Photo-ionized lithium source for plasma accelerator applications

A photo-ionized lithium source is developed for plasma acceleration applications. A homogeneous column of lithium neutral vapor with a density of 2/spl times/10/sup 15-3/ is confined by helium gas in a heat-pipe oven. A UV laser pulse ionizes the vapor. In this device, the length of the neutral vapor and plasma column is 25 cm. The plasma density was measured by laser interferometry in the visible on the lithium neutrals and by CO/sub 2/ laser interferometry on the plasma electrons. The maximum measured plasma density was 2.9/spl times/10/sup 14/ cm/sup -3/, limited by the available UV fluence (/spl ap/83 mJ/cm/sup 2/), corresponding to a 15% ionization fraction. After ionization, the plasma density decreases by a factor of two in about 12 /spl mu/s. These results show that such a plasma source is scaleable to lengths of the order of 1 m and should satisfy all the requirements for demonstrating the acceleration of electrons by 1 GeV in a 1-GeV/m amplitude plasma wake.