Direct Measurement of Focusing Fields in Active Plasma Lenses

Author(s): Rockemann, J-H; Schaper, L; Barber, SK; Bobrova, NA; Boyle, G; Bulanov, S; Delbos, N; Floettmann, K; Kube, G; Lauth, W; Leemans, WP; Libov, V; Maier, A; Meisel, M; Messner, P; Sasorov, PV; Schroeder, CB; Tilborg, JV; Wesch, S; Osterhoff, J | Abstract: Active plasma lenses have the potential to enable broad-ranging applications of plasma-based accelerators owing to their compact design and radially symmetric kT/m-level focusing fields, facilitating beam-quality preservation and compact beam transport. We report on the direct measurement of magnetic field gradients in active plasma lenses and demonstrate their impact on the emittance of a charged particle beam. This is made possible by the use of a well-characterized electron beam with 1.4 mm mrad normalized emittance from a conventional accelerator. Field gradients of up to 823 T/m are investigated. The observed emittance evolution is supported by numerical simulations, which suggest the potential for conservation of the core beam emittance in such a plasma lens setup.