Speaker
Description
X-ray Free-Electron Lasers (XFELs) provide intense femtosecond X-ray pulses. The peak brightness is often high enough to destroy a sample with a single X-ray pulse. With their short pulse lengths, XFELs are optimal sources for studying ultra-fast processes started by optical laser pumping or by sample mixing. Additionally, high-repetition rate XFELs such as European XFEL or LCLS II require fast sample delivery to avoid double illumination of the same sample or to replenish sample for each X-ray pulse. These unique properties of XFELs give rise to challenges in sample delivery. In this talk, we’ll introduce challenges and opportunities at XFELs with an emphasis of sample delivery methods.
An overview of liquid sample delivery will be given, we’ll discuss development of drop-on-demand technologies and special sample delivery such as high viscosity injection. For serial femtosecond crystallography (SFX) protein crystals in suspension are prepared and injected into the interaction region of XFELS. Especially for membrane proteins, the sample can be extremely viscous, requiring special high viscosity extruders. Scattering and spectroscopy experiments on solutions, on the other hand, have different demands and need specialized sample delivery methods such as liquid flat sheet injectors. Often, samples are difficult to obtain in large quantities. In this case, highly efficient sample delivery methods like drop-on-demand systems are required.
If samples are in solid state or can be mounted on surfaces or window structures, fixed target sample delivery can be used. This method allows excellent sample efficiency: with good pre-characterization, every target can be hit. However, fixed target sample delivery tends to be slow and can hardly reach megahertz repetition rates. Other sample delivery methods to be discussed include aerosol sample delivery.
