Brighter and Shorter: LCLS configuration setups and diagnostics for super short pulses

Speaker: Nora Norvel

Time: 12:30pm September 21st, 2016

Location: SUSB 3002

Abstract

A typical scientist that wants to look at a protein would crystalize their sample, book some time at a lab, such as SSRL, and collect diffraction patterns to 3D image their previously mysterious protein. However, what happens when we want to look at really small things that can't be crystallized? This predicament was one of the driving forces behind the scientific need for Free Electron Lasers, specifically LCLS, that produces brighter, shorter X-Ray pulses. Members of the Single Particle Imaging (SPI) Initiative are trying to look at things on the edge of life, such as single celled organisms, organelle and viruses. In order to do this, injectors drop the sample into the beam line (sometimes living!) and the X-Ray pulses must be sufficiently bright and short to 'diffract before destruct'. How do we set up the machine to get these short pulses to ensure proper imaging? Turns out, LCLS has a lot of ways to do this! We have a nominal bunch compression scheme for everyday running but LCLS has several different methods to get down into the single digit femtosecond pulse duration that directly support the SPI goal. We heavily rely on the X-Band transverse cavity, or XTCAV, diagnostic that can measure the photon pulse width from the 'parent' electron pulse to determine the effectiveness of different pulse shortening methods. The XTCAV ensures operations delivers a beam that can get an accurate diffraction pattern before blowing up the sample.