Development of a novel surface assisted volume negative hydrogen ion source

Abstract

H− ion based neutral beam injector is a critical heating and current drive system in a fusion reactor. However, the present H− ion source configuration has limitations in terms of production, extraction, cesium (Cs) inventory and management. To overcome these limitations, a proof-of-principle experiment based on a novel concept regarding surface assisted volume H− ions production by sprinkling Cs coated tungsten (W) dust grains (low work function surface) into a hydrogen plasma is carried out. Four different diagnostics have been used to validate the concept. The H− ion fraction is estimated from (a) Langmuir probe diagnostic, (b) phase velocity of ion acoustic waves, (c) dust current and confirmed by the measurement of (d) Balmer line ratio. The measured H− ion fraction with respect to the plasma density for different discharge conditions varies from ~0.2 to 0.3 in presence of Cs coated W dust particles. The experimental results show good agreement with the theoretical estimation.

Magnetized plasma sheath in the presence of negative ions

“…14 In low-pressure plasmas, the negative ions are usually created by volume production, 15,16 but the negative ions are also produced by surface production as well. 12 Recently, Kakati et al 17 have developed a novel process of producing negative hydrogen ions (H À ) by cesium coated tungsten dust. They have reported of producing the H À ions by the surface process as it has an advantage over the two-step volume process.…”

“…They have reported of producing the H À ions by the surface process as it has an advantage over the two-step volume process. 17 One of the important parameters for defining negative ion plasmas is electronegativity (a ¼ nÀ ne ). Many researchers have studied electronegative plasmas in the presence of an external magnetic field.…”

Experimental study of charging of dust grains in presence of energetic electrons

“…A comparison of dust currents between the dust samples as shown in figure 11 reveals that Cs coated W dust emits a larger fraction of electrons than that of pure W and Al 2 O 3 dusts. The reason lies in the fact that Cs layer on W lowers the work function [10] (from 4.5eV to 1.8 eV) facilitating in a higher emission rate. Al 2 O 3 dust on the other hand, has a higher SEE yield as compared to W dust, so the electrons are emitted easily from the dust surface which is reflected by a higher dust current in comparison to W. The rate of decrease in the measured dust current with respect to the increase in the discharge current is maximum for Cs coated W, followed by Al 2 O 3 and W. Since, decrease in the dust current consequently refers to electron emission from the dust surface, hence confirms the EEDF findings and validates our assumption about SEE.…”

“…Moreover, cesium coated W dust is also chosen in this study due to its relatively low work function than W and Al 2 O 3 dusts. It also plays a noteworthy role in producing negative ions which are then used for NBI systems in the fusion devices [10,11].…”

Ionization and Single and Double Electron Capture in Proton–Ar Collisions

“…5 The efficient production of H is a critical issue in the design of neutral beam injection systems of fusion devices (Ref. 6 and references therein). Negative ions are also formed in ion or photon interaction with living tissue that takes place in cancer therapy, which has motivated the study of anion-molecule collisions.…”