Exploring Electron-Scale Turbulence through D-band Microwave Measurement in Magnetized Plasma

Zongmau Lee^1*, Eiichirou Kawamori¹

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

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

Turbulence in magnetized plasmas governs energy and particle transport, fundamentally shaping the efficiency and stability of magnetic confinement systems [1]. Small-scale turbulent fluctuations can degrade plasma confinement by enhancing cross-field transport, while their regulation is essential for achieving sustained fusion conditions. In particular, electron-scale turbulence strongly influences both the edge and core regions, where fine-scale transport processes determine the overall confinement quality. Nonlinear coupling between electron- and ion-scale turbulence further modifies transport characteristics and can lead to complex, multi-scale interactions that determine global plasma behavior [2].
Using the Magnetized Plasma Experiment (MPX), a linear plasma device, we investigate the generation of electron-scale turbulence and its coupling to ion-scale fluctuations to provide insights into future turbulence control and confinement optimization. A D-band (110–170 GHz) microwave scattering system enables high-resolution detection of electron-scale fluctuations (k⊥ρₑ > 0.1) [3]. It integrates high-gain antennas, heterodyne detection, and spectral analysis to measure density and electric-field perturbations, wavenumber spectra, and energy-cascade features. The system adopts a coherent Thomson-scattering configuration, where the scattering angle θₛ is adjusted to probe selected wavenumber ranges.
Simultaneous low- and high-frequency diagnostics, combined with Electron Cyclotron Emission (ECE), provide complementary real- and velocity-space measurements. MPX produces helium plasma using a 2.45 GHz magnetron with Electron Cyclotron Resonance heating, achieving B ≤ 0.15 T, nₑ = 10¹⁶–10¹⁸ m⁻³, and Tₑ = 1–15 eV. Spectral analyses show that electron-scale turbulence can arise from ion-scale activity and may contribute to inverse cascades, indicating nonlinear multi-scale energy transfer.
This study establishes an experimental framework combining D-band microwave scattering and ECE diagnostics to explore the generation and coupling of electron-scale turbulence. By elucidating its role in cross-scale transport processes, this work advances understanding of plasma micro dynamics and supports the development of turbulence regulation strategies for improved confinement in fusion plasmas.
[1] F. Jenko et al., Phys. Plasmas 7, 1904 (2000).
[2] S. Maeyama et al., Nat. Commun. 13, 3166 (2022).
[3] H. Bindslev, Plasma Phys. Control. Fusion 35, 1615 (1993).

Keywords: Magnetized Plasma Experiment , turbulence , D-band (110–170 GHz) microwave scattering system