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.
