In magnetized plasmas, many dynamical processes affect the ion velocity distribution function, both in laboratory and astrophysical environments. Measurements of this quantity can give useful insights for the study of phenomena such as magnetic reconnection, ion heating and acceleration, and turbulence. For this purpose, we designed a new diagnostic system that evaluates the ion velocity distribution function at the edge of fusion plasmas. The proposed device, called DIVO (Diagnostic for Ion Velocity Observation), resolves the two components of the ion velocity, parallel and perpendicular to the magnetic field. DIVO will be mounted at the plasma edge in the RFX-mod2 experiment, a Reversed-Field Pinch device, that has been upgraded for operation in 2026. DIVO offers a direct and local measurement that will enhance our knowledge on the thermal and supra-thermal ion populations at the plasma edge, as RFX-mod was not equipped with any instrument able to evaluate locally the ion distribution functions in velocity space. The working principle of this diagnostic system is based on the force balance between the electric and the Lorentz force, with the aim of interrupting the Larmor gyration of the ions, which is associated with the velocity component perpendicular to the magnetic field. Since the balance depends on the ion’s perpendicular velocity, a specific externally applied electric field allows for the selection of ions with within a given range, while is evaluated by the ion’s impinging position on a matrix of detectors. The instrument is equipped with a series of parallel thin metallic plates that filter the incoming ions, improving the resolution of the system. Individual particle simulations using Boris algorithm have been performed to optimize the instrument design and performances, assess its expected velocity resolution and operational range, and evaluate the transmission function needed to convert the detected counts into the original distribution function of the ions.
磁化プラズマ中では、多くの動的過程がイオン速度分布関数に影響を及ぼす。これは実験室および天体物理環境の両方においてである。この量の測定は、磁気リコネクション、イオン加熱・加速、乱流などの現象の研究に有用な知見をもたらす。この目的のため、我々は核融合プラズマの周辺部におけるイオン速度分布関数を評価する新しい診断システムを設計した。提案する装置DIVO（Diagnostic for Ion Velocity Observation）は、イオン速度の磁場に平行および垂直な二つの成分を分解する