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

Abstract

Typical high-energy negative ion electrostatic accelerators such as the ones designed for fusion applications produce a significant amount of secondary particles. These particles may originate from coextracted electrons, which flow from the ion source, impacting the accelerator grids or as by-products of collisions between accelerated negative ions and the residual background gas, in the accelerator. Secondary emission particles may carry a non-negligible power and consequently must be precisely studied. The electrostatic-accelerator-Monte-Carlo-simulation code (EAMCC) [G. Fubiani et al., Phys. Rev. ST Accel. Beams 11, 014202 (2008)] was developed in order to provide a three-dimensional characterization of power and current deposition on all parts of the accelerator. The code includes all the relevant physics associated with secondary emission processes and consequently may be used as a tool for design improvement. In this paper, the two accelerator designs considered for the International Thermonuclear Experimental Reactor, that is, the multiaperture-multigrid and the single gap single aperture (SINGAP) designs, are discussed and their predicted performances compared. Simulations have been compared with measurements on prototype accelerators of the SINGAP type. Reasonable agreement between EAMCC calculations and measurements of backstreaming ions and transmitted electrons was found.

Modeling of plasma transport and negative ion extraction in a magnetized radio-frequency plasma source

“…The vibrational excitation of the hydrogen molecule is maximized at high electron temperatures (typicallyT 10 e eV) while the cross-section for the dissociative attachment of H 2 and hence the production of a negative ion is the largest forT 1 eV vicinity of the PG significantly increases the survival rate of the negative ions and (iii) the magnetic filter more or less lowers the electron flux onto the PG but this is not sufficient and a suppression magnetic field is used to limit the co-extracted electron current. Co-extracted electrons have a damaging effect inside the electrostatic accelerator [4]. The electron beam is unfocused and induces a large parasitic power deposition on the accelerator parts.…”

R&D around a photoneutralizer-based NBI system (Siphore) in view of a DEMO Tokamak steady state fusion reactor

“…Presently, the NBI systems' negative ion beam neutralization is achieved by the stripping of the extra electron from negative ions through collisions with gas injected into the neutralizer cell. It is a simple and reliable method, but the neutralization efficiency is modest (around 55%) and the amount of gas injected both in the source and neutralizer leads to a high background gas density within the accelerating channel such that in the ITER-NBI system, about 30% of the negative ions being accelerated are lost [8] due to molecular collisions, thus contributing to the poor injector efficiency.…”

Physics design of a 100 keV acceleration grid system for the diagnostic neutral beam for international tokamak experimental reactor

“…11͒ which can properly take into account the electric field by the deflected beam. Once these self consistent electric and magnetic fields are imported into a 3D trajectory code such as TRACK or the 3D version of EAMCC, 22 perfect agreement between OPERA-3D and the 3D trajectory code is obtained. …”