Researchers have demonstrated that controlling the electric potential within fusion-grade plasma is vital for sustaining energy confinement in nuclear fusion reactors. The team used a heavy ion beam probe with negatively charged gold ions to measure the internal plasma potential in the Large Helical Device.
By accelerating and injecting gold ions into the plasma, scientists observed the charge-state transitions needed to infer high-precision electric potential values. This technique depended on a stable, intense ion beam. Despite improvements in negative ion sources, efficiently injecting high-current beams into the tandem accelerator limited diagnostic accuracy.
Simulations revealed that heavy ion beams suffered significant losses at high currents due to space-charge effects, which expanded the beam and reduced transport efficiency. Researchers optimized voltage allocation across multistage accelerator electrodes, using them as electrostatic lenses. This strategy achieved a transmission rate exceeding ninety-five percent, greatly enhancing beam injection efficiency.
Plasma experiments confirmed these results, with injection currents increasing up to three times. The enhanced measurements allowed scientists to track rapid shifts in plasma potential as energy confinement states changed, such as after the termination of electron heating and subsequent neutral beam injection. These results provide foundational data for future fusion reactor design and plasma control models.
The method offers a practical workflow for optimizing beam transport and diagnosing reactor-grade plasmas with reproducible precision. Its applications extend to other diagnostic systems requiring high-intensity ion beams.
Research Report:Enhanced beam transport via space charge mitigation in a multistage accelerator for fusion plasma diagnostics
