Experiment on Langmuir Wave Supercontinuum

ZongMau Lee^1*, Eiichirou Kawamori¹

¹Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan, Taiwan

* Presenter:ZongMau Lee, email:happyfat332@gmail.com

In our laboratory plasma experiment, we have successfully generated Langmuir wave supercontinuum (LWSC), a phenomenon characterized by the significant spectral broadening of an initial pump wave due to nonlinear interactions with the medium. This work was motivated by the intriguing prospect that Langmuir waves (LWs), which are electrostatic waves in plasmas, could exhibit supercontinuum generation, much like conventional optical supercontinuum (SC). LWs having finite amplitude can be described by nonlinear Schrödinger equation (NLSE), which describes conventional optical SC generation as well. Previous particle-in-cell simulations have indeed supported the theoretical predictions of LWSC generation in plasma environments [1]. To achieve this, we designed and implemented a low-energy electron beam injector with variable electron temperatures (~1.5-6 T_e) to excite high-frequency electrostatic waves (0.2~0.55 GHz) within magnetized plasmas. Our experimental results unequivocally confirmed the generation of LWSC. We observed significant spectrum broadening in the excited waves, and the coherence properties were found to be contingent on the beam's energy and intensity. Specifically, strong beam input resulted in high coherence spectrum broadening, while low coherence spectrum broadening indicated the presence of Langmuir wave turbulence (LWT). We also noted that the transition between LWSC and LWT was influenced by the strength of the seed waves.



[1] Eiichirou Kawamori, Physics of Plasmas 24, 090701 (2017).

Keywords: Langmuir wave supercontinuum, Plasmas, Langmuir wave , Langmuir wave turbulence