ALCBEAM – Neutral beam formation and propagation code for beam-based plasma diagnostics

ALCBEAM is a new three-dimensional neutral beam formation and propagation code. It was developed to support the beam-based diagnostics installed on the Alcator C-Mod tokamak. The purpose of the code is to provide reliable estimates of the local beam equilibrium parameters: such as beam energy fractions, density profiles and excitation populations. The code effectively unifies the ion beam formation, extraction and neutralization processes with beam attenuation and excitation in plasma and neutral gas and beam stopping by the beam apertures. This paper describes the physical processes interpreted and utilized by the code, along with exploited computational methods. The description is concluded by an example simulation of beam penetration into plasma of Alcator C-Mod. The code is successfully being used in Alcator C-Mod tokamak and expected to be valuable in the support of beam-based diagnostics in most other tokamak environments.Program summaryProgram title: ALCBEAMCatalogue identifier: AEKU_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKU_v1_0.htmlProgram obtainable from: CPC Program Library, Queenʼs University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 66 459No. of bytes in distributed program, including test data, etc.: 7 841 051Distribution format: tar.gzProgramming language: IDLComputer: Workstation, PCOperating system: LinuxRAM: 1 GBClassification: 19.2Nature of problem: Neutral beams are commonly used to heat and/or diagnose high-temperature magnetically-confined laboratory plasmas. An accurate neutral beam characterization is required for beam-based measurements of plasma properties. Beam parameters such as density distribution, energy composition, and atomic excited populations of the beam atoms need to be known.Solution method: A neutral beam is initially formed as an ion beam which is extracted from the ion source by high voltage applied to the extraction and accelerating grids. The current distribution of a single beamlet emitted from a single pore of IOS depends on the shape of the plasma boundary in the emission region. Total beam extracted by IOS is calculated at every point of 3D mesh as sum of all contributions from each grid pore. The code effectively unifies the ion beam formation, extraction and neutralization processes with neutral beam attenuation and excitation in plasma and neutral gas and beam stopping by the beam apertures.Running time: 10 min for a standard run.

► We present a new 3D neutral beam formation and propagation code ALCBEAM.
► It was developed to support the beam-based diagnostics on magnetic fusion devices.
► The code provides beam energy fractions, density profiles and excitation populations.
► It takes into account 3D effects of beam formation, not typically included in other NBI codes.
► The processes of beam attenuation by plasma, neutral gas and scrapers are also included.