CRP F43023 on Data for Atomic Processes of Neutral Beams in Fusion Plasma (2016-2020) (Short title: Neutral Beams)

Summary

Neutral beam injection is a standard method to heat the plasma in fusion experiments and it is intended to be used for power control in ITER and perhaps in a reactor. Neutral beams also have important diagnostic uses, both via photoemission from the beam neutrals due to interaction with the plasma and via photoemission from plasma impurities after interaction with the beam. Modelling of beam penetration into the plasma and of the spectroscopic signals relies on detailed data for atomic processes that involve the neutral beam particles. In spite of the importance of the data there are quite significant gaps, especially related to processes starting from an excited state of the neutral atom. On the other hand, for processes starting from the ground state of the neutral atom there are often several different families of calculated or measured data, obtained using different approximations or experimental methods, and it is important to assess their uncertainties and to recommend best data.

The Coordinated Research Project (CRP) on Data for Atomic Processes of Neutral Beams in Fusion Plasma is intended to provide evaluated and recommended data for the principal atomic processes relevant to heating and diagnostic neutral beams in fusion plasmas. The primary emphasis is on processes of hydrogen (H, D, T) neutral beams in the high temperature core plasma.

Preliminary Consultancy Meeting

IAEA Consultants Meeting on Data Evaluation for Heavy Particle Collision Processes, IAEA Headquarters, Vienna, Austria, 17-18 March 2016.

Research Coordination Meetings

First Research Coordination Meeting: IAEA Headquarters, Vienna, Austria June 19-21, 2017

Meeting report and presentations

Second Research Coordination Meeting: Foreseen for about Q3, 2018.

Third Research Coordination Meeting: Foreseen for Q4 2019 or Q1 2020.

Incidental Related Meetings

Code Comparison Workshop on Electron Dynamics in Atomic Collisions. Under consideration as a one-week event organized with cooperation from IAEA sometime early in 2017.

Code Comparison Workshop on Neutral Beam Penetration, Beam Emissions and Beam-based Diagnostics. Under consideration.

Research Groups Participating in the CRP

O. Marchuk, FZJ, Germany, Atomic data and collisional-radiative modelling of neutral beams in eigenstates.

J. Ko, NFRI, Korea, Experimental validation of atomic data for motional Stark effect diagnostics.

D. Stotler, PPPL, USA, Neutral Beam Analysis Codes Used on NSTX-U and DIII-D.

G. Pokol, Wigner Research Centre, Hungary, Study of atomic beam interactions in fusion plasmas using the RENATE synthetic BES diagnostic.

M. O'Mullane, U of Strathclyde, UK, Quantification of the contribution of processes in the ADAS beam model.

A. Dubois, UPMC, France, Electronic processes cross sections evaluation with semiclassical non perturbative approach.

T. Kirchner, York University, Canada, Basis Generator Method Calculations for Ion-Atom Collision Systems of Relevance to Neutral Beams in Fusion Plasma.

A. Kadyrov, Curtin University, Australia, Accurate calculations of state-resolved cross sections for excitation, ionization and charge transfer in collisions of hydrogen isotopes with protons, deuterons, tritons and the main fully stripped impurity ions.

Y. Wu, IAPCM, China, State-resolved cross section calculations for excitation, ionization and charge transfer in collisions between hydrogen neutrals and the principal fully stripped impurity ions.

C. Illescas, UAM, Spain, Theoretical studies of ionization, charge transfer and excitation in ion-H, He collisions in the energy range of 25-500 keV/amu.

Background to the Project

Fusion energy production relies on the reaction of hydrogen isotopes deuterium (D) and tritium (T) forming helium and releasing 14-MeV neutrons. In the magnetic confinement approach to fusion D-T plasma at a temperature of around 15 keV (about 17 million K) is trapped in a toroidal magnetic field inside a vacuum vessel. In a fusion reactor the high temperature in the core plasma will largely be maintained by the fusion reaction itself, but in present experiments external heating is required.

Injection of a beam of energetic neutral particles is one widely used method to heat the confined plasma and it is also intended to be used for power control in ITER and perhaps in a reactor. The beam particles must be neutral in order to penetrate the magnetic field, and they become ionized and thermalized due to interactions with the plasma electrons and ions. The neutral beam particles are normally the same as the main plasma species: H or D for a hydrogen plasma and He for a helium plasma. The particle energy for neutral beam heating ranges from about 100 keV for present experiments to 1 MeV foreseen for ITER.

