Summary of QM02 Measurements

[摘要] This note summarizes both the beam-based and various laboratory measurements of quadrupole magnets, units 387 and 428, used for QM02 in the LCLS Injector. These were undertaken because of a consistent discrepancy between accelerator model predictions and beam observations which seemed to indicate a weak QM02. A report 'QM02 Strength Measurement', by Welch and Wu, describes the discrepancy and beam-based measurements on unit 387. Subsequently, unit 387 was replaced by unit 428, refinements were made to analysis of the beam-based measurements were made, and additional magnetic measurements were made on unit 387 in the lab. These new results are summarized in this note. The principle results are: (1) Laboratory measurements of integrated gradient for the same magnet, or for different magnets of the same type, are all within 1% of each other at gradients of interest. These cases cover three independent types of measurements, disassembly/reassembly of the units, and extended periods of time between measurements. (2) Standardization, or lack thereof, can cause integrated gradient errors of approximately 0.2 kG, which can amount to a few percent of the strength of the magnet depending on the setting. (3) Model-independent beam-based measurements indicate the magnets are actually weaker than expected by about 2 percent, but these measurements are subject to the uncertainty of the BPMS1 location. (4) The standardization cycle is effective. (5) The stainless steel BPM vacuum chamber inside the magnets has no significant effect on the beam. The discrepancy between the accelerator model predictions and the actual orbit response is not resolved, but the evidence points away from magnetic strength errors as the source. Differences between the model locations and effective locations of BPM's is a possible culprit. This idea is explored in Section 2. Table 1 summarizes the measurement activities that were performed on the units. The dates listed correspond to the date when the relevent series of runs was completed.

[发布日期] 2010-12-03

[学科分类] 核物理和高能物理

[关键词] LINEAR ACCELERATORS;MAGNETS;QUADRUPOLES;ELECTRON BEAM INJECTION;FREE ELECTRON LASERS;LIGHT SOURCES;PERFORMANCE;BEAM MONITORS;POSITIONING;BEAM POSITION XFEL