In a significant advancement for fusion energy research, scientists have developed a novel method to enhance the transport of high-current negative ion beams, a critical component for plasma diagnostics in fusion reactors. This breakthrough, published in the journal *Nuclear Fusion* (translated to English), could have far-reaching implications for the energy sector, particularly in improving the efficiency and accuracy of plasma diagnostics.
The study, led by Dr. M. Nishiura of the National Institute for Fusion Science and the University of Tokyo, focuses on mitigating space-charge effects that often degrade the transport efficiency of heavy-ion beams. Space charge refers to the electrostatic self-repulsion within a beam of charged particles, which can cause the beam to diverge and lose intensity. This is particularly problematic for heavy ions like Au⁻, which are essential for heavy-ion beam probe (HIBP) systems used in magnetically confined fusion plasmas.
Dr. Nishiura and his team employed an innovative approach by optimizing the voltage allocation in a multistage acceleration system, effectively creating an electrostatic lens effect. This method suppresses space-charge-induced beam divergence and loss without requiring mechanical modifications to the beamline. “By carefully tuning the voltages, we were able to significantly improve the beam transport efficiency,” Dr. Nishiura explained. “This allowed us to increase the Au⁻ beam current injected into the tandem accelerator by a factor of 2–3.”
The results were validated through numerical simulations using the IGUN software and experiments conducted with the Large Helical Device-HIBP system. The optimized configuration enabled plasma potential measurements to be extended to higher-density plasmas, reaching line-averaged electron densities up to 1.75 × 10¹⁹ m⁻³ with an improved signal-to-noise ratio. “This technique offers a compact, practical, and highly effective solution for transporting high-current heavy-ion beams under space-charge-dominated conditions,” Dr. Nishiura added.
The implications of this research extend beyond plasma diagnostics. The method is broadly applicable to a wide range of accelerator systems, including those used in scientific and industrial applications where high-intensity beam transport is required. For the energy sector, this could mean more accurate and efficient diagnostics for fusion reactors, leading to better understanding and control of plasma conditions.
As fusion energy continues to be a promising avenue for clean and sustainable power, advancements in diagnostic technologies are crucial. This research by Dr. Nishiura and his team represents a significant step forward, potentially shaping the future of fusion energy research and development. The study not only enhances our ability to diagnose plasma conditions but also paves the way for more efficient and effective accelerator systems across various industries.