Penetration of energetic neutral beams into fusion plasmas

Abstract

The efficiency of neutral beam heating and current drive depends crucially on the deposition of the energy and momentum of the beam in the plasma. This deposition is determined by the atomic processes involved in the stopping (or effective ionization) of the neutral beam atoms. These processes have been studied in detail for the energy range from 10 keV/u to 10 MeV/u. The processes considered include both the ground state and the excited state of the beam atoms, thus allowing for the multistep ionization of the beam in collisions with the plasma constituents and impurities. The effective beam stopping cross-section has been calculated for a wide variety of beam and plasma parameters. The atomic database necessary for these calculations has been documented using the best data available at present. The stopping cross-section data are also given in terms of a convenient analytic fit, which can be used either in computer calculations or for simpler analytic estimates of neutral beam penetration.

The beam emission spectroscopy diagnostic on the DIII-D tokamak

“…Fluctuations in the observed signal are directly proportional to the local density fluctuations through a proportionality constant that depends on local electron temperature and density: dn/nϭK(T e ,n e )dI/I. 6,7 The neutral beam viewing optical system consists of a custom-designed f /2, f ϭ40 cm, objective lens, 25 cm vacuum window, in-vessel shutter, optical axis-folding mirrors ͑to avoid a toroidal field coil͒ and scannable 2D motorized fiber-mounting array, all shown in Fig. 1.…”

Calculation of ionization and total and partial charge exchange cross sections for collisions of C6+ and N7+ with H

“…The aim of this work is firstly to study the differences of charge exchange cross sections at low energies in [21] and secondly, to recommend accurate ionization cross sections for collisions with H(n = 1, 2), which are of interest for the beam penetration into the plasma [37,38]. The calculations have been carried out by employing a CTMC method with improved initial distributions.…”

Simulation of the neutron rate in ASDEX Upgrade H-mode discharges

“…Its convolution with the fusion cross-sections from [19] and a maxwellian distribution yields the beam-plasma fusion rate, whereas a self-convolution returns the beam-beam reaction rate. For the beam ionisation the Janev model [20][21] is used. A dedicated study has shown that using different beam stopping cross sections has a negligible effect on the NBI deposition profile for ASDEX Upgrade H-mode discharges [21].…”