Numerical investigation of radio-frequency negative hydrogen ion sources by a three-dimensional fluid model*

Abstract

A three-dimensional fluid model is developed to investigate the radio-frequency inductively coupled H2 plasma in a reactor with a rectangular expansion chamber and a cylindrical driver chamber, for neutral beam injection system in CFETR. In this model, the electron effective collision frequency and the ion mobility at high E-fields are employed, for accurate simulation of discharges at low pressures (0.3 Pa–2 Pa) and high powers (40 kW–100 kW). The results indicate that when the high E-field ion mobility is taken into account, the electron density is about four times higher than the value in the low E-field case. In addition, the influences of the magnetic field, pressure and power on the electron density and electron temperature are demonstrated. It is found that the electron density and electron temperature in the xz-plane along permanent magnet side become much more asymmetric when magnetic field enhances. However, the plasma parameters in the yz-plane without permanent magnet side are symmetric no matter the magnetic field is applied or not. Besides, the maximum of the electron density first increases and then decreases with magnetic field, while the electron temperature at the bottom of the expansion region first decreases and then almost keeps constant. As the pressure increases from 0.3 Pa to 2 Pa, the electron density becomes higher, with the maximum moving upwards to the driver region, and the symmetry of the electron temperature in the xz-plane becomes much better. As power increases, the electron density rises, whereas the spatial distribution is similar. It can be summarized that the magnetic field and gas pressure have great influence on the symmetry of the plasma parameters, while the power only has little effect.

First‐principles Density Functional Theory Elucidation of the Hydrogen Evolution Reaction on TM‐promoted TiC2 (TM=Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au)

“…Within each element period, the atom with the largest atomic number (Zn in the 3 d period, Cd in the 4 d period, and Hg in the 5 d period) exhibited the lowest adsorption strength. This trend is consistent with that observed for TMs adsorbed onto Ti 3 C 2 , γ‐graphyne, MoS 2 , and single‐layer hexagonal boron nitride [50,52–54] . In addition, the adsorption strength of TMs on TiC 2 is greater than that of TMs on γ‐graphyne and weaker than that of TMs on Ti 3 C 2 [50,52] …”

3D fluid model analysis on the generation of negative hydrogen ions for negative ion source of NBI

“…As the pressure increases, the maximum H 2 (w = 2) density becomes higher and moves closer to the left wall of the driver region. A second peak of H 2 (w = 2) density also appears at the right wall at 2 Pa (figure 5(h)) due to the increasing electron temperature there (not shown here) [17].…”

“…Asymmetric electron density, electron energy and potential distributions are formed because electrons are deflected by E × B drift and diamagnetic drift [16,17], resulting in asymmetric collisions and transport (see below).…”

“…In addition, Lishev et al pointed out that the magnetic field penetrating through the driver volume became stronger if the magnetic filter was moved upwards and away from the expansion region, and this resulted in significant plasma asymmetry [15,16]. Wang et al employed a 3D (three-dimensional) fluid model to simulate hydrogen discharges in a reactor with a cylindrical driver region and a rectangular expansion region, and the effects of magnetic filter, pressure, power and magnetic shielding on the plasma properties were studied [17].…”

“…However, due to the computational burden, multi-dimensional simulations of the NHIS are limited. In addition, the chemistry set is usually simplified in the fluid model and the H − ion reactions are usually excluded [17]. Since the generation of H − ions is one of the key issues in an NHIS, it is necessary to establish a multi-dimensional fluid model with H − ions taken into account in a self-consistent manner.…”