Events at Physics
tools for many fields of science. They are used for biology, material science, medicine, or industry. Such
sources rely on conventional particle accelerators, where electrons are accelerated to gigaelectronvolts
(GeV) energies. The accelerating particles are also wiggled in magnetic structures to emit x-ray radiation
that is commonly used for molecular crystallography, fluorescence studies, chemical analysis, medical
imaging, and many other applications. One of the drawbacks of synchrotrons and XFELs is their size and
cost, because electric field gradients are limited to about a few 10s of MeV/M in conventional
This seminar will review particle acceleration in laser-driven plasmas as an alternative to generate x-rays.
A plasma is an ionized medium that can sustain electrical fields many orders of magnitude higher than
that in conventional radiofrequency accelerator structures. When short, intense laser pulses are focused
into a gas, it produces electron plasma waves in which electrons can be trapped and accelerated to GeV
energies. This process, laser-wakefield acceleration (LWFA), is analogous to a surfer being propelled by
an ocean wave. Betatron x-ray radiation, driven by electrons from laser-wakefield acceleration, has
unique properties that are analogous to synchrotron radiation, with a 1000-fold shorter pulse. This source
is produced when relativistic electrons oscillate during the LWFA process.
An important use of x-rays from laser plasma accelerators we will discuss is in High Energy Density
(HED) science. This field uses large laser and x-ray free electron laser facilities to create in the laboratory
extreme conditions of temperatures and pressures that are usually found in the interiors of stars and
planets. To diagnose such extreme states of matter, the development of efficient, versatile and fast (subpicosecond
scale) x-ray probes has become essential. In these experiments, x-ray photons can pass
through dense material, and absorption of the x-rays can be directly measured, via spectroscopy or
imaging, to inform scientists about the temperature and density of the targets being studied.
Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory
under contract DE-AC52-07NA27344, supported by the LLNL LDRD program under tracking code 13-LW-076,
16-ERD-024, 16-ERD-041, supported by the DOE Office of Fusion Energy Sciences under SCW 1476 and SCW
1569, and by the DOE Office of Science Early Career Research Program under SCW 1575.