Abstract
In this paper, we describe a harmonic kicker system used in the beam exchange scheme for the circulator cooling ring (CCR) of the Jefferson Lab Electron-Ion Collider. By delivering an ultrafast deflecting kick, a kicker directs electron bunches selectively in/out of the CCR without degrading the beam dynamics of the CCR optimized for ion-beam cooling. We will discuss the design principle of the kicker system and demonstrate its performance with various numerical simulations. In particular, the degrading effects of realistic harmonic kicks on the beam dynamics, such as 3D kick field profiles interacting with the magnetized beam, are studied in detail with a scheme that keeps the cooling efficiency within allowable limits.
Highlights
A proposal [1] for the Jefferson Laboratory Electron-Ion Collider (JLEIC) includes the circulator cooling ring (CCR), which can dramatically increase luminosity of the electron-ion collision at a 45 GeV center-of-mass energy by cooling the ion beam in a storage ring at an energy of up to 100 GeV=nucleon
The cooling is done by passing the ion beam through a series of cooling solenoid channels—located in an overlapping segment of the CCR and the ion storage ring—along with a comoving electron beam [see Fig. 1(a)], whose beam parameters are dictated mostly by the ion beam parameters and listed in Table I [2]
We describe design of a harmonic kicker system and demonstrate by numerical simulations that the optimized beam dynamics of the CCR for the maximum cooling efficiency can be maintained after a harmonic kicker system is implemented
Summary
A proposal [1] for the Jefferson Laboratory Electron-Ion Collider (JLEIC) includes the circulator cooling ring (CCR), which can dramatically increase luminosity of the electron-ion collision at a 45 GeV center-of-mass energy by cooling the ion beam in a storage ring at an energy of up to 100 GeV=nucleon. [11], a linear combination of ten harmonic modes, distributed over three different cavities, was designed as a kick profile, the idea of using two kickers, IK and EK, with an intervening betatron phase advance of π to cancel out the residual fields of the kick for the recirculating bunches was conceived, and pre/post kickers (PRK/POKs) were introduced to flatten the rf curvature of harmonic kick on the exchanged bunches, preventing longitudinal profiles of angular distribution from bending into a “banana” shape These ideas were demonstrated by the numerical simulation studies using the particle tracking code ELEGANT [13] based on a simple model of the kick fields, where the only nontrivial component of the kick is in the kick direction with the spatial profile being transversely uniform and longitudinally δ functionlike or “impulsive”, i.e., F⃗ L 1⁄4 eVkðtÞδðzÞx (F⃗ L is the Lorentz force as a kick acting on an electron, e is an electron charge, Vk is a kick voltage, xis the kick direction—regardless of any physical direction and might be vertical—and z is a longitudinal coordinate with the origin at the cavity center). In the ELEGANT simulation, the extended kick profile is modeled as a series of impulsive kicks over the effective field range and the resulting Larmor emittance increase is shown to be smaller than 19 mm mrad, the tolerance limit for the efficient cooling
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