• J. Kim, G. Kim, J. Kim, S.H. Yoo
  KERI, Changwon

Using the nonlinear interaction between the high power laser and the plasma, we can generate strong acceleration field, called the laser wake field acceleration. The plasma density is very crucial to generate high energy electron. In this work, we studied the effect of the plasma density structure on the accelerated electron energy. We used 20 TW, 40 fs laser system to generate the plasma wakefield. A gas jet was used as a target. The plasma density was controlled by the back pressure of the gas nozzle and measured by the interferometer. The accelerated electron energy was measured using the electron energy spectrometer with 0.5 T magnet. The bunch charge was measured integrated charge transformer (ICT). When the plasma density is uniform, 2×10¹⁹ cm^-3 we can generate 200 MeV electron beam with bunch charge 33 pC. The electron beam divergence was less than 5 degree. If there exists the downward density tramp, the electron energy is only 50 MeV. The PIC simulation also indicates that if there is density ramp structure, the electron is not accelerated well. In this presentation, the overall experimental and simulation results are presented.