LBNL, Berkeley, California
Funding: US Department of Energy contract No. DE-AC02-05CH11231, and NSF Grant 0614001
We discuss the design and current status of experiments to couple the THUNDER undulator to the Lawrence Berkeley National Laboratory (LBNL) laser wakefield accelerator (LWFA). Currently the LWFA has achieved quasi-monoenergetic electron beams with energies up to 1 GeV*. These ultra-short, high-peak-current, electron beams are ideal for driving a compact XUV free electron laser (FEL)**. Understanding the electron beam properties such as the energy spread and emittance is critical for achieving high quality light sources with high brightness. By using an insertion device such as an undulator and observing changes in the spontaneous emission spectrum, the electron beam energy spread and emittance can be measured with high precision. The initial experiments will use spontaneous emission from 1.5 m of undulator. Later experiments will use up to 5 m of undulator with a goal of a high gain, XUV FEL.
*W.P. Leemans et al., Nature Physics, Volume 2, Issue 10, pp. 696-699 (2006).
**C.B. Schroeder et al., Proceedings AAC08 Conference (2008).
LBNL, Berkeley, California
University of Nevada, Reno, Reno, Nevada
Funding: Supported by the Office of High Energy Physics of the U.S. DOE under Contract No. DE-AC02-05CH11231, and DARPA.
Laser wakefield acceleration experiments were carried out by using various hydrogen-filled capillary discharge waveguides. Self-trapping of electrons showed strong correlation with the delay between the onset of the discharge current and arrival of the laser pulse (discharge delay). By de-tuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. Several possible scenarios for the enhanced trapping will be discussed along with spectroscopy of the transmitted laser light and the discharge recombination light.
LBNL, Berkeley, California
Funding: US Department of Energy
Staging Laser Plasma Accelerators (LPA), which is necessary in order to substantially increase the electron beam energy, requires incoupling additional laser beams into accelerating stages. To preserve high accelerating gradient of LPA, it is imperative to minimize the distance that is needed for laser incoupling. Using a conventional mirror with PW-class lasers will require the incoupling distance to be as long as tens of meters due to limitations imposed by laser induced damage of the optic. In this presentation we will describe a new approach for the laser incoupling that is based on planar water jet plasma mirror. The plasma mirror can operate as close as few cm to the focus of the laser thus minimizing the coupling distance. Using a water jet instead of a solid target avoids mechanical scanning of the target surface as well as contamination of the vacuum by laser breakdown debris. Experimental results showing performance of the water jet plasma mirror will be presented and progress in staging experiments will be discussed
LBNL, Berkeley, California
Funding: Funded by the U.S. DOE Office of Science HEP including contract DE-AC02-05CH11231, and by DARPA.
A key issue in laser wakefield accelerators (LWFAs) is injection of electrons into the accelerating region of the wake. Typically electron beams have been self-injected into the wake in a highly non-linear process, and at a higher plasma density than that for an optimized guiding and accelerating structure. This in turn limits the electron beam energy and quality that can be achieved. In this talk it is shown that this coupling of injection and acceleration can be addressed for LWFA in a capillary discharge waveguide with the use of a gas jet embedded into the capillary to longitudinally tailor the electron density profile. Previous experiments without a gas jet have shown self-trapping and acceleration of electrons with energy up to 1 GeV [Leemans et al., Nature Phys. Vol. 2, 696, 2006]. By adding a gas jet in the capillary it has been shown that electrons can be trapped and accelerated to high-energy using plasma densities in the capillary lower than in previous experiments, and that use of this technique improved electron beam properties.
