Speaker
Description
The negative ion source concept currently under development for the ITER neutral beam injector exhibits several design flaws, notably: (i) plasma asymmetry along the direction parallel to the ion extraction grid, caused by the transverse magnetic configuration inducing an electron drift (Hall current) that is intercepted by one of the lateral walls (Hall effect), [1, 2] and (ii) an excessively high plasma potential, which is believed to adversely affect beam divergence in the accelerator. The objective of this study is to propose a novel ion source concept that addresses these fundamental issues. This novel ion source termed ANIS (Advanced Negative Ion Source) is currently under development at Laplace.
The proposed approach is primarily based on modifying the magnetic field configuration to both eliminate the Hall effect (by closing the electron drift path – forming a closed, wall-free drift loop – and thereby removing plasma asymmetry) and control the plasma potential amplitude (and its gradients) using electrodes positioned at the magnetic mirrors in the discharge region, thereby influencing the energy distribution of negative ions and improving beam optics.
Experimental results obtained on ANISette, a reduced-scale prototype of ANIS with a custom-built magnetized RF source featuring a radial magnetic field configuration, will be presented alongside three-dimensional (3D) particle-in-cell (PIC) simulations. The magnetic field topology can be tuned using coils, enabling detailed parametric studies of plasma transport mechanisms. Our observations show that the plasma parameters – density, electron temperature, and plasma potential – exhibit axisymmetric and relatively flat profiles in the expansion chamber. Moreover, the plasma potential amplitude can be effectively controlled by biasing electrodes placed at specific locations along the wall in the ionization chamber.
[1] F. Gaboriau, R. Baude and G.J.M. Hagelaar, Appl. Phys. Lett. 104, 214107 (2014)
[2] G. Fubiani, L. Garrigues, G.J.M. Hagelaar, N. Kohen and J-P. Boeuf, New Journal of Physics 19, 015002 (2017)
| Email address | freddy.gaboriau@utoulouse.fr |
|---|---|
| Classification | H- and D- sources for fusion, accelerators and other applications |