LBNL, Berkeley, California
LLNL, Livermore, California
The versatility of the beams that ECR ion sources can provide make them the injector of choice for many heavy ion accelerators. However, the design of the LEBT* systems for these devices is challenging because the LEBT has to be matched for a wide variety of ions. In addition, due to the magnetic confinement fields, the ion density distribution across the extraction aperture is inhomogeneous and charge state dependent, and the ion beam is extracted from a region of high axial magnetic field, which adds a rotational component to the beam. In this presentation a simulation model for ECR ion source beams is described. The initial conditions (i.e., spatial and velocity distribution of the ions prior to extraction from the ion source) are obtained semi-empirically. Extraction from the plasma is then simulated with the particle-in-cell code WARP. The same code is used for the actual simulation of ion transport through the beam line. Simulations of a beam containing uranium ions of charge state 18+ to 42+, as well as other ions due to the use of support gases, extracted from VENUS**, are presented and compared to emittance measurements.
LBNL, Berkeley, California
University of Applied Sciences Karlsruhe, Karlsruhe
Two ECR* ion sources are currently available to inject beams into the 88-Inch Cyclotron at LBNL.** The recently commissioned pepper-pot emittance scanner at LBNL was used to measure the beam emittance for various ion species of both sources. A pepper-pot scanner is capable of extracting the full four-dimensional transverse phase space of the beam, allowing for the calculation of the cross coupled emittances xy' and yx'. This is especially of interest for ECR ion sources where asymmetric beams are extracted in the presence of a strong solenoid field. The axial field adds a rotational momentum to the extracted beam, resulting in a transverse emittance growth, which depends on the magnetic stiffness of the extracted species. In this paper, the pepper-pot setup is described and emittance data from both LBNL ECR sources are presented and compared. The data confirm a strong mass dependence of the normalized emittance for ions with the same mass to charge state ratio as previously also measured by other groups. This dependence indicates a different particle distribution at the extraction aperture for different ion species.