| Paper | Title | Page |
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| TUPPH033 | LCLS Compressor Dipole Field Quality and Beam Measurements | 313 |
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| FELs typically use special arrangements of dipole magnets called chicanes to create an energy dependent path length needed for bunch compression. Ideally a chicane takes a beam with a linear correlation of energy and longitudinal position, and forms a compressed bunch with the same energy spread. To a very high degree the chicane should not generate residual dispersion which can convert energy spread into emittance and degrade the FEL. Linear dispersion is correctable but it is impractical to correct non-linear dispersion or non-linear focussing effects. Thus there are stringent demands on dipole field quality. The first LCLS chicane was initially found to generate substantial emittance growth. We made beam-based measurements of the net integrated magnetic field and determined that the dipole field quality was not adequate. Subsequently we modified two of the four dipoles to improve their good-field region. When reinstalled we found the chicane generated very little emittance growth. Beam-based measurement of the integrated field confirmed the improved dipole field quality. |