Modeling of secondary emission processes in the negative ion based electrostatic accelerator of the International Thermonuclear Experimental Reactor

Abstract

The negative ion electrostatic accelerator for the neutral beam injector of the International Thermonuclear Experimental Reactor (ITER) is designed to deliver a negative deuterium current of 40 A at 1 MeV. Inside the accelerator there are several types of interactions that may create secondary particles. The dominating process originates from the single and double stripping of the accelerated negative ion by collision with the residual molecular deuterium gas (' 29% losses). The resulting secondary particles (positive ions, neutrals, and electrons) are accelerated and deflected by the electric and magnetic fields inside the accelerator and may induce more secondaries after a likely impact with the accelerator grids. This chain of reactions is responsible for a non-negligible heat load on the grids and must be understood in detail. In this paper, we will provide a comprehensive summary of the physics involved in the process of secondary emission in a typical ITER-like negative ion electrostatic accelerator together with a precise description of the numerical method and approximations involved. As an example, the multiaperture-multigrid accelerator concept will be discussed.

Design of the “half-size” ITER neutral beam source for the test facility ELISE

“…An intensive cooling is foreseen to remove the heat load from the plasma and back streaming positive ions. This heat load has been downscaled from the ITER value of 880 kW [7] to 26.4 kW for the ELISE size and acceleration voltage (60kV). The cooling channels are milled into the stainless steel back plate and closed by a 1 mm thick electro deposited copper layer, also along the cone.…”

Analysis of the two accelerator concepts foreseen for the neutral beam injector of the International Thermonuclear Experimental Reactor

“…One of the main drawbacks of the negative ion electrostatic accelerators for high power NB injectors is the significant amount of secondary particles which are produced inside the accelerator [4]. Secondary particles originate from collisions between the accelerated negative ions and the residual background gas and from the collisions between particles (primary or secondary) and material surfaces in the accelerator.…”

“…While the ITER-MAMuG accelerator has been simulated in a previous work [4], the SINGAP concept still needed to be theoretically investigated. The paper is organized as follows: Sec.…”

“…The paper is organized as follows: Sec. II gives an overview of the physics involved in secondary particle production and reviews the features of the electrostatic-accelerator-Monte-Carlosimulation code [4] (EAMCC). EAMCC was specifically developed to model secondary emission processes inside high-energy electrostatic accelerators.…”

Photodetachment cross-section evaluation using asymptotic considerations

“…As a first option, negative ion beam neutralization could be realized by injecting a gas into the neutralizer cell, but under a low efficiency level around 55% (corresponding to an electric efficiency of the heating system limited to 34%) [13]. Another possible option is the photoneutralization process [12,14,15] that can be seen as an attractive alternative [16], as no gas is injected into the medium to neutralize the negative ions (less parasitic particles produced, no plasma formation in the cell).…”