Plasma accelerator development using CO2 laser beat-wave.

我们尝试从300ps上升、350J输出的CO2激光器中获得双线振荡激光，以激发等离子体波的节拍波。利用双线激光在充气氢等离子体中激发相对论等离子体波。本项目的目的是通过这种等离子体波来加速注入的电子。(1)我们尝试在10.6和9.6微米的双线组合和10.6和10.3微米的双线组合下激发等离子体波。前一种组合的共振密度为1.1×10；；17；/cm^3，后一种组合为9×10；15；/cm^3。通过隧道电离，我们成功地在激光持续时间内产生了等离子体。(2)尝试了用YAG激光对等离子体波进行汤姆逊散射测量，得到了等离子体波的时间分辨振幅。从YAG振荡器输出的二次谐波光垂直于CO2激光轴线注入。利用光谱分析仪对扫描相机的侧面散射光进行了分析。对于单线激光注入，我们通过后向拉曼散射观察到了等离子体波。等离子体波在激光上升后仅在300ps内被激发，其幅度达到2%的密度微扰，可以将等离子体电子加速到20keV以上。我们正在测量双线注入CO_2激光对等离子体波的激发。(3)为了测量加速电子的能量，我们研制了一台变场磁场分析仪，可以探测0-30 MeV的电子。我们现在试图比较电子能谱与等离子体波幅度及其时间关系。

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.