Generation of gas density transition for laser wake field acceleration

Abstract

Experimental researches on the interaction of ultrahigh intensity laser with plasma have been stimulated by the rapid developments of high power laser technology. High intensity laser can produce a wake field with high amplitude plasma waves by ponderromotive forces as the laser propagates through an underdense plasma. Ultrastrong electric fields associated with wake fields were propased as a method of electron acceleration and have been verified up to the electron energy of 100 MeV. There are several approaches for plasma-based particle acceleration, including laser wake field acceleration (LWFA), plasma wake field acceleration (PWFA) and so on. In order to overcome the electron injection problem, all-optical schemes were proposed.However, these optical methods require extremely accurate laser spatial and temporal overlap, which again leads to technical difficulties. Recently, Suk et al. 1 1 1 proposed a self-injection scheme using a sharp density transition. In their scheme, a number of background plasma electrons are trapped near a sharp, localized, downward density transition and accelerated in the wake field. The experiments to verify Suk's proposal is scheduled t o perform using the Table ,Top Tarawatt (T3) laser facility at KERI in Korea. In this paper, as a preliminary step, we present an experimental r e sult on the generation of gas density transition. We use a tungsten wire just above a jet of He gas to generate a spatial modulation of the gas density in the direction of the beam propagation. We used a Mach-Zendher interferometer to measure the gas density distribution. The fringe pattern in the plane of the gas jet is imaged onto a CCD camera. Second harmonic pulses from a NdYAG laser with the p S e width of 10 nsec w e~e used as a probe of the interferometer. Spatial and temporal distribution of He gas density from pulse gas jet will be presented and discussed in details.The laser wakefield accelerator has been focused to get high acceleration gradient. As a terawatt laser pulse goes through highdensity plasma, a strong wakefield is generated and electrons are accelerated to high energy owing to the longitudinal electric field of the wakefield within a short electron-plasma interaction length. In addition, it is known that plenty of electrons are injected fmm the background plasma when the wakefield passes through it. To investigate this electron self-injection mechanism and acceleration of sell-injected electrons, several laser wakefield accelerator experiment has been performed at Korea Electrotechnology Research Institute (KERI) and experimental results of the Self-Modulated Laser Wakefield Accelerator (SM-LWFA) will be presented in this work.chbkimBkeri.re.kr ghkimOkeri.re.kr 364

Effect of sharp vacuum–plasma boundary on the electron injection and acceleration in a few-cycle laser driven wakefield

“…In addition, it is possible to achieve such a density transition by selecting suitable knife edge to form shock wave in gas in future. [40,41]…”