• C. Kim, I.S. Ko
  POSTECH, Pohang, Kyungbuk
• N. Hafz, G.-H. Kim, H. Suk
  KERI, Changwon

Laser and plasma based accelerators have been studied for a next generation particle accelerator. Still, there are some problems to solve for real applications. For example, it has been observed that the accelerated electron beam from laser and plasma based accelerators has a 100% energy spread. Thus, the generation of small energy spread beam is an important issue in the laser and plasma based accelerator study. In this work, we introduce a method to control the energy spread. From a basic theory and simulation, it is found that the transverse electron distribution is changed from the Gaussian to a Maxwell-Boltzmann distribution and low energy electrons spread out more rapidly than high energy electrons as they propagate in vacuum. Thus, a small size collimator is installed to remove the small energy electrons and it is conformed that the small energy spread can be obtained from an experiment.

• N. Hafz, H. Suk
  KERI, Changwon
• D.-K. Ko, J. Lee
  APRI-GIST, Gwangju

This Communication describes a 2D-PIC simulation of a laser wakefield accelerator in which an ultrashort, petawatt-class laser is focused and propagated through an underdense preformed plasma. We are looking at the phase-spaces of a large number of background plasma electrons that are accelerated to very high energies by the laser-induced plasma bubble. The result shows the possibility of generating a GeV-level electron beam in a few millimeters plasma size. As a future work, we will use a 500 TW laser system, that is under construction at APRI-GIST in Korea, for laser-plasma based accelerator researches to which the current simulation is relevant.

• M.S. Hur, G.-H. Kim, H. Suk
  KERI, Changwon
• A.E. Charman, R.R. Lindberg, J.S. Wurtele
  LBNL, Berkeley, California

We present analysis and simulations of kinetic effects in the Raman pulse amplification in plasma. An ultraintense and ultrashort laser pulse is a very essential part in an advanced acceleration scheme using laser and plasma. To make strong pulses, a noble scheme of using Raman backscatter in plasma was proposed and has been studied intensively.* The Raman amplification in plasma does not have a restriction in material damage threshold. However, for the new amplifier to be a promising alternative of the CPA technique, more extensive studies on various issues are required. One of the fundamental issues is the electron kinetic effect such as particle trapping or wavebreaking. We present a theoretical analysis of the kinetic effect; a new kinetic term is derived to be added to the fluid model and the effect of the new term is verified by averaged-PIC (aPIC)** simulations. Various one dimensional and semi-two dimensional aPIC simulations of pulse amplification are presented. We discuss the future application of the Raman scheme to upgrading the laser pulse of the Center of Advanced Accelerator in KERI, which are currently 2 TW and 700 fs, into a few more TW and less than 100 fs.

*V. M. Malkin, G. Shvets, and N. J. Fisch, Phys. Rev. Lett. vol. 82, 4448 (1999).**M. S. Hur, G. Penn, J. S. Wurtele, and R. Lindberg, Phys. Plasmas vol. 11, 5204 (2004).

• G.-H. Kim, N. Hafz, H. Suk
  KERI, Changwon
• I. W. Choi, D.-K. Ko, J. Lee, T.J. Yu
  APRI-GIST, Gwangju