory I. Dimitriuet al, J. Phys. B: At. Mol. Opt. Phys. 42, (2009) K. Sodogaet al, Phys. Rev. A 80, (2009)

21 (a) He + +H(nl) and (b) He(1snl)+H +, for PD of vibrationallyhot (red line) and vibrationally cold (blue line) ions.

22 Present work : Ro-vibrational analysis of the XUV photodissociation of HeH + ions 14 Dissociative charge transfer : 12 HeH +, X 1 Σ + HeH + + K (HeH) + K + He + H + K + 10 C 2 Σ + Potential energy (ev) 8 6 A 2 Σ + B 2 Π 4 2 HeH, X 2 Σ Internuclear distance (a.u.)

23 Ro-vibrational excitation Vibrationalpopulation extracted from measurements performed with a duoplasmatron source operating under conditions similar to FLASH experiment Direct Beam Number of coincidences B 2 Π A 2 Σ DIRECT BEAM 10ms TRAPPING HOT v= 0 55% v= 1 23% v= 2 11% v= 3 7% v= 4 4% T rot 3400 K ms Trapping 20 C 2 Σ Kinetic energy release (ev) COLD v= 0 99% v= 1 1% T rot 3100 K T rot = 3100 K obtained by optical spectroscopy!

24 Total cross section Total cross section for the photodissociation into He(1snl 1 L) + H + starting from the initial state v = 0, J = 0 The cross section for the photodissociation into He + H + weighted by the experimental vibrational distribution BUT : branching towards n>3 states (H* and He* alike) not explained J. Loreau, J. Lecointre, X. Urbainand N. Vaeck, submitted to Phys. Rev. A

25 State-to-state problem to be addressed H + +H 2 (HD, D 2 ) H+H 2+ (v)

26 H + +H 2 (HD, D 2, ) collisions at low impact energies Total cross sections for vibrational excitation and electron capture processes. Theory: P. S. Krstić, Phys. Rev. A 66, (2002). L. F. Erreaet al, Phys Rev A 75, (2007) L.F. Erreaet al, JCP 133, (2010) Experiments: M. W. Gealyand B. Van Zyl, Phys. Rev. A 36, 3091, 1987 T. Kusakabeet al, Phys. Rev. A 70, , 2004 W. H. Cramer, J. Chem. Phys. 35,

27 H + +H 2 (HD, D 2, ) collisions at low impact energies Measurement of the vibrationaldistributions of H 2+ by DCT H 2 target Ion source K target PSD s Partial cross sections for population of individual vibrationalstates of H 2 + and H 2.

28 H. Kreckel, H. Bruhns, K. A. Miller, D. W. Savin Columbia Astrophysics Laboratory, NY Merged Beams Setup for H+H - AD studies H - ion source 10 kv Photodetachment region Partial neutralization of the H - beam inside a drift tube at variable voltages -U f -U f H - + ν IR H + e - Interaction region H 2 molecule formation e - ejected H 2- complex H 2 molecule H - + H H 2 + e - Detection region H 2 stripping in helium H 2 + detection by energy analyzers e - ejected H 2+ ion H 2 + He H 2+ + [He, e - ] 1 m Laser Beam profile monitors Helium gas cell H 2+ detector Bruhns et al, Rev. Sci. Instrum. 81, (2010)

29 H - H photodetachmentscheme Neutralized fraction of the H - beam f PD = C P laser v - H v H- sin (α) 2 m ion beam α laser beam α = 2.7 photodetachment region Top view To reach a photodetachment efficiency of ~10% at 10keV, we need a laser with ~ 2 kw of 1000nm

30 Laser system: interleaved 975 nm 24 mm

31 Measured AD rate coefficient 3.7 mev 1eV systematics Theory: Čížek et al, J. Phys.B 31, 2571 (1998) Langevin rate H. Kreckel, H. Bruhns, M. Čížek, K. Miller, X. Urbain, D. Savin, Science, 329, 69 (2 July 2010)

32 Summary - Three experimental setups ready to use: - Merged-beams experiment - Dissociative charge transfer experiment - Crossed-beams experiment -Study of Ion-Ion, Ion-Molecule and Electron-Molecular-Ion collisions -Fundamental data for collisional processes involving H, H +, H -, He, He +, He 2+, He -, H 2, H 2+, H 3+, HeH +, He 2+ (and isotopes). - Cross-sections for collisions with electrons and collisions among themselves, photon-induced processes, lifetimes of excited states - Comparison and critical evaluation of existing data.

33 Thank you for your attention Universitécatholiquede Louvain UCL Institute of Condensed Matter and Nanosciences IMCN Chemin du Cyclotron 2, B-1348 Louvain-la-Neuve, Belgium Fondsde la RechercheScientifique FNRS Belgium