"SPECIAL PLASMA SEMINAR: Laser-driven x-ray sources for high energy density science"

 

 

 

To meet the increasing requirements of examining and understanding high energy-density (HED) science phenomena on extremely short space- and timescales, it is necessary to develop novel and accessible light sources. We are developing one of the most promising applications of laser-wakefield accelerators—betatron radiation—to probe HED plasmas with unprecedented time resolution. This unique broadband, collimated (<30 mrad) source of hard x-rays (1–100 keV), with sub-ps pulsewidths, is produced by electrons accelerated and wiggled in the wake of a high intensity laser pulse in a plasma. When a short laser pulse with an intensity I >  10¹⁸  W/cm²  is focused inside a plasma, the laser ponderomotive force expels the plasma electrons away from the strong intensity regions to form an ion bubble in the wake of the pulse. Electrons trapped at the back of this structure are accelerated and wiggled by the focusing forces to produce broadband, synchrotron-like radiation in the keV energy range. Studies have implied that betatron x-rays have a source size of a few microns, a divergence of less than 100 mrad, a pulse duration of less than 100 fs, and a broadband spectrum in the keV energy range. Betatron x-rays are also directly related to the electrons emitting them, and thus the radiative properties of the source can be a diagnostic of the LWFA acceleration process. We will review recent experiments performed on petawatt-class lasers Titan and Callisto at the LLNL Jupiter Laser Facility, the Astra-Gemini laser in the UK, and at the LCLS-MEC high power laser of the SLAC National Accelerator Laboratory. Applications will also be discussed for future experiments at the Linac Coherent Light Source and the National Ignition Facility.