LCLS-II introduces MHz-rate operation and sub-femtosecond X-ray pulses, creating a need for high-rate control mechanisms at the photoinjector and diagnostic systems capable of extracting pulse structure on every shot. This work presents two key components toward meeting these requirements. First, a programmable photoinjector-laser system combining a spatial light modulator with dispersion-controlled nonlinear synthesis enables tunable UV temporal profiles compatible with the LCLS-II photocathode.* Beamtime measurements demonstrate controllable modulation of the electron bunch and corresponding structure in the emitted X-ray pulses, including a triple-hump temporal pattern. Second, a high-throughput streaming front-end and machine-learning framework is developed for the Multi-Resolution Cookiebox diagnostic to rapidly extract attosecond X-ray pulse structure at high repetition rate.** Together, these advances supply essential building blocks for future adaptive operation, including multiplexed experimental modes, live tuning of X-ray output, and integration with emerging modeling and optimization efforts.***

Next-generation XFELs require electron beams with reproducible current profiles, reduced longitudinal curvature, and stable compression behavior. At LCLS-II, we employ a hybrid programmable-laser architecture*: combining IR-domain programmable shaping with dispersion-controlled nonlinear synthesis (DCNS)**, to generate tuned flattop ultraviolet (UV) temporal profiles that reshape the longitudinal phase space upstream of collective effects. Using tens of picoseconds UV flattops, we obtain smooth, uniform, low-curvature current distributions at 80 pC. The shaping supports strong, linear compression and reproducible 1.9–2.0 kA peak currents without downstream re-optimization. These results establish source-level flattop shaping as a practical route to improved stability, compression tolerance, and brightness in MHz-class XFELs, and a flexible tool for future adaptive beam-delivery modes.

LCLS-II introduces MHz-rate operation and sub-femtosecond X-ray pulses, creating a need for high-rate control mechanisms at the photoinjector and diagnostic systems capable of extracting pulse structure on every shot. This work presents two key components toward meeting these requirements. First, a programmable photoinjector-laser system combining a spatial light modulator with dispersion-controlled nonlinear synthesis enables tunable UV temporal profiles compatible with the LCLS-II photocathode.* Beamtime measurements demonstrate controllable modulation of the electron bunch and corresponding structure in the emitted X-ray pulses, including a triple-hump temporal pattern. Second, a high-throughput streaming front-end and machine-learning framework is developed for the Multi-Resolution Cookiebox diagnostic to rapidly extract attosecond X-ray pulse structure at high repetition rate.** Together, these advances supply essential building blocks for future adaptive operation, including multiplexed experimental modes, live tuning of X-ray output, and integration with emerging modeling and optimization efforts.***

Electron dynamics in molecules occur on sub-femtosecond timescales and drive fundamental processes such as photosynthesis, catalysis, and chemical bond transformations. Attosecond XFELs provide the temporal resolution and pulse power necessary to probe these phenomena. Emerging superconducting accelerator technology further enables high-repetition-rate operation, enhancing statistical sensitivity of data while compressing measurement time. Here, we present the first direct temporal measurements of single-shot attosecond soft X-ray pulses driven by a continuous-wave high-repetition-rate accelerator. Using angle-resolving electron time-of-flight spectrometers, we perform angular streaking measurements with high energy and temporal resolution, allowing complete pulse reconstructions. These measurements showcase the attosecond science capabilities of LCLS-II at high repetition rates and provide the foundation for controlling and shaping x-ray pulses to study ultrafast dynamics in complex systems with precision.

High gradient radio frequency (rf) driven photoguns are photoemission electron sources that have important applications for accelerator-based instruments, such as light sources and electron microscopy. Numerous efforts have been made to push for even higher field gradient while suppressing rf breakdowns. We propose the Compressed Ultrashort Pulse Injector Demonstrator, a 1.6 cell photogun driven by nanosecond high power rf pulses to achieve high gradients with low breakdown rate. This photogun is powered by ultrashort pulses from a rf pulse compressor and a high power klystron. This presentation focuses on the work of the CUPID photogun for generating bright electron beams to drive x-ray free-electron lasers (FELs) at 40 keV photons or higher. We first show the design of CUPID photogun, followed by its capability of bright beam generation when forming a photoinjector with a superconducting solenoid and downstream linacs. We then show start-to-end simulations of the existing LCLS copper accelerator free-electron laser with CUPID photogun as a drop-in replacement to demonstrate its improvement in delivering hard x-rays at mJ level pulse energy. Finally, we show preliminary high power rf testing of CUPID prototypes and plans for electron beam generation.