Abstract
Quarter wavelength resonator (QWR) based deflecting cavities with the capability of supporting multiple odd-harmonic modes have been developed for an ultrafast periodic kicker system in the proposed Jefferson Lab Electron Ion Collider (JLEIC, formerly MEIC). Previous work on the kicking pulse synthesis and the transverse beam dynamics tracking simulations show that a flat-top kicking pulse can be generated with minimal emittance growth during injection and circulation of the cooling electron bunches. This flat-top kicking pulse can be obtained when a DC component and 10 harmonic modes with appropriate amplitude and phase are combined together. To support 10 such harmonic modes, four QWR cavities are used with 5, 3, 1, and 1 modes, respectively. In the multiple-mode cavities, several slightly tapered segments of the inner conductor are introduced to tune the higher order deflecting modes to be harmonic, and stub tuners are used to fine tune each frequency to compensate for potential errors. In this paper, we summarize the electromagnetic design of the five-mode cavity, including the geometry optimization to get high transverse shunt impedance, the frequency tuning and sensitivity analysis, and the single loop coupler design for coupling to all of the harmonic modes. In particular we report on themore » design and fabrication of a half-scale copper prototype of this proof-of-principle five-odd-mode cavity, as well as the rf bench measurements. Lastly, we demonstrate mode superposition in this cavity experimentally, which illustrates the kicking pulse generation concept.« less
Highlights
To achieve high luminosity in the proposed JLEIC [1,2], an Energy Recovery Linac (ERL) based electron cooler is envisaged to cool the ion bunches with tunable energy and magnetized electron bunches.A relatively high electron beam current is needed for the eventual high luminosity upgrade scheme
The unloaded Q factors are lower than the simulation values for all modes, and this difference may be caused by imperfection of the copper material, joint losses and rf contact losses at the stub tuners, but the values are quite acceptable for this experiment
The cavity was designed and optimized to get high transverse impedances so the sum of the rf wall losses in all four cavities is less than 100 W for a kicking voltage of 55 Kick Voltage (kV)
Summary
To achieve high luminosity in the proposed JLEIC [1,2], an Energy Recovery Linac (ERL) based electron cooler is envisaged to cool the ion bunches (at energies of up to 100 GeV=u) with tunable energy (up to 55 MeV) and magnetized electron bunches. To reduce the technical challenges on the high current magnetized electron source, high order modes (HOM) damping in the superconducting radio frequency (SRF) ERL and high beam power at the dump, a multiturn electron circulator cooler ring (CCR) is proposed This will recirculate and reuse the low emittance electron bunches 10-30 turns in the CCR, allowing the bunch repetition rate and beam current in the source and. In simulations the flat-top waveform has excellent performance in conserving the transverse emittance of the cooling electron bunches during the recirculation Such a kicking pulse can be synthesized by 10 harmonic modes of the 47.63 MHz kicker pulse repetition frequency, by using four QWR based deflecting cavities with the harmonic mode number distribution of 5∶3∶1∶1 [5,6,7]. The cavity structure near the beam pipe must be optimized to reduce the on-axis longitudinal electric field component in order to reduce beam loading in the high current application
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