Low-pressure hydrogen discharge maintenance in a large-size plasma source with localized high radio-frequency power deposition

Abstract

Articles you may be interested inDevelopment of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments Rev. Sci. Instrum. 83, 083504 (2012); 10.1063/1.4744960 Modeling a high power fusion plasma reactor-type ion source: Applicability of particle methods Phys. Plasmas 19, 043506 (2012); 10.1063/1.3696037 Cesium dynamics in long pulse operation of negative hydrogen ion sources for fusiona) Rev. Sci. Instrum. 83, 02B110 (2012); 10.1063/1.3670347 Simulation of cesium injection and distribution in rf-driven ion sources for negative hydrogen ion generationa) Rev. Sci. Instrum. 81, 02A706 (2010);The development of the two-dimensional fluid-plasma model of a low-pressure hydrogen discharge, presented in the study, is regarding description of the plasma maintenance in a discharge vessel with the configuration of the SPIDER source. The SPIDER source, planned for the neutralbeam-injection plasma-heating system of ITER, is with localized high RF power deposition to its eight drivers (cylindrical-coil inductive discharges) and a large-area second chamber, common for all the drivers. The continuity equations for the charged particles (electrons and the three types of positive ions) and for the neutral species (atoms and molecules), their momentum equations, the energy balance equations for electrons, atoms and molecules and the Poisson equations are involved in the discharge description. In addition to the local processes in the plasma volume, the surface processes of particle reflection and conversion on the walls as well as for a heat exchange with the walls are included in the model. The analysis of the results stresses on the role of the fluxes (particle and energy fluxes) in the formation of the discharge structure. The conclusion is that the discharge behavior is completely obeyed to non-locality. The latter is displayed by: (i) maximum values of plasma parameters (charged particle densities and temperatures of the neutral species) outside the region of the RF power deposition, (ii) shifted maxima of the electron density and temperature, of the plasma potential and of the electron production, (iii) an electron flux, with a vortex structure, strongly exceeding the total ion flux which gives evidence of a discharge regime of nonambipolarity and (iv) a spatial distribution of the densities of the neutral species resulting from their fluxes. [http://dx.

Motivation of concepts for the negative ion extraction from a single element of the matrix source

“…The discharge length L, the dc bias U PE applied to the PE, and its radius R PE have been varied. Figure 2 shows the well-known structure of a planarcoil inductively driven discharge in the ordinary case, for grounded back wall (U PE = 0): high electron temperature T e in the rf power deposition region with maxima of the electron density n e and of the plasma potential Φ there (slightly shifted from each other) 16 and a remote plasma region outside it characterized with a decrease (even a drop) of n e , Φ, and T e till the back wall of the discharge. Figure 3 illustrates the drastic changes in the spatial structure of the discharge when a high bias (200 V) is applied to the PE: (i) the maximum of n e is shifted towards the PE, (ii) the highest value of T e is in the vicinity of the PE, and (iii) smooth axial variation of Φ replaces its axial decrease outside the region of the rf power deposition.…”

Fluid-model analysis on discharge structuring in the RF-driven prototype ion-source for ITER NBI

“…Due to the high degree of dissociation [38], both hydrogen atoms and molecules are accounted for. Although the energy balance of the neutrals and the positive ions is important [31], it is not taken into account, since it does not influence strongly the spatial structure of the charged particle densities [39]. However, the electron energy balance is precisely specified.…”

How to balance computational cost and accuracy of the model for negative hydrogen ion sources? A level-lumping strategy

“…This is because the spatial distributions of the plasma parameters, which are neglected in the global model, also play a significant role in the NHIS. Therefore, a fluid model [15][16][17][18] or a particle-incell/Monte Carlo (PIC/MC) model [19][20][21][22][23][24][25][26] is necessary for us to get deep insight into the plasma characteristics, such as the negative ion production, neutral gas flow, plasma transport and so on. Hagelaar et al developed a two-dimensional selfconsistent fluid model, which included continuity, momentum and energy equations for various species, as well as the Poisson equation and Maxwell equations for describing the electrostatic and electromagnetic fields [15].…”