Tapering of plasma density ramp profiles for adiabatic lens experiments

One of the key elements of the plasma wakefield blowout regime is the strong, linear focusing provided by the ion density. One advantage of this focusing is its extraordinary strength whose gradient is proportional to the local background plasma density, that is particularly important for adiabatic focusing schemes in future compact linear colliders. Local plasma density variations can be obtained in gas-filled capillaries by varying monotonically the diameter of the capillary. Here we present the ongoing study of the plasma density profile obtained for different tapering angles of the capillary shape and we discuss their use for the adiabatic plasma lens experiment proposed at SPARC_LAB