Special Issue "Neutral Atoms in Controlled Fusion and Space Plasmas"
A special issue of Atoms (ISSN 2218-2004).
Deadline for manuscript submissions: 31 December 2021.
Interests: plasma physics; mathematical modelling of plasma; diagnostics of high-temperature plasma; atomic and nuclear processes in plasma
Interests: plasma physics; plasma-material interaction; radiation damage; fundamental atomic and molecular data; databases; data management
Interests: Plasma-material/plasma-wall/plasma-surface interactions; edge plasma physics; atomic and molecular processes in edge plasmas; irradiation-induced damage; core plasma physics; hydrogen processes; multi-scale modelling
Techniques dealing with fluxes of fast suprathermal neutral particles in plasma are at the frontier of controlled fusion research and space exploration. Neutral beam injection (NBI) is currently the main method for heating fusion plasmas in flagship magnetic confinement devices. Neutral particle analysis (NPA) is the most direct method for diagnosing fast ions in a magnetically confined fusion plasma by detecting the escaping neutral atoms formed of these ions due to charge changing atomic reactions. In astrophysics and planetary science, measurements of this kind are typically referred to as energetic neutral atom (ENA) imaging or sensing of space plasmas.
NBI systems based on positive ion sources are suitable at beam energies around 150 keV or lower. To produce higher energy beams at 500 keV or above, required for enhancing fusion plasma performance, negative ions are used to maintain an optimum neutralization fraction. NBI at 1 MeV for D0 beams based on a negative ion source is one of the basic systems required to reach ITER operation goals . The deuterium NBI is the most powerful heating system at JT-60SA, including both positive ion-source-based injection at 85 keV and negative ion-source-based injection at 500 keV .
Numerical modeling of NBI and the related diagnostics certainly require the knowledge of cross-sections of all relevant atomic reactions. It is noted, first, that many of the required cross-sections are not well defined, with uncertainties of over 10%, second, that the lack of experimental data in energy regions of interest necessitates some of cross-sections to be extrapolated, and third, that fewer data are available for explicit deuterium reactions; thus, protium cross sections are used .
The main NPA purpose on ITER is to measure the deuterium/tritium fuel isotope ratio in the plasma core using energy distributions of escaping D0 and T0 atoms in the MeV range . Advanced NPA diagnostics in the MeV energy range were used on JT-60U  and are foreseen at JT-60SA . Measurements of kinetic energy resolved fluxes of neutral hydrogen and helium atoms are possible. Thus, cross-section data are required for all the atomic reactions that lead to a change of the electric charge state of hydrogen and helium particles in plasma in the presence of impurities. These reactions determine both the source function of neutral atoms within the plasma and the attenuation of the neutral flux in the plasma between the birth location and the periphery. The attenuation of the neutral flux from plasma towards the NPA diagnostic device is governed by the same physics as the penetration of fast atoms from the NBI into plasma.
ENA sensors provide information on composition, spatial, temporal, and energy distributions of plasma particles around the Earth and other planets, at the heliospheric boundary, and in the interstellar medium [7,8]. Analogously, ENAs originate from energetic ions through charge-changing collisions with the constituents of the ambient space plasma of interest.
This Special Issue is dedicated to all aspects of atomic physics, atomic, and molecular data and numerical modeling involved in the development of NBI, NPA, and ENA systems, as well as in theoretical and experimental research work associated with these systems. The purpose is to facilitate the tasks of plasma and fusion scientists. Review articles, original research articles, and data tables are welcome, aiming to extend the renowned sources such as  and the subsequent volumes  and further develop the approach [11,12]. In addition, multidisciplinary papers illustrating the importance of the subject in both plasma physics and astrophysics would be of interest.
 Atomic and Plasma–Material Interaction Data for Fusion No. 1, IAEA, Vienna (1991)
 Atomic Data for Fusion, vol. 1, ORNL-6086 (1990)
Dr. Pavel Goncharov
Dr. Christian Hill
Dr. Kalle Heinola
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- Neutral beam injection
- Neutral particle analysis
- Energetic neutral atoms
- Atomic data for fusion
- Diagnostics and modeling of fusion plasmas
- Remote sensing of space plasmas