Plasma accelerator development using CO2 laser beat-wave.

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We tried to obtain double line oscillation laser light from CO 2 laser of 300 ps rise and 350 J output for beatwave excitation of plasma wave. By using the double line laser we excited relativistic plasma wave in gas-puffed hydrogen plasmas. The purpose of this project is to accelerate injected electrons by this plasma wave.(1) We tried to excite the plasma wave both for double line combination of 10.6 and 9.6 mum and of 10.6 and 10.3 mum. The resonant density is 1.1x10^<17>/cm^3 for the former combination and 9x10^<15>/cm^3 for the latter. We succeeded to produce plasmas in the laser duration through the tunneling ionization.(2) We tried YAG laser Thomson scattering measurement of plasma waves, which enables us to obtain the time-resolved plasma wave amplitudes. A 2nd harmonic light from the YAG oscillator is injected perpendicularly to the CO2 laser axis. The side scattered YAG light are analyzed through spectrum analyzer to streak camera. For single line laser injection, we observed the plasma wave through backward Raman scattering. The plasma wave is excited only in 300ps just after the laser rise and its amplitude attains to 2% density perturbation, which can accelerate the plasma electrons more than 20 keV.We are now measuring the plasma wave excitation by double line injection CO2 laser..(3) To measure the accelerated electron energy, we developed a field variable magnetic analyzer, which can detect electron from 0 to 30 MeV.We try now to compare the electron energy spectrum with the plasma wave amplitude and its time dependence.