Title: Visualization of fast ion phase-space flow in plasmas well-below, near and well-above Alfvén eigenmode stability threshold in tokamak

Abstract

Abstract Transport of fast ions along certain local phase space paths, referred to as fast ion phase-space flow, has been systematically measured by an imaging neutral particle analyzer (INPA) in three plasma regimes, which are well-below, near, and well-above the Alfvén eigenmode stability threshold (Du et al 2021 Phys. Rev. Lett. 127 235002). (1) In plasmas well-below the Alfvén eignenmodes (AE) stability threshold, fast ions are well-confined on passing particle orbits without noticeable transport over the phase space. The observed INPA images agree well with the synthetic INPA images, using the fast ion distribution predicted by neoclassical theory. (2) In plasmas near the AE stability threshold, INPA images in the presence of AE activity moderately deviate from those without AE activity. The image difference can be well interpreted by AE-driven, phase-space fast ion flow. Paths of this flow over the velocity space (or streamlines) are reconstructed by the intersection lines of curved E ʹ and µ surfaces, referred to as E ʹ and µ line (where $E^{\mathrm{\prime }}\equiv E-\left(\omega /n\right)P_{\zeta }$ ; E , P _ζ and µ are the energy, canonical toroidal momentum and magnetic moment of ions; ω and n are the angular frequency and toroidal mode number of AEs, respectively). Resonant fast ions move radially inward by gaining energy and move radially outward by losing energy and the trajectory well aligns with the E ʹ and µ lines that pass through the mode resonances near the injection energy of neutral beams. (3) In plasmas well-above the AE stability threshold, fast ion phase-space dynamics shows additional features. Fast ions are transported out of the birth positions so promptly along the streamlines that the slowing-down process from the injection energy is not observable, exhibiting strong critical gradient behavior at local phase space. As a result, the increase of electron temperature is very small, in spite of an increase of beam power by $\sim 45\mathrm{\%}$ . It should be emphasized that the directions of phase-space transport, induced by AEs with different frequencies, structures and mode numbers, do not largely differ.

Authors:

Du, X. D. ;

• Search DOE PAGES for author "Du, X. D."
• Search DOE PAGES for ORCID "0000-0001-6127-2825"

Heidbrink, W. W. ;

• Search DOE PAGES for author "Heidbrink, W. W."
• Search DOE PAGES for ORCID "0000-0002-6942-8043"

Van Zeeland, M. A. ;

• Search DOE PAGES for author "Van Zeeland, M. A."
• Search DOE PAGES for ORCID "0000-0002-7911-2739"

Gonzalez-Martin, J. ;

• Search DOE PAGES for author "Gonzalez-Martin, J."
• Search DOE PAGES for ORCID "0000-0002-3237-5195"

Austin, M. E.; Yan, Z.; McKee, G. R.

• Search DOE PAGES for author "McKee, G. R."
• Search DOE PAGES for ORCID "0000-0002-2754-9816"

Publication Date:

Wed Mar 08 00:00:00 EST 2023

Research Org.:

General Atomics, San Diego, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1960338

Alternate Identifier(s):

OSTI ID: 1958684; OSTI ID: 1960433

Report Number(s):

DOE-GA-54698
Journal ID: ISSN 0029-5515

Grant/Contract Number:  

AC02-05CH11231; 5 AC05-00OR22725; FC02-04ER54698; SC0020337; AC05-00OR22725; AC02-09CH11466; SC0015878

Resource Type:

Published Article

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Name: Nuclear Fusion Journal Volume: 63 Journal Issue: 4; Journal ID: ISSN 0029-5515

Publisher:

IOP Publishing

Country of Publication:

IAEA

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; wave particle interaction; energetic particles; tokamak