Experimental observation of electron beam focusing through plasma lenses

A comprehensive experimental study of focusing of relativistic electron beams with overdense and underdense plasma lenses is being conducted at the Beam Test Facility at LBNL. Short (15ps rms) electron bunches, from the 50 MeV LBNL Advanced Light Source injector are transported through laser produced plasmas. The electron beam spot size and divergence at the plasma lens is adjusted using quadrupoles. The plasmas are 1-5 cm long with densities of 10¹³-10¹⁴ cm^-3. By changing the laser intensity and shape, the plasma density and profile can be controlled. This allows for exploration of both the charge and current compensation regimes, by changing the ratio of the plasma wavenumber, k_p, to the electron beam size, σ_r. Experimental results on the production of plasma through two-photon UV ionization and electron beam diagnostics have been presented earlier. Here we present results from experimentally observed plasma focusing for overdense lenses in charge and current compensation regimes. Detailed interferometric results from the production of highly overdense plasmas are also discussed