Abstract
A reliable transverse emittance measurement for high-brightness electron beams is of utmost importance for the successful development of fourth generation light sources and for the beam transport in plasma-based accelerators. When the beam exhibits a significant energy spread, typical quadrupole scan emittance measurements may be affected depending on the beam properties and on the quadrupoles arrangement. The emittance degradation induced by chromatic effects in measurements involving magnetic lattices is evaluated analytically for different configurations. Analytical and numerical calculations compared with measurements have been used to evaluate the consequent error on the emittance value measured for single and double quadrupole schemes and for typical operating conditions at the SPARC facility.
Highlights
AND MOTIVATIONFourth generation light sources and advanced particle accelerators require the production, acceleration, and transport of high-brightness electron beams
The common technique used to measure the transverse emittance of beams not dominated by space charge forces relies on the measurements of the transverse beam size after a linear transport; the transverse beam size is measured at a given location while changing the upstream optics or it is measured in different locations while keeping the optics fixed
This paper focuses on the effect of chromatism on the emittance measurement of high-brightness beams, combining analytical formulas with ‘‘virtual’’ and ‘‘real’’ quadrupole scan measurements on typical SPARC beams in different operating conditions
Summary
Fourth generation light sources (e.g. free electron lasers) and advanced particle accelerators (e.g. laser and plasma wakefield accelerators) require the production, acceleration, and transport of high-brightness electron beams. Beams undergoing ultrahigh gradient acceleration (e.g. wakefield based acceleration) exhibit typically even higher energy spreads, as well as a beam divergence orders of magnitude higher than in conventional rf photoinjectors In both cases, the chromatic effect in the quadrupole scan measurement cannot be neglected and the resulting geometric emittance measurement can be affected by systematic errors due to the beam energy spread. Such large energy spread occurs, in some cases, with large transverse beam size at the entrance of the quadrupole In this condition, the measured emittance can be substantially different from the real one due to the emittance change induced by chromatic effects in the quadrupoles [18,19].
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