Spectroscopic observation of super-Alfvénic field-reversed configuration merging process by mixing of tracer ions

D. Kobayashi, T. Seki, T. Asai, Ts Takahashi, J. Morelli, M. Inomoto, T. Takahashi, S. Dettrick, H. Gota

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1 Citation (Scopus)


Visualization of the collisional merging formation process of field-reversed configuration (FRC) has been attempted. In the collisional merging formation process, two initial FRC-like plasmoids are accelerated toward each other by a magnetic pressure gradient. The relative speed of the collision reaches several times the typical ion sonic speed and Alfvénic speed. The magnetic structure of the initial-FRCs is disrupted in the collision process, but the FRC-like magnetic structure is reformed in ∼30 μs after the collision. Magnetic reconnection should occur in this process; however, general theoretical models in magnetohydrodynamics approximation cannot be applied to this process because of the high-beta nature of FRC and super-Alfvénic/sonic relative speed. In this work, the spectroscopic observation of the collisional merging FRC formation was conducted to evaluate the timescale and geometry of merging. A slight amount of tracer element (e.g., helium) was mixed into one of two initial-FRCs. Mixing of the tracer did not cause serious adverse effects on the performance of the initial-FRC in the collision and merging processes. The collision and merging processes were visualized successfully and observed using a fast-framing camera with a bandpass filter. The timescale of merging and the outflow speed in the collisional merging process of FRCs were optically evaluated for the first time.

Original languageEnglish
Article number103526
JournalReview of Scientific Instruments
Issue number10
Publication statusPublished - 1 Oct 2022


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