Abstract
An ultrafast kicker system is being developed for the energy recovery linac (ERL) based electron circulator cooler ring (CCR) in the proposed Jefferson Lab Electron Ion Collider (JLEIC, previously named MEIC). In the CCR, the injected electron bunches can be recirculated while performing ion cooling for 10--30 turns before the extraction, thus reducing the recirculation beam current in the ERL to $1/10\ensuremath{-}1/30$ ($150\text{ }\mathrm{mA}\ensuremath{-}50\text{ }\mathrm{mA}$) of the cooling beam current (up to 1.5 A). Assuming a bunch repetition rate of 476.3 MHz and a recirculating factor of 10 in the CCR, the kicker is required to operate at a pulse repetition rate of 47.63 MHz with pulse width of around 2 ns, so that only every 10th bunch in the CCR will experience a transverse kick while the rest of the bunches will not be disturbed. Such a kicker pulse can be synthesized by ten harmonic modes of the 47.63 MHz kicker pulse repetition frequency, using up to four quarter wavelength resonator (QWR) based deflecting cavities. In this paper, several methods to synthesize such a kicker waveform will be discussed and a comparison of their beam dynamics performance is made using ELEGANT. Four QWR cavities are envisaged with high transverse shunt impedance requiring less than 100 W of total rf power for a Flat-Top kick pulse. Multipole fields due to the asymmetry of this type of cavity are analyzed. The transverse emittance growth due to the sextupole component is simulated in ELEGANT. Off-axis injection and extraction issues and beam optics using a multicavity kick-drift scheme will also be discussed.
Highlights
Cooling of ion beams will be a critical technology in delivering high luminosities over a broad center of mass (CM) energy range in the proposed JLEIC [1,2]
The present JLEIC design envisages an energy recovery linac (ERL)-based high-energy magnetized and bunched electron beam cooler in the collider ion ring to cool the ions at energies of up to 100 GeV=u, as shown in Fig. 1, with the option of adding a recirculation ring as a future upgrade
The bunch repetition rate and the beam current in the ERL can be reduced by a factor of 10–30 compared to the beam in the circulator ring, which greatly eases the technical challenges of the high current magnetized electron source, high order modes damping in the ERL and high power at the beam dump [3,4,5]
Summary
Cooling of ion beams will be a critical technology in delivering high luminosities over a broad center of mass (CM) energy range in the proposed JLEIC [1,2]. The present JLEIC design envisages an energy recovery linac (ERL)-based high-energy (up to 55 MeV) magnetized and bunched electron beam cooler in the collider ion ring to cool the ions at energies of up to 100 GeV=u, as shown in Fig. 1 (solid black), with the option of adding a recirculation ring (dash green) as a future upgrade. We will discuss an efficient rf-based kicker concept proposed to produce the pulse using harmonic rf cavities These cavities will simultaneously resonate at multiple harmonic frequencies and be excited with appropriate amplitudes and phases that correspond to the Fourier components of a periodic narrow pulse. The frequencies, phases, and relative amplitudes of each harmonic must be controlled precisely to maintain the pulse-to-pulse stability during the injection, recirculation and extraction of all bunches in the CCR
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