Speaker
Description
The custom Particle-in-Cell code we are developing for the study of Electron Cyclotron Resonance Ion Sources (ECRIS) has reached a version that reproduces various experimental observations. It also explained why the HSMDIS[1] magnetic configuration shows no erosion of the Boron-Nitride disks. The code reproduces the plasma formation from an empty plasma chamber to a density of the order of 1E17 m^-3, including the beam extraction up to tens of mA. Disclosing the close relation between plasma properties and beam properties. We were able to disclose the different behaviour produced by two different magnetic configurations of the 2.45GHz ECR ion source: the standard[2] and the HSMDIS[1]. Results show that the standard magnetic configuration can heat the plasma even without active ECR resonance within the plasma chamber, and that the HSMDIS magnetic configuration uses the ECR and UHR resonances to heat, confine, and stabilize the plasma. The formation of electrostatic waves was also disclosed in two regions of the CMA diagram, and their role in plasma density displacement was clarified. The code is written in Matlab, with a live link to Comsol for the computation of the magnetostatic and electromagnetic fields, while different mex functions written in C and parallelized with OpenMP compute the motion and interactions of the species. In solving the Poisson problem, we note that the space-charge density variation affects only the known term in the system of linear equations that discretize the problem. We use this peculiarity to factorize (the most computationally intensive part) only once, and then solve the simplified system whenever needed. We also minimized the number of solutions, considering the value of the rising plasma frequency. Many other optimization strategies were adopted to make the computation efficient, a highly crucial aspect for enabling the study of plasma evolution over hundreds of microseconds with a time step of 2E-12 seconds. While the implementation of plasma interactions with metallic and insulating materials, including secondary electron emissions, is satisfactory, we have evidence that the hydrogen chemistry needs to be enriched with the formation of hydrogen molecular excited states and negative hydrogen ions. The ongoing development ot the three-dimensional Poisson solver (with GPU implementation) and the enrichment of chemical reactions will also enable the simulation of negative hydrogen ion sources.
[1] L. Neri, et al., "HSMDIS PERFORMANCE ON THE ESS ION SOURCE" in Proc. 31st Linear Accelerator Conf. (LINAC'22), Liverpool, UK, Aug.–Sep. 2022, pp. THPORI19. JACoW Publishing, doi:10.18429/JACoW-LINAC2022-THPORI19
[2] Taylor, T. & Wills, J. S. C. (1991) "A high-current low-emittance dc ECR proton source", Nuclear Instruments and Methods in Physics Research Section A, 309 (1-2), 37-42.
