Abstract
We examine the use of sextupole magnets to correct nonlinearities in the longitudinal phase space transformation of a relativistic beam of charged particles in a dispersionless translating section, or dogleg. Through heuristic analytical arguments and examples derived from recent experimental efforts, augmented by simulations using the particle tracking codes PARMELA and ELEGANT, sextupole corrections are found to be effective in optimizing the use of such structures for beam compression or for shaping the current profile of the beam, by manipulation of the second-order longitudinal dispersion. Recent experimental evidence of the use of sextupoles to manipulate second-order horizontal and longitudinal dispersion of the beam is presented. The theoretical and experimental results indicate that these manipulations can be used to create an electron bunch with a current profile having a long ramp followed by a sharp cutoff, which is optimal for driving large-amplitude wake fields in a plasma wake field accelerator.
Highlights
Several experiments [1,2,3,4] in the field of beam physics have recently been proposed that require, or may benefit from, the successful transport of bunches of charged particles at large energy spread through a dispersionless translating section, or dogleg
This device, consisting of two consecutive bend magnets of opposite sense separated by dispersion-matching focusing optics, is commonly used in linear accelerator systems to translate the beam axis transversely, and it may be used as a tool to compress or shape the current profile of a relativistic electron bunch
Accelerator Center (SLAC) have been considered for the same purpose, namely, the creation of a ramped current profile [4]. This type of profile is of considerable interest as a driver for the plasma wake field accelerator (PWFA), as it allows for a high transformer ratio
Summary
Several experiments [1,2,3,4] in the field of beam physics have recently been proposed that require, or may benefit from, the successful transport (with or without compression) of bunches of charged particles at large energy spread through a dispersionless translating section, or dogleg This device, consisting of two consecutive bend magnets of opposite sense separated by dispersion-matching focusing optics, is commonly used in linear accelerator systems to translate the beam axis transversely, and it may be used as a tool to compress or shape the current profile of a relativistic electron bunch. In. Appendix D, we discuss similar calculations for the currently ongoing second phase of the VISA experiment, which indicate that these second-order effects can be minimized using sextupole correction, in order to transport a beam though the dogleg section while preserving a strong linear momentum-time correlation (chirp).
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