7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Experimental discoveries of a variety of turbulent states of magnetic fusion
plasmaKatsumi Ida
National Institute for Fusion Sciencee-mail : ida.katsumi@nifs.ac.jp
Experimental discoveries of various turbulent states ofmagnetically confined plasmas in far non-equilibrium
states for the Subrahmanyan Chandrasekhar Prize aredescribed in this talk. The following five topics will bepresented.
1. Systematizing Experimental Studies of Varieties ofTurbulent States.
Systematic experimental studies of various transport
state have been reviewed [1,2,3] in an ongoing effort
to systematize the entire body of advanced
experiments on plasma turbulent transport and many
confinement modes, as seen in Figure 1. Recently,
new experimental insights into the long-standing issueof the 'hydrogen isotope effect' have been found. [4].
2. Experimental discovery of intrinsic rotation due toplasma turbulence.
It was discovered experimentally that an intrinsic It
was discovered experimentally that an intrinsic
toroidal flow could be created [5]. The essential
aspect of turbulent plasma transport that temperature
gradients give rise to momentum flow was made clear.
This discovery significantly contributed to therealization of fusion reactors, as plasma rotation plays
an essential role in steady-state tokamak reactors andsuppressing turbulence.
3. Discovery of a strong electric field in H-mode.
The realization of the H-mode was a breakthrough forfusion research. The strong radial electric field(theoreticallysuggested)wasexperimentally
discovered as the mechanism for its occurrence [6].
This became the foundation for subsequent H-mode
research. The elucidation of the mechanism, which
followed this experimental result, provided
confidence in the universality of H-mode
manifestation regardless of the device and strongly
supported the development of fusion reactors.
4. Experimental quantification of the relationshipbetween topology and transport.
Plasmas can be confined by nested magnetic surfaces
accompanied by magnetic islands (regions withdifferent topologies). The nature of transport withinmagnetic islands was observed experimentally [7].
The difference in transport properties due to topology
also affects the global properties of nested magneticsurfaces. This fundamental result improves our ability
to make predictions about the global properties ofnested magnetic surfaces.

5. Study of 'non-local transport' in plasmas.
Transport phenomena that diffusion models cannot
explain have been observed in experiments.
Phenomena in which a local gradient does notdetermine the transport flux are called nonlocal
transport. The essential phenomena observed invarious aspects, such as transport hysteresis, areformulated [8].
These discoveries have enhanced the value of plasma
physics as a modern physics discipline and significantly
contributed to the realization of fusion reactors.
References[1] K.Ida, Plasma Phys. Control Fusion 40 (1998) 1429
[2] K.Ida and J.Rice, Nucl. Fusion 54 (2014) 045001[3] K.Ida and T.Fujita, Plasma Phys Control Fusion 60(2018) 033001[4] K.Ida et. al., Phys Rev Lett. 124 (2020) 025002[5] K.Ida et. al., Phys Rev Lett 74 (1995) 1990
[6] K.Ida et. al., Phys Rev Lett 65 (1990) 1364
[7] K.Ida et. al., Phys Rev Lett 88 (2002) 015002[8] K.Ida et. al., Nucl Fusion 55 (2015) 013022

L-modeH-modeinternal transportbarriermagnetic island

Figure 1. Various states of toroidal flow (pink lines),
poloidal flow (black lines), turbulence (white lines), andtemperature distribution (blue to red) generated inside
the plasma. The high temperature areas are shown in red
and the low temperature areas in blue. There is anL-mode with low temperature (upper right), an H-mode
where the temperature rises rapidly in the periphery(lower left), an internal transport barrier mode where thetemperature rises rapidly in the center (lower center), anda magnetic island state where the temperature rise isblocked in the crescent (lower right).