Recent Study on the Fundamental Physics and Novel Applications of Helicon Discharge

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Abstract
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Helicon discharges are among the most efficient radio-frequency plasma sources, capable of producing high-density plasmas with very high ionization and strong magnetization. These characteristics make them attractive for a wide range of applications, including plasma processing, electric propulsion, and magnetic fusion. This talk will introduce recent progress of my group on the fundamental physics and emerging applications of helicon discharges. First, the transient formation of helicon plasmas is investigated using a self-consistent multiphysics model that couples electron transport, heavy-species dynamics, RF electromagnetic fields, and plasma chemistry. The simulations reveal a rapid ionization stage during startup and show how wave-field structures and power deposition evolve as the plasma density increases. Second, the physics of the blue-core transition—one of the most distinctive phenomena in helicon discharges—is examined experimentally in several devices. High-speed imaging and probe measurements reveal that increasing RF power drives transitions from conventional discharge modes into a strongly ionized blue-core state, accompanied by rotation reversal, radial density restructuring, and modified wave coupling. Third, the role of energetic electrons and the first quantitative study of bump-on-tail instability under helicon-relevant conditions are presented. Recent work on helicon-wave heating relevant to magnetic fusion and the concept of “plasma fibre”, a density-structured plasma channel capable of guiding RF waves through refractive confinement, will be also introduced.

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About the Speaker
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Lei Chang is Associate Professor in School of Electrical Engineering at Chongqing University, where he holds joint appointments with Institute for Nuclear Energy Technology Innovation. He received Ph.D. in plasma physics from Australian National University in 2014. Chang’s research focuses on helicon plasma physics and applications, magnetic confinement fusion, and plasma-based space propulsion. His work spans theoretical plasma physics, numerical modelling, and the design and operation of magnetized plasma experiments. He has published over 50 papers. Chang is also active in the plasma science community, serving on several professional committees related to plasma physics and electric propulsion.