Numerical analysis of the production profile of H atoms and subsequent H− ions in large negative ion sources

Abstract

Articles you may be interested inModeling of neutrals in the Linac4 H− ion source plasma: Hydrogen atom production density profile and Hα intensity by collisional radiative modela) Rev. Sci. Instrum. 85, 02B118 (2014); 10.1063/1.4833016 Role of positive ions on the surface production of negative ions in a fusion plasma reactor type negative ion source-Insights from a three dimensional particle-in-cell Monte Carlo collisions model Phys. Plasmas 20, 113511 (2013); 10.1063/1.4834475 Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion sourcea) Rev. Sci. Instrum. 83, 02A719 (2012); 10.1063/1.3673485 Effect of energy relaxation of H 0 atoms at the wall on the production profile of H − ions in large negative ion sourcesa) Rev. Sci. Instrum. 79, 02A503 (2008); 10.1063/1.2802583 Monte Carlo simulation of negative ion production in the negative hydrogen ion source Rev. Sci. Instrum. 71, 883 (2000)The production and transport processes of H 0 atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code is applied to the large JAEA 10 ampere negative ion source under the Cs-seeded condition to obtain a spatial distribution of surface-produced H − ions. In this analysis, the amount of H 0 atoms produced through dissociation processes of H 2 molecules is calculated from the electron temperature and density obtained by Langmuir probe measurements. The high-energy tail of electrons, which greatly affects H 0 atom production, is taken into account by fitting a single-probe characteristic as a two-temperature Maxwellian distribution. In the H 0 atom transport process, the energy relaxation of the H 0 atoms, which affects the surface H − ion production rate, is taken into account. The result indicates that the surface H − ion production is enhanced near the high-electron-temperature region where H 0 atom production is localized.

Progress in modeling and numerical simulation of negative hydrogen ion sources (invited)

“…In addition to the bulk component, the high-energy tail component of electrons, which greatly affects the H 0 atom production, has been also taken into account by fitting a single-probe characteristic as a two-temperature Maxwellian distribution. 8 The result confirms that H 0 atom production is locally enhanced in the high-electron-temperature region as shown in Fig. 3͑a͒, where electrons in the highenergy tail are localized ͑see Figs.…”

“…To understand the origin of the nonuniformity for each production mechanism, a series of numerical modeling of transport processes of primary electrons, neutrals, and H − ions has been done. [5][6][7][8][9] …”

“…To examine the second possibility, a systematic numerical study on the neutral transport has been done. [6][7][8][9] Production and transport processes of H 0 atoms have been numerically simulated using a three dimensional ͑3D͒ Monte Carlo transport code 6 in the realistic 3D geometry of the JAEA 10 A source. The amount of H 0 atoms produced through dissociation processes of H 2 molecules has been calculated from the electron temperature and density obtained by Langmuir probe measurements.…”

Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion source

“…4, FC dissociation (reaction 1 in Table I) has larger reaction rate than others: Dissociations (2)(3)(4) or dissociative ionization (DI) processes (5) which produce H 0 atoms. This is because FC dissociation has a large cross section for low energy region, where the EEDF component has a peak (maximum value σ (E) = 1.2 × 10 −20 m −2 for E = 14 eV) as shown in Fig.…”

Numerical analysis of atomic density distribution in arc driven negative ion sources

“…1 The non-uniformity is mainly decided by spatial distribution of atomic (H 0 ) density, because the negative ions (H − ) are produced on a cesiated low work function surface located around extraction region exposed to fluxes of H 0 atom. 2 The H 0 density distribution is mainly determined from the balance of (1) the production due to H 2 dissociation, (2) the loss due to H 0 ionization, and (3) the transport loss. In previous studies, the H 0 density in H − sources has been investigated by applications of the collisional radiative (CR) model 3,4 and the neutral transport analysis.…”