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Register a new userSpatial distributions of plasma potential and density in electron cyclotron resonance ion source
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The Numerical Advanced Model of Electron Cyclotron Resonance Ion Source (NAM-ECRIS) is applied for studies of the physical processes in the source. Solutions of separately operating electron and ion modules of NAM-ECRIS are matched in iterative way such as to obtain the spatial distributions of the plasma density and of the plasma potential. Results reveal the complicated profiles with the maximized plasma density close to the ECR surface and on the source axis. The ion-trapping potential dips are calculated to be on the level of ~(0.01-0.05) V being located at the plasma density maxima. The highly charged ions are also localized close to the ECR surface. The biased electrode effect is due to an electron string along the source axis formed by reflection of electrons from the biased electrode and the extraction aperture. The string makes profiles of the highly charged ions more peaked on the source axis, thus increasing the extracted ion currents.
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The three-dimensional particle-in-cell model NAM-ECRIS is used for investigation of how the DECRIS-PM Electron Cyclotron Resonance Ion Source is reacting to changes in the source magnetic configuration. The accent is made on changes in the magnetic field at the magnetic trap center, the minimum-B value. It is calculated that the optimal normalized value of the field is ~0.8, close to the experimental observations. The reasons for existence of the optimum are discussed. It is observed that the electron energies are increasing with the increased minimum-B values due to enhanced confinement of the energetic electrons in the plasma. Bumps in energy spectra of the radially lost electrons are observed and explained to be due to nonadiabatic losses of electrons.
We have performed a systematic study of the Bremsstrahlung emission from the electrons in the plasma of a commercial 14.5 GHz Electron-Cyclotron Resonance Ion Source. The electronic spectral temperature and the product of ionic and electronic densities of the plasma are measured by analyzing the Bremsstrahlung spectra recorded for several rare gases (Ar, Kr, Xe) as a function of the injected power. Within our uncertainty, we find an average temperature of ? 48 keV above 100W, with a weak dependency on the injected power and gas composition. Charge state distributions of extracted ion beams have been determined as well, providing a way to disentangle the ionic density from the electronic density. Moreover X-ray emission from highly charged argon ions in the plasma has been observed with a high-resolution mosaic crystal spectrometer, demonstrating the feasibility for high-precision measurements of transition energies of highly charged ions, in particular of the magnetic dipole (M1) transition of He-like of argon ions.
Important features of Electron Cyclotron Resonance Ion Source (ECRIS) operation are accurately reproduced with a numerical code. The code uses the particle-in-cell technique to model a dynamics of ions in ECRIS plasma. It is shown that gas dynamical ion confinement mechanism is sufficient to provide the ion production rates in ECRIS close to the experimentally observed values. Extracted ion currents are calculated and compared to the experiment for few sources. Changes in the extracted ion currents are obtained with varying the gas flow into the source chamber and the microwave power. Empirical scaling laws for ECRIS design are studied and the underlying physical effects are discussed.
Three-dimensional numerical model is developed and applied for studies of physical processes in Electron Cyclotron Resonance Ion Source. The model includes separate modules that simulate the electron and ion dynamics in the source plasma in an iterative way. The electron heating by microwaves is simulated by using results of modelling the microwave propagation in the plasma by the COMSOL Multiphysics software. Extracted ion currents and other parameters of the source are obtained for different gas flows into the source. It is observed that the currents are strongly influenced by ion transport in transversal direction induced by the plasma potential gradients. Impact of some special techniques on the source performance is investigated. Magnetic field scaling is shown to reduce the ion losses during their movement toward the extraction aperture, as well as use of the aluminum chamber walls and mixing of the working gas with helium.
Electron dynamics in Electron Cyclotron Resonance Ion Source is numerically simulated by using Particle-In-Cell code combined with simulations of the ion dynamics. Mean electron energies are found to be around 70 keV close to values that are derived from spectra of X-ray emission out of the source. Electron life time is defined by losses of low-energy electrons created in ionizing collisions; the losses are regulated by electron heating rate, which depends on magnitude of the microwave electric field. Changes in ion confinement with variations in the microwave electric field and gas flow are simulated. Influence of electron dynamics on the afterglow and two-frequency heating effects is discussed.
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