<Research Overview>

Plasma is the fourth state of matter in which electrons and atomic nucleus are dissociated, and a variety of interesting nonlinear phenomena, such as chaos and solitons, can be observed in plasma. Knowledge of the fundamental properties of plasma is also important for the realization of “fusion power,” which will create the sun on earth, since the laws of physics are universal not only on our earth but also in the whole universe.

In this research, as shown in the following figure, a structure called the devil’s staircase was discovered in a plasma in which a periodic electric field as external force is applied to nonlinear waves that exhibit a chaotic state called ionization waves, and the waves are synchronized, repeating synchronization and desynchronization. The devil’s staircase, also called the Cantor function, is characterized by a flat region (laminar) and a repeating phase shift of 2π (burst).

Now, in the process of desynchronization, in which the system transitions from a synchronized state to an asynchronized state by varying the intensity and frequency of the external force, the system is considered to undergo a saddle-node bifurcation.

Focusing on the mean value <T_L> of the duration of the synchronized state (the laminar region of the devil’s staircase), it is found that there exists a the -1/2 power-law between the gap from the threshold of synchronization and <T_L>, a feature consistent with the type-I intermittency by chaos theory.

We hope that through this research we have contributed to the field of fundamental research in physics. This study was supported by the JSPS KAKENHI (Grant numbers JP20K03895 and JP23K03355).

<Figure information>

Devil’s staircase appearing in the time evolution of the phase difference between the chaos wave and the external force.

<Journal information>

Title: Devil’s Staircase and Power-Law due to Desynchronization in a Laboratory Plasma

Authors: Takao Fukuyama, Kojiro Noguchi, Hiroto Miyoshi

URL: https://doi.org/10.1093/ptep/ptaf024

Progress of Theoretical and Experimental Physics

(Oxford University Press on behalf of JPS, latest IF: 6.2, latest rank: Q1)