Neutral beam injection is also an important tool for plasma diagnostics, which may rely on the heating beam or for which a dedicated diagnostic neutral beam can be used. Certain diagnostics, such as Beam Emission Spectroscopy (BES) and Motional Stark Effect (MSE) measurements are based on photoemission from the beam particles while Charge Exchange Recombination Spectroscopy (CXRS or CHERS) employs emissions from plasma impurities after a charge transfer collision with a neutral beam particle. For some applications diagnostic neutral beams of minority species are used, especially Li for measurements of edge plasma conditions.

Modelling of the beam penetration into the plasma and of the spectroscopic signals relies on detailed data for atomic processes that involve the neutral beam particles. In spite of the importance of the data there are quite significant gaps, especially related to processes starting from an excited state of the neutral atom. On the other hand, for processes starting from the ground state of the neutral atom there are often several different families of calculated or measured data, obtained using different approximations or experimental methods, and it is important to assess their uncertainties and to recommend best data.

Aims and Scope of the CRP

The CRP on Data for Atomic Processes of Neutral Beams in Fusion Plasma is meant to contribute to the development of fusion energy generation by providing trusted data for atomic processes relevant to neutral beam heating and neutral beam-based diagnostics of fusion plasma. It is intended that data produced, evaluated and/or recommended in the CRP will be used for interpretation of neutral beam-based diagnostics in fusion plasma experiments and will be used for modelling of neutral beam processes in present experiments and in preparations towards the operation of ITER.

The CRP aims to provide comprehensive evaluated and recommended data for processes of hydrogen (H, D, T) neutral beams in the high temperature core plasma. Low energy processes are out of scope. High energy collision processes in the hydrogen beam neutralizer and atomic processes of neutral beams of helium and lithium in the plasma are in scope inasmuch as the data development work has synergy with the core objective.

The CRP should provide data in as unprocessed a form as is reasonable in order to allow detailed kinetic modelling and to allow the development of applicable collisional-radiative models. Thus, for any collision process the CRP should provide density matrix elements or cross sections rather than rate coefficients; the user of the data can do the integration to obtain the rate coefficients for the relevant plasma conditions. Likewise, when a model provides state-resolved data then these are the primary output for the CRP; the user can do the appropriate averaging over incoming states and the sum over outgoing states when that is desired.

The relevant primary energy for neutral beam injection ranges from about 100 keV to 1 MeV and the relevant plasma temperature ranges from about 100 eV in the edge plasma to a few keV in the core plasma for present experiments and up to 20 keV in expected ITER operation; higher plasma temperatures, up to 40 keV, are created already in present experiments under special conditions. A heating or diagnostic neutral beam is surrounded by “halo” neutrals from charge exchange processes and these have a typical energy corresponding to the plasma ion temperature. Taking into account the halo neutrals the CRP should provide cross sections appropriate for neutral particle energies in the range of 1 keV to 1 MeV. For collisions with electrons, taking into account a high-energy tail on the Maxwellian, the CRP should provide cross sections for electron energies in the range of 100 eV to 100 keV.

CRP Tasks and Research Objectives

Specific project tasks and objectives are:

The objectives of the CRP include uncertainty assessment and evaluations of the propagation of uncertainties in atomic data to plasma simulations. In the specific research objectives each set of data development objectives is preceded by a sensitivity assessment of typical uses of the atomic data to uncertainties in those data. This will help to prioritize data development and evaluation activities.

Related Activities

The earlier CRP F43019 on Atomic and Molecular Data for State-Resolved Modelling of Hydrogen and Helium and Their Isotopes in Fusion Plasma (2011-2016) (short title: Hydrogen and Helium) is concerned with data for atomic and molecular processes of hydrogen and helium in the low temperature region close to the walls of the confinement vessel in fusion experiments. In the Hydrogen and Helium CRP molecular processes are of primary importance and the energy range of most interest is in the vicinity of 1 eV to 10 eV for all species. This is quite different than the focus in the Neutral Beams CRP F43023 on atomic processes at energies from 1 keV to 1 MeV for beam particles and 100 eV to 100 keV for electrons.

The Atomic and Molecular Data Unit has an active programme of meetings on uncertainty assessment, data evaluation and benchmark experiments. Larger meetings in that series include:

One or more small focussed data evaluation meetings may be organized in conjunction with the CRP to provide recommended data and uncertainties for a suitable subclass of processes.