The injector cryomodule CM01 in the superconducting linac of the LCLS facility has suffered from a sudden onset of field emission in multiple cavities end of September 2023. The accelerating gradient of several had to be reduced from their previous nominal setpoints to stay within the administrative radiation limits. After some initial changes the level of radiation now remains constant. As of today, no clear root cause could be identified.
This workshop aims to gather experts from various related fields to address the following questions:
- Are there similarities to field emission problems at other accelerator facilities?
- Can we determine the root-cause for the field emission onset in CM01? Several theories have been discussed but none has been fully ruled out or confirmed yet (Latent particle contamination from assembly, new contamination with external particulates, hydro-carbons, cesium migration from the gun cathode, adsorbed gases from cooldown)
- Which diagnostic methods would be suitable to be applied on the cryomodule while installed in the tunnel (invasive or non-invasive)?
- What kind of simulations can be run to better understand the situation?
- Is there an optimal way to operate to cryomodule post field-emission onset? Should the amplitudes be lower or could they be higher than the current values?
- We are considering full replacement or plasma processing. What other potential avenues have been applied to recover cryomodule performance from field emission? What are the associated risks of each method?
- Even if a root-cause can not be found, are there ways to prevent something similar from happening again? What are potential mitigations for risks of a repeat if CM01 is replaced with a new cryomodule?
- Are there spatial patterns for field emission over the full machine and within cryomodules in the LCLS SC linac
