Jefferson Lab Electron Ion Collider Research Articles

Beam exchange of a circulator cooler ring with an ultrafast harmonic kicker

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.

Optimization of an Interaction Region Quadrupole Magnet for a Future Electron-Ion Collider at JLab

The Jefferson Lab Electron Ion Collider (JLEIC) is a proposed new machine for nuclear physics research. It uses the existing CEBAF accelerator as a full energy injector to deliver 3 to 11 GeV electrons into a new electron collider ring. An all new ion accelerator and collider complex will deliver up to 200 GeV protons. The machine has luminosity goals of 1034cm−2 sec−1. The whole detector region including forward detection covers about 80 meters of the JLEIC complex. The lattice file for the machine has changed to accommodate the higher energy; this change requires all the magnets in the interaction region to change. This paper will describe the requirements for both the ion and electron beam superconducting magnets around the interaction point. All the Final Focusing Quadrupole (FFQ) magnets now have preliminary designs. This paper will describe the optimization process for one of these FFQs. The optimization is performed using the optimization module of SIMULIA Opera FEA and compared with ROXIE. An analytical design tool has also been developed to estimate the peak field in the coils. The quadrupole has been optimized for peak field in the coils, and magnetic length.

Preliminary Design of the Interaction Region Beam Transport Systems for JLEIC

The Jefferson Lab Electron Ion Collider (JLEIC) is a proposed new machine for a nuclear physics research. As proposed, it will deliver between 15 and 65 GeV center of mass energy collisions between electrons and nuclei. It uses the existing CEBAF accelerator as a full energy injector to deliver 3-10 GeV electrons into a new electron collider ring. An all new ion accelerator and collider complex will deliver up to 100 GeV protons, or 40 GeV/nucleon ions. The machine will have luminosity goals of above 10 33 cm -2 sec -1 in the whole energy range. The two collider rings use a unique figure eight layout to deliver a high degree of polarization in both beams. The machine will ultimately include room for two interaction regions. The crossing angle in the primary interaction region will be 50 mrad. This paper will describe the requirements and preliminary designs for both the ion and electron beam transport systems in the most complex 32 m region around the interaction point. The beam transport system includes three separate cryostats housing over 37 superconducting magnets operating at 4.5 K. The design of these cryostats must be closely integrated with the elements of the JLEIC detector.

Preliminary Design Study of a Fast-Ramping Magnet for Preconcept Design of an Electron–Ion Collider at Jefferson Lab

The Jefferson Lab electron–ion collider is a proposed new machine for nuclear physics research. The all new ion accelerator and collider complex will consist of two collider rings with a unique figure-of-eight layout to deliver a high degree of polarization in both beams. As a part of the preconcept design for the Ion ring system, a fast ramping 3-T superferric dipole magnet was proposed utilizing a superconducting cable-in-conduit-conductor (CICC) design to wind the coils which will be built by Texas A&M University. The first mechanical model of the winding for the 3T-SF-CICC dipole was built to validate that the winding structure provides the conductor geometry required to provide the collider field homogeneity over large aperture. A rapid-cycling Booster synchrotron is required to inject 8 GeV beams to the Ion Ring. The Booster requires arc dipoles with the same field and aperture as those of the Ion Ring. Due to the design of the CICC with respect to the amount of stabilizer and the internal cooling mechanism employed, temperature rise of the coils during a quench event is much more rapid than for more conventional magnets. It is, thus, imperative that the magnet's stored energy is dissipated externally to the windings to avoid overheating the CICC and to provide adequate protection during a quench. This article presents a preliminary design study, including ac effects inside the coils and associated risks with the aim of providing guidance for the design of the full protection system for such a magnet.

An Increased Extraction Energy Booster Complex for the Jefferson Lab Electron Ion Collider

An Increased Extraction Energy Booster Complex for the Jefferson Lab Electron Ion Collider

Analysis of spin response function at beam interaction point in JLEIC

The spin response function is determined by a collider’s magnetic lattice and allows one to account for contributions of perturbing fields to spin resonance strengths. The depolarizing effect of an incoming beam depends significantly on the response function value at the interaction point (IP). We present an analytic calculation of the response function for protons and deuterons at the IP of Jefferson Lab Electron Ion Collider (JLEIC) over its whole momentum range. We find a good agreement of the analytic calculation with our numerical modeling results obtained using a spin tracking code, Zgoubi.

Impact of the Tilted Detector Solenoid on the Ion Polarization at JLEIC*This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contracts DE-AC05-06OR23177 and DE-AC02-06CH11357.

Jefferson Lab Electron Ion Collider (JLEIC) is a figure-8 collider “transparent” to the spin. This allows one to control the ion polarization using a universal 3D spin rotator based on weak solenoids. Besides the 3D spin rotator, a coherent effect on the spin is produced by a detector solenoid together with the dipole correctors and anti-solenoids compensating betatron oscillation coupling. The 4 m long detector solenoid is positioned along a straight section of the electron ring and makes a 50 mrad horizontal angle with a straight section of the ion ring. Such a large crossing angle is needed for a quick separation of the two colliding beams near the interaction point to make sufficient space for placement of interaction region magnets and to avoid parasitic collisions of shortly-spaced 476 MHz electron and ion bunches. We present a numerical analysis of the detector solenoid effect on the proton and deuteron polarizations. We demonstrate that the effect of the detector solenoid on the proton and deuteron polarizations can be compensated globally using an additional 3D rotator located anywhere in the ring.

Acceleration of polarized protons and deuterons in the ion collider ring of JLEIC

The figure-8-shaped ion collider ring of Jefferson Lab Electron-Ion Collider (JLEIC) is transparent to the spin. It allows one to preserve proton and deuteron polarizations using weak stabilizing solenoids when accelerating the beam up to 100 GeV/c. When the stabilizing solenoids are introduced into the collider’s lattice, the particle spins precess about a spin field, which consists of the field induced by the stabilizing solenoids and the zero-integer spin resonance strength. During acceleration of the beam, the induced spin field is maintained constant while the resonance strength experiences significant changes in the regions of “interference peaks”. The beam polarization depends on the field ramp rate of the arc magnets. Its component along the spin field is preserved if acceleration is adiabatic. We present the results of our theoretical analysis and numerical modeling of the spin dynamics during acceleration of protons and deuterons in the JLEIC ion collider ring. We demonstrate high stability of the deuteron polarization in figure-8 accelerators. We analyze a change in the beam polarization when crossing the transition energy.

Vlasov analysis of microbunching instability for magnetized beams

For a high-brightness electron beam with low energy and high bunch charge traversing a recirculation beamline, coherent synchrotron radiation and space charge effect may result in the microbunching instability (MBI). Both tracking simulation and Vlasov analysis for an early design of Circulator Cooler Ring for the Jefferson Lab Electron Ion Collider reveal significant MBI. It is envisioned these could be substantially suppressed by using a magnetized beam. In this work, we extend the existing Vlasov analysis, originally developed for a non-magnetized beam, to the description of transport of a magnetized beam including relevant collective effects. The new formulation will be further employed to confirm prediction of microbunching suppression for a magnetized beam transport in a recirculating machine design.

Multiple harmonic frequencies resonant cavity design and half-scale prototype measurements for a fast kicker

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

Ultrafast harmonic rf kicker design and beam dynamics analysis for an energy recovery linac based electron circulator cooler ring

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.