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

A review of phase space turbulence: why it is important
Y. Kosuga
RIAM, Kyushu Univ.
e-mail (speaker):kosuga@riam.kyushu-u.ac.jp
An interesting and important aspect ofinstabilities. While driving fluctuations, phase space

turbulent plasmas is the role of phase space. Unlike usualstructures also excite meso-scale zonal flows[3]. Zonal

fluid turbulence, phase space (or in particular, theflows set a limit on the maximum amplitude of drift

velocity space) plays important role in dynamics. Aholes. They also reduce transport. In addition toclassic example is of course the wave-particle interaction,

conventional turbulence suppression, zonal flows reduceand the excitation and the damping of waves can happen

transport by phase space structures by exerting

via the resonance with particles in plasmas. The phase

dynamical friction on these structures.

space can be a key to understand various phenomena

Recent developments in experiments allow

including, but not limited to, acceleration of particles,

us to directly measure the distribution function[4]. Whilecoronal heating, etc. In more practical matters, they are aearly experiments on the wave-particle interaction

key for the success of magnetically confined plasmas.

measured the role of phase space indirectly by observing

The purpose of this talk is to present thedamping length of the mode in tubes, recent experiments

current status of the subject and to discuss futurereport the direct observation of the deformation of thechallenges. Then, in this talk, we will start by

distribution function. Thus now it is possible to identify

discussing what we know, or at least we think weturbulence activity in the distribution function. In thisunderstand, about the subject.

talk, we will discuss a possible target to identify theIn this part, we will lookat the simplest example of phase space turbulence infootprint of phase space turbulence, by using coherent

unmagnetized plasmas. This simple example is used todrift holes as a typical example.

introduce relevant ingredients in phase space turbulence,

This work is based on the collaboration withsuch as phase space coherent holes[1], phase spaceP.H. Diamond, K. Itoh, T.S. Hahm, K. Ida, S. Inagaki, T.

granulations[2], etc. We will also briefly describe how

Kobayashi and we acknowledge the various inputs. This

these elements impact transport through dynamical

work was partly supported by Grants in Aidsfrictions.

(KAKENHI) of JSPS, Japan (21H001066), Joint
Then we discuss application to magneticallyResearch Program of RIAM, Kyushu University.

confined plasmas. In particular, we show how thesephase space structures impact confinement of plasmas. A
simplified drift wave is used as a typical example andcharacteristic structures such as drift holes, granulations,
are introduced. Once formed, these phase spacestructures can tap free energy even when underlying drift
waves cannot. This results in explosive subcritical

References[1] T.H. Dupree Phys. Fluids 25 277 (1982)[2] T.H. Dupree Phys. Fluids 15 334 (1972)[3] Y. Kosuga, S.-I. Itoh, P.H. Diamond, K. Itoh, Nucl.
Fusion 57 (2017) 072006[4] K. Ida, et al., Commun. Phys. 5 228 (2022)