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The peak power of 30 TW and the pulse width of 1 ps produced by the Nd:glass laser system is capable of creating a highly-ionized plasma of a moderate density gas on an ultrafast time scale and generating a large amplitude plasma wave with an accelerating gradient of the order of GeV/m. We are going to demonstrate particle acceleration, injecting electrons of a few MeV emitted from a solid target by intense laser irradiation. >

A collinear wakefield test facility using two linacs with a common test section is constructed. Beams from one linac excite wakefields in a test medium such as a plasma, while beams from the other linac witness the wakefields. The time interval between the two beams is controllable with an accuracy of /spl sim/1 psec. Plasma wakefield acceleration and plasma lens experiments were conducted using this facility. >

Experiments of plasma wakefield acceleration driven by narrow bunches were performed in the overdense regime at the University of Tokyo. Changes of energy and beam size of the test bunches caused by the driven bunches were observed. An acceleration gradient of about 1 MeV/m was observed.