100 MeV Injector Cell for a Staged Laser Wakefield Accelerator

A 100 MeV electron laser wakefield injector based on a sub-millimeter gas cell is presented. The gas cell, used mainly to overcome the density inhomogeneity associated with gas jets, is capable of yielding a homogeneous plasma source with densities less than 2 × 1019 cm−3. Sharp step plasma density boundaries were obtained by using the laser to drill the gas cell pinholes as small as 100 μm in diameter. The gas cell lengths were comparable to the dephasing length. The gas cell length and density were varied to study electron bunch characteristics. The UCLA 10 TW Ti:Sapphire laser was focused into the gas cell where helium and hydrogen were used as target gases with a few percent nitrogen impurity added to induce ionization trapping of the electrons [1]. The observed electron beams had divergences less than 2 mR. A model for producing low divergence beams is presented.