Undulator Changes Due To Temperature Excursions

[摘要] The temperature of the LCLS undulators has not been controlled during storage. The effects of the temperature excursions are documented in this note. After a number of LCLS undulators were tuned, fiducialized, and placed in storage anticipating their use, a test was made to ensure that their properties had not changed. The test revealed, however, that indeed the undulators had changed. Detailed study of this problem followed. We now believe that the gap of the undulators changes permanently when the undulators go through temperature excursions. We have tested the other possible cause, transportation, and do not see gap changes. In this note, we document how the undulators have changed since they were originally tuned. The undulators were tuned and fiducialized in the Magnetic Measurement Facility (MMF). Afterward, many of them (approximately 18) were taken to building 750 for storage during summer and fall 2007. Building 750 had no temperature control. The undulator temperatures went from 20 C, used for tuning, down to approximately 11 C during the winter. In January 2008, three of the undulators were brought back to the MMF for a check. All three undulators showed similar changes. Trajectories, phases, and most undulator properties stayed the same, but the fiducialization (beam axis position relative to tooling balls on the undulator) had changed. Further investigation showed that the undulator gap was altered in a periodic way along the magnetic axis with a net average gap change causing the fiducialization change. A new storage location in building 33 was found and future undulators were placed there. A failure in the temperature control, however, caused the undulators to get too hot. Again the gap changed, but with a different periodic pattern. This note documents the measured changes in the undulators. In particular, it shows the detailed history of undulator 39 which went through both negative and positive temperature excursions.

[发布日期] 2010-11-17

[学科分类] 核物理和高能物理

[关键词] STORAGE;TEMPERATURE CONTROL;TRAJECTORIES;TUNING;WIGGLER MAGNETS