Charge Exchange Spectroscopy

Quantitative charge exchange spectroscopy is a key diagnostic tool at most fusion laboratories and will be at ITER, where a diagnostic neutral beam is planned. The scope of such analysis continues to expand with a move to heavier elements, especially argon, in progress. Such heavier elements, which may be partially ionized over core regions of the fusion plasma, link active charge exchange emission shell localization and transport. ADAS-EU will enable and support such developments. The work packages of this theme will support hydrogen, helium and lithium beam diagnostic models/ analysis and will extend the fundamental databases for the new species and new energy ranges. The provision and support will include both spectral fitting and spectral analysis packages. Specially commissioned studies will again secure the precision of the atomic data and atomic models.

Workpackage WP6: Shared CXS analysis

Charge exchange spectroscopy is a central diagnostic for fusion laboratories in Europe and a key diagnostic for ITER. A shared objective is a common analysis framework and codes which will freely allow cross-studies and become established as the standard for ITER. The framework will have a machine independent core with interfacing access procedures for specific machines/spectroscopy/beams/data archiving. There are two shared developments (FZJ, IPP, & JET principals) (1) CXSFIT a spectral fitting code, designed for composite CXS spectral interval with sophisticated graphical user interface and capabilities - virtually complete; (2) NEW-CHEAP a CXS spectral line interpretative analysis for plasma parameter, impurity concentrations with sophisticated forward and reverse modelling, predictive capability and error propagation - in development. ADAS staff lead the practical development and maintain the system but it is independent of the ADAS Project. The objective is to enable and interface these codes and analysis methods for all European fusion laboratories and ultimately ITER. Embedding of these capabilities in the experimental programmes at Euratom Associated Laboratories. Such embedding is a central objective of the ADAS-EU proposals and the preparations for ITER. Certain orbit and geometric orientation effects will be calculated and embedded as universal corrections in NEW-CHEAP.

Workpackage WP7: Universal heavy element CXS modelling

Charge exchange spectroscopy is in the process of extension to heavier species (argon and beyond) with issues of the role of CX for highly ionised ions of heavy elements such as tungsten. Upper emitting levels of visible CXS lines advance to higher n-shell at high z where collisional mixing establishes a bundle-n population model. State selective CX cross-section data for highly ionised ions must be based on extrapolated universal parametric forms established at low/moderate z. Several adjacent ions of a heavy element are simultaneous receivers at a localised point each emitting many transitions. The appropriate models are enabled here delivering the complete sets of CXS emissivity coefficients for use in analysis with heavy elements.

Workpackage WP8: Transport and multiple charge state CXS

For elements of nuclear charge >~18, the charge exchange receivers may not be the bare nucleus over significant regions of the plasma. Simultaneous multi-chord CXS observations of lines from adjacent stages are localised along the beam line and the inferred radial distributions reflect impurity transport directly. Support of this scenario requires a CXS receiver population modelling adjusted for a non-empty ion core and predictive modelling of local emission along a beam pencil with receiver ionisation stage fractional abundances from a transport model. A novel cross-validation experiment type targeting transport parameters and consistency of passive emission along lines of sight may be possible by alternating between active and passive observations while stepping up through heavier species. The present tasks will enable these types of analysis. Embedding of these capabilities in the experimental programmes at Euratom Associated Laboratories. Such embedding is a central objective of the ADAS-EU proposals and the preparations for ITER.

Workpackage WP9: CXS data and fiducial embedding

Objectives The fundamental state-selective charge exchange cross-section database for sub-dominant levels depends on the CTMC model for energies >~50 keV/amu. relevant to ITER . Extension of the database to receiver charge states >10 needs the improved CTMC approximation. Calculations, currently extending to z=18, are required to substantially higher charge states and n-shells to satisfy the fusion application need and to revise the present universal parametric forms. Higher precision calculations at lower energy <~ 50keV for Ar+16 - Ar+18 in CCMO and CCAO approximation will support the next phase of CXS diagnostic development.