Description
Electron cyclotron resonance heating (ECRH) plasmas have been crucial in various aspects of plasma physics research and fusion reactor development. They have been widely utilized for plasma start-up, allowing efficient initiation of confined plasmas and for extending plasma operation durations by maintaining stable plasma conditions. Furthermore, ECRH is essential for plasma transport studies, providing valuable insights into energy and particle transport mechanisms, which are key to achieving steady-state operation in future fusion reactors such as those based on the stellarator and tokamak concepts [1, 2]. The ECRH system in Large Helical Device (LHD) has been extensively employed in plasma heating experiments as a conventional heating method and as an advanced high-density heating scheme using perpendicular injection techniques. These methods have been explored to optimize energy absorption and improve plasma confinement properties [3, 4].
For the extension of the existing ECRH system in LHD, preparations are underway for installing a new high-power gyrotron, which is scheduled to be operational starting from the LHD campaign in October 2025. The upgraded ECRH system aims to provide higher power and flexibility for experimental studies.
Beyond its role in plasma heating, the ECRH system has also played a role in plasma diagnostics: collective Thomson scattering diagnostics, which enable the measurement of ion velocity distribution function [5]. Electron cyclotron emission (ECE) diagnostics, including correlation-ECE, have been developed using the ECRH transmission lines for plasma turbulence research. Recent experimental and theoretical investigations have yielded physics results, and ongoing component developments continue to improve these diagnostic techniques’ precision and reliability.
In recent years, collaborative research using the LHD-ECRH system has expanded significantly. One notable example is a joint research project conducted with a start-up company, university, and international institute, which focused on developing and testing a 28 GHz gyrotron. This collaboration leveraged the ECRH system for transmission line tests and gyrotron conditioning, contributing to both the enhancement of LHD’s experimental capabilities and the broader advancement of gyrotron technology. These efforts align with the overarching goal of improving ECRH systems for future fusion reactors, ensuring efficient and reliable plasma heating and diagnostics.
References
[1]. O. Motojima et al. Phys. Plasmas 6 1843 (1999).
[2]. H. Takahashi et al. Nuclear Fusion 53, 073034 (2013).
[3]. T. Tsujimura et al. Nucl. Fusion 61, 026012 (2020).
[4]. M. Nishiura et al. APS Division of Plasma Physics Meeting Abstracts PP11.079 (2022).
[5]. M. Nishiura et al. Rev. Sci. Instrums 93, 053501 (2022).
