H. Tawara

P. Fainstein

R.D. Rivarola

T.W. Imai

National Institute for Fusion Science (NIFS-Repository)

§ 1. The Partial Cross Sections of Neutral Hydrogen Atoms Formed in Electron Detachment from Negative Hydrogen Ions in Collisions with Positive Ions at High Energies Imai, T.W. (GUAS), Tawara, H. Rivarola, R.D. (Instituto Fisica de Rosario, Argentina) Fainstein, P. (Centro Atomico Bariloche, Argentina) N eu tral hydrogen atom beams are used in the plasma heating. In order to obtain the high en-· ergy (rv 11e V) and powerful (rv 11W) neutral hy-drogen atom beam for NBI, H- ions have to be converted into neutral hydrogen atoms, HO, with better efficiencies. \Ve have calculated the partial cross sections for the electron detachment from negative hydro-gen ions colliding with protons, H+ + H- --* H+ + HO(ls and 2s) + e-. (1) In the present work, we consider not only the ground state H°(1s) but also the excited state HO(2s) in the exit channel. In order to calculate the electron detach-ment cross sections, we used the Four-Body Continuum-Distorted-Wave (4B-CDW) approx-imation [1 rv 4]. There are two electrons with different binding energies in H- ions in the ground state: one is the tightly bound Is electron (ionization energy ~ 13.6 eV) and the other is the loosely bound Is' electron (ionization energy ~ 0.75 eV) in the Hylleraas-Eckart function [5], and these energies are reflected on the detached electron wave func-tion in the exit channel [6]. Figure 1 shows the calculated partial cross sections for the reaction (1). The solid line de-: notes those for production of the ground state neutral hydrogen atoms, H°(1s), and the dot-ted line those of the excited state neutral hy-drogen atoms, HO(2s), in the exit channel. The calculated results show that the cross sections of production of HO (Is) is far larger than those of HO(2s). The excited state HO atoms are easily ionized before reaching the main plasmas, thus reducing the conversion efficiencies in applications to NBI. Thus, the present results suggest that collisions with positive ions are much better than those for neutral atoms [5] because fractions of the excited state HO (2s) atoms are very small. H+ + H- --> H+ + HO(ls and 2s) + e-1 0- 13 ro---'---'--"-'-'-'n-rr--.,---,.--r--.-.-r-rr---.---.-..-.-.-.-r-T":I § 10-16 ',p u (I) V) Vl 10-17 Vl o '-u 10-18 ........... -_ ............... -.................. . ........ ...... ............ .......................... -- H- -> H(ls) + e . ..•........ H- -> H(2s) + e-1 0- 1 9 L----'----'--'-'-'-............,._~-'--'---'-'-..L..I..I.-_ ............. __'__'-'-'-...... 101 102 103 Incident Energy (keV) Fig. 1. Calculated partial cross sections for elec-tron detachment of the reaction (1). The solid and the dotted lines represent those for hydro-gen atoms in the ground state, HO (Is), and those with hydrogen atoms in the excited state, HO(2s), respecti vely. References [1] Dz. Belkic, Nucl. Instrum. 1\1ethod. B 124, 365(1997) [2] Dz. Belkic, J. Phys. B 30, 1731 (1997) [3] Dz. Belkic, 1. Mancev and V. Mergel, Phys. Rev. A 55, 378 (1997) [4] R. Gayet, J. Hanssen, L. Jacqui, A. Martinez and R. Rivarola, Phys. Scri. 53, 549 (1996) [5] T. W. Imai, H. Tawara, R. D. Rivarola and P. Fainstein, J. Phys. B 32, 1247 (1999) [6] H. Shull and P. -0. LOwdin, J. Chern. Phys. 25, 1035 (1956) 315 

The Partial Cross Sections of Neutral Hydrogen Atoms Formed in Electron Detachment from Negative Hydrogen Ions in Collisions with Positive Ions at High Energies

The Partial Cross Sections of Neutral Hydrogen Atoms Formed in Electron Detachment from Negative Hydrogen Ions in Collisions with Positive Ions at High Energies

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)