Speaker
Description
The ITER experiment will employ two Neutral Beam Injection (NBI) systems to achieve the
temperatures required for the deuterium-tritium fusion reaction to occur. Each injector relies
on a negative ion source, in which a low-pressure deuterium plasma is sustained by radiofrequency (RF) power through inductive coupling. The performance of the sources, in terms
of power coupling efficiency and plasma uniformity, depends critically on the dynamics of the
inductively coupled plasma (ICP). Understanding the impact of the ICP dynamics on the
source performance requires a self-consistent kinetic description that can capture plasma–
field interactions on the RF timescale.
In this work, a self-consistent inductive coupling model has been implemented in GPPIC, a
2D–3V Particle-In-Cell Monte Carlo Collisions (PIC–MCC) code written in C++/CUDA and
under development at Consorzio RFX. The code, originally electrostatic and 2D Cartesian,
has been extended to a 2D axisymmetric cylindrical geometry and developed to solve selfconsistently the electrodynamic part of Maxwell’s equations. This development enables the
kinetic study of low-frequency ICPs without relying on simplified power deposition models.
A central aspect of the study is the analysis of density scaling, a numerical technique
commonly adopted in PIC simulations to manage the high computational cost associated with
the kinetic description of high plasma density and volume. In this approach, the vacuum
dielectric constant in Poisson’s equation is artificially reduced, effectively representing a
plasma of lower density. The results demonstrate that such scaling alters the plasma response
to the external RF fields.
Although a fully stable solution has not yet been achieved, the developed code successfully
reproduces key features of low-frequency ICPs, such as plasma oscillations at twice the RF
frequency and ponderomotive plasma compression. Therefore, this work represents a crucial
step toward a self-consistent and kinetic description of RF plasma dynamics in negative ion
sources, directly supporting the optimization of the ITER NBI source.
