Recombination reactions and commissioning of DESIREE sa Larson

Recombination reactions and commissioning of DESIREE Åsa Larson & Mats Larsson

Outline • Recombination reactions • The H 2 system Åsa • The He. H system • The Be. H system • Commissioning of DESIREE Mats

Recombination reactions

Recombination reactions … … relevant for the fusion plasma of the divertor. • Light atomic/molecular ions H, He, Be, …, O • Relative low energies (E<20 e. V) • Different isotopes • Different vibrational states v=0, 1, 2, … • Total cross section, final state distributions and differential cross section • H- might be present

Recombination reactions … Electron-molecular ion collisions A+B+ Direct/indirect Dissociative recombination (DR) AB+ AB** A++BA* +B AB*

Recombination reactions … Electron-molecular ion collisions Resonant A+B+ ion-pair formation (RIP) AB+ AB** A++BA* +B AB*

Recombination reactions … Electron-molecular ion collisions Vibrational A+B+ excitation/deexcitation (V AB+ AB** A++BA* +B AB* Direct/resonant

Recombination reactions … Electron-molecular ion collisions Dissociative excitation (DE) A+B+ AB** A++BA* +B AB* Direct/resonant

Recombination reactions … Anion-cation collisions + Mutual (MN) A+Bneutralization AB+ AB** A++BA* +B AB*

Recombination reactions … Anion-cation collisions + Double transfer (DCT) A+Bcharge AB+ AB** A++BA* +B AB*

Recombination reactions … Anion-cation collisions A+B+ ionization (AI) Associative AB+ AB** A++BA* +B AB*

Recombination reactions … Anion-cation collisions Electron A+B+ detachment (ED) AB+ AB** A++BA* +B AB*

The H 2 system

H++H- collisions

The H 2 system H 2 adiabatic potential energy curves 1Σ + g symmetry

H+ + H- Mutual neutralization H+ + H- →H(n) + H • Calculate the cross section for the mutual neutralization reaction at low collision energies (< 100 e. V). • Fully quantum mechanical – electronic – vibrational – rotational • Accurate structure calculations FCI (11 s, 8 p 7 d, 2 f) → [9 s, 8 p, 7 d, 2 f] • Include all states up the H(n=3)+H and H+ + H • Strict diabatization • Identical nuclei • Log-derivative method M. Stenrup, Å. Larson and N. Elander, Phys. Rev. A 79, 012713 (2009).

H+ + H - Mutual neutralization Total neutralization cross section M. Stenrup, Å. Larson and N. Elander, Phys. Rev. A 79, 012713 (2009).

H+ + H - Mutual neutralization Branching ratios M. Stenrup, Å. Larson and N. Elander, Phys. Rev. A 79, 012713 (2009).

H+ + H - Double charge transfer H+ + H- →H- + H+ Good agreement with other theoretical studies but a factor of 10 larger than measured ones. J. Zs. Mezei, M. Stenrup, N. Elander and Å. Larson, Phys. Rev. A 82, 014701 (2010).

H+ + H - Mutual neutralization Differential cross section A quantum study is needed! w e n ! h t ain i w rb ed. U r pa y X m sb o c nt e b me l il ri W pe ex

H+ + H - Mutual neutralization Differential cross section Isotope dependence

H+ + H Why quantum? Mutual neutralization Semi-classical Landau-Zener study H+H(n=3) H+H(n=2) Us tes e H + ts ys + H tem a ! sa H- +H+ Very sensitive to crossing points and coupling strengths! Try different methods to obtain couplings

H+ + H - Mutual neutralization Compare with QM cross section and branching ratios

H+ + H - Mutual neutralization Semi-empirical method: “Olson 1” Effective ionization potential of electron which is transferred from reactants (electron negativity) R. E. Olson, J. R. Peterson and J. Moseley, J. Chem Phys. 53 3391 (1970).

H+ + H - Mutual neutralization Semi-empirical method: “Olson 2” Effective ionization energy of the electron in the product state R. E. Olson, F. T. Smith and E. Bauer, Appl. Opt. 10 1848 (1971).

H+ + H - Mutual neutralization Semi-empirical method: “Olson 3” R. E. Olson, J. Chem Phys. 56 2979 (1972).

H+ + H - Mutual neutralization Using the “Landau-Herring method” B. M. Smirnov, Sov. Phys. Dokl. 10 218 (1965); 12 242 (1967). “Smirnov”

H+ + H - Mutual neutralization Using the “Landau-Herring method” R. K. Janev, Adv. At. Mol. Phys. 12 1 (1976). “Janev”

H+ + H - Mutual neutralization Ab initio 2 x 2 transformation: Conclusion: Janev and ATD work best!

The He. H system

The He. H system Combining structure and electron scattering calculations Adiabatic resonant states of He. H (FCI) Very highly excited states!

Resonant DE He. H+ + e- →He. H* →He + H+ + e- (Results from previous CRP meeting) C. Strömholm et al. , PRA 54 3086 (1996).

Direct DE He. H+ + e- →(He. H+)* + e- →He+ + H + e- Feshbach resonances!? Remove the resonance contribution from the T-matrix Develop a t-dep method C. Strömholm et al. , PRA 54 3086 (1996).

The He. H system Non-adiabatic couplings are presently calculated Strict diabatic transformation Quantum study of high-energy DR, RIP and MN. Inclusion of autoionization.

The Be. H system

DR of Be. H+ Direct DR (Previous CRP meeting) Indirect mechanism + VE:

Mutual neutralization? Be+ + H- →Be. H*→Be* + H Avoided crossings with 9 states of 2Σ+ symmetry Ab initio calculations are hard! Semi-classical LZ method with the Janev couplings. J. Pitarch-Ruiz et al. , J Chem Phys. 129 054310 (2008)

Mutual neutralization? Be+ + H- →Be. H*→Be* + H Large cross section Small isotope effect

Mutual neutralization? Be+ + H- →Be. H*→Be* + H Many states contribute

● R. D. Thomas, H. T. Schmidt, G. Andler, M. Björkhage, M. Blom, L. Brännholm, E. Bäckström, H. Commissioning of DESIREE Danared, M. Gatchell, N. Haag, P. Halldén, Dag Hanstorp F. Hellberg, H. A. B. Johansson, A. Källberg, G. Källersjö, M. Larsson, S. Leontein, L. Liljeby, P. Löfgren, B. Malm, S. Mannervik, A. Paál, P. Reinhed, K. G. Rensfelt, S. Rosén, K. Schmidt, A. Simonsson, M. Stockett, J. Weimer, H. Zettergren, and H. Cederquist ● Department of Physic, Stockholm University

Detector for neutral reaction products Quadrupole doublet 10° Deflection Drift tube merging section From platform 1 Outer vessel Thermal screen Inner vessel From platform 2 160° Bend Port for laser light Variable deflections

Next step ● Inject and store ions at room temperature in the asymmetric ring ● Cool down the ring again to 15 K ● Start merged beam experiments: H+ + H