We list potential tuning knobs for optimizers and gather ideas on automatic FEL tuning.
Tuning knobs/potential optimization loops:
- Adaptive orbit feedback
- Intra-undulator orbit (air coils)
- Phase shifters
- Should they be optimized one-by-one or in sets, via scan or via extremum-finding? The most time-efficient method should be preferred.
- As far as we know, Matthias is preparing a tool for fast, continuous phase shifter scans.
- There have been reports that hysteresis is an issue. Yuhui is going to gather some information.
- Undulator taper
- Could be optimized automatically, but has not been tried yet.
- We should verify if the taper settings recommended by the LCLS tool agree with reality.
- RF chirp & curvature, gun phase
- Can be tuned via optimizer, but requires manual selection of bounds and actuators so far.
- Automatic optimization based on BCM/XGM correlations is possible.
- Injector trim coil
- Is a strong tuning knob, believed to have an impact on the beam tilt (z-x or z-y correlation).
- Trajectory in pre-BC2 sections
- The orbit in the low-to-medium energy part of the machine can have significant impact on the FEL process.
- Insufficient understanding for automatic tuning.
- Laser heater (intensity, position)
- Optics (quadrupoles upstream of undulators)
Required diagnostics & tools:
- Gain curve measurement
- A fast measurement of the gain curve could help us better understand where and what to tune. We have no clear picture how far Lyuba's efforts have come.
- Online spectrometer
- An online spectrometer would also help with tuning. The quality of the spectrum might be a direct input to optimization algorithms together with the intensity.
- K values should be measured and equalized once a lasing trajectory has been found. Other labs have reported that a fast scan with a photodiode works well – why do we use slow image processing?
- GUIs with launch parameters: We'll try to make existing optimizer settings more easily accessible. For example, the adaptive orbit feedback for SASE2 could be started directly by a button on a DOOCS panel. Another button could start the optimizer with a preset for optimizing the SASE1 quads.
- Autonomous scripts: Well-working setups can then be automated further so that they can be started and stopped without additional user interaction.
- Server integration: Well-working scripts could be replaced by servers or started by a master-optimization server in a fashion similar to Florian's PSYCO.
- Gather information on hysteresis of phase shifters Unknown User (yuhui)