Phase-space turbulence
Organized Session: Nov. 9th, 15:00am - 18:00am (JST)In this unit, motivated by the anomalous transport problem in magnetically confined fusion
plasmas, formulation of nonlinear wave-particle interaction in turbulent field is advanced. For
the fusion directed goal, roles of phase-space turbulence on anomalous transport areinvestigated. In high-temperature and low-collision fusion plasmas, particles are trapped in aphase of wave by which the wave potential is nonlinearly evolved and a structure forms in thephase-space (Fig. 1 left). The phase-space structure can couple with the real space plasma
profile, by which a free energy is released and the phase-space structure grows (Fig. 1 right) [1].
Stochastic overlapping and cascade of the phase-space structures are also possible, resulting inemergence of the so-called phase-space turbulence. Phase-space turbulence is considered toplay a role for driving anomalous transport in high temperature plasmas, involving enigmatictransport features, e.g., nondiffusivity, nonlocality, subcriticality, and others [2]. According tothose theoretical predictions, survey for possible phase-space structures and examination of
their contribution on plasma transport are experimentally conducted in this unit. In velocity
distribution function measurement with a sufficiently high resolution, it is necessary to spreadsignal into the velocity dimension, which lowers the signal intensity at a single detector bin. In
other words, signal intensity and measurement resolution are in a trade-off relation, whichmakes phase-space turbulence detection challenging.

Figure 1. Overview of phase-space structure formation.

This unit attempts to overcome those difficulties by utilizing cutting-edge velocity space
diagnostic systems recently being developed [3]. Perspective view of phase-space structures
provided by state-of-the-art kinetic plasma simulation strongly helps optimization of diagnostic
systems in surveying target turbulent phenomena. Electron scale phase-space structures are
known to emerge in low-temperature and low-density basic devices, such as Q-machine, andexperimental demonstration of those structures were performed previously [4]. Revisiting thoseclassic phase-space experiments with aids of present-day diagnostic and simulation technics
propel basic understanding of phase-space turbulence physics.
This session is organized as follows. Overall strategy of the unit activity is presented by Dr.
Tatsuya Kobayashi (NIFS). Current status and perspective of diagnostic development for thevelocity space measurement, using different diagnostic concepts, e.g., charge exchange
recombination spectroscopy, conventional and corrective Thomson scatterings, and verticalelectron cyclotron emission, is overviewed by Dr. Tokihiko Tokuzawa (NIFS). In the following
session, a basic theoretical background of the phase-space turbulence in fusion plasmas isreviewed by Dr. Maxime Lesur (University of Lorraine). Phase-space structure formation is ageneral phenomenon in collisionless plasmas, and is known to occur in systems other thanmagnetically confined fusion plasmas. Nonlinear characteristics vary in different plasma
systems, therefore comparing different cases is beneficial for a general understanding of thephase-space structure formation. As a first step, an overview of the nonlinear wave-particle
interaction in the laser wake-field plasma acceleration study [5] is given by Dr. Masaki Kando(KPSI, QST).
[1] P. W. Terry, P. H. Diamond, and T. S. Hahm, Physics of Fluids B: Plasma Physics 2, 2048
(1990).
[2] Y. Kosuga, S.-I. Itoh, P. H. Diamond, K. Itoh, and M. Lesur, Nuclear Fusion 57, 072006(2017).
[3] K. Ida, T. Kobayashi, M. Yoshinuma, K. Nagaoka, K. Ogawa, T. Tokuzawa, H. Nuga, andY. Katoh, Communications Physics, in press (2022)[4] K. Saeki, P. Michelsen, H. L. Pécseli, and J. J. Rasmussen, Physical Review Letters 42, 501(1979).
[5] T. Tajima and J.M. Dawson, Physical Review Letters 43, 267 (1979).

Time table:
15:00-15:30 Tatsuya Kobayashi (National Institute for Fusion Science)
15:30-16:00 Tokihiko Tokuzawa (National Institute for Fusion Science)
16:00-16:20 Break
16:20-17:10 Maxime Lesur (University of Lorreaine)
17:10-18:00 Masaki Kando (Kansai Photon Science Institute, National Institutes forQuantum Science and Technology)