Collider Ring Research Articles

Recent progress and future plan for STCF collider ring lattice design

The Super Tau-Charm Facility (STCF) is a proposed dual-ring electron–positron collider in China, designed to operate at a center-of-mass energy (CME) range of 2–7[Formula: see text]GeV with symmetric beam energies. The collider aims for a luminosity exceeding [Formula: see text] at the beam energy of 2.0[Formula: see text]GeV. This work presents the preliminary lattice design for the STCF collider ring, specifically optimized for the 2.0[Formula: see text]GeV beam energy. To improve the nonlinear dynamics performance, the optimization of lattice is carried out by adjusting the strengths of sextupole and octupole magnets following the tuning of phase advances.

The new progress in injector and positron source of STCF

A proposal has been made for the construction of a new generation of high-luminosity electron-positron colliders known as the Super Tau-Charm Facility (STCF) in China. The STCF aims to achieve a luminosity exceeding [Formula: see text][Formula: see text]cm[Formula: see text][Formula: see text]s[Formula: see text] and will operate within a center-of-mass energy range of 2 to 7[Formula: see text]GeV. Given the design challenges of the STCF collider ring, swap-out injection has been proposed as an alternative method for achieving the desired luminosity. Consequently, the STCF injector will explore both off-axis injection and swap-out injection methods concurrently. This paper will detail the ongoing research progress on these two injection techniques.

Nonlinearity optimization for the lattice of SPPC collider ring

Nonlinearity optimization for the lattice of SPPC collider ring

Impedance driven collective effects in CEPC

The Circular Electron Positron Collider is a double ring lepton collider covering beam energy from 45 GeV (Z) to 180 GeV (tt-bar). Beam coupling impedance and the collective effects that are triggered by the impedance are important subjects when targeting high machine performance of an electron positron collider. A robust impedance model is required for the instabilities evaluations as well as to investigate their possible mitigations. Meanwhile, a thorough investigation on the collective effects is essential to identify the critical issues on the beam instabilities. In this paper, a detailed impedance model has been built for the collider ring and dominant impedance contributors have been identified by evaluating the effective impedances. The potential collective instabilities driven by the impedance are also discussed.

Booster free from spin resonance for future 100-km-scale circular e+e− colliders

Acceleration of polarized electron~(positron) beams in a booster synchrotron may suffer from depolarization due to crossings of many spin depolarization resonances, which could limit its applications. We have studied the spin depolarization resonance structure of a 100~km scale booster lattice of the Circular Electron Positron Collider~(CEPC). The lattice has 8 arc regions with hundreds of FODO cells, interleaved with straight sections, which leads to a high periodicity. Our analysis shows the contributions to the strength of intrinsic and imperfection spin resonances add up coherently near the super strong resonances beyond 120 GeV, but mostly cancel out and result in generally weak resonance strengths at lower beam energies. Detailed simulations confirm that beam polarization can be mostly maintained in the fast acceleration to 45.6 GeV and 80 GeV, but severe depolarization may occur at even higher energies. This study suggests the possibility of acceleration of polarized electron~(positron) beams to ultra-high beam energies without the help of Siberian snakes, and supports injecting highly polarized beams into the collider rings as an attractive solution for resonant depolarization measurements and longitudinal polarized colliding beam experiments for future 100~km scale circular e$^{+}$e$^{-}$ colliders.

Development of ceramic vacuum chamber for collider ring kicker of Circular Electron Positron Collider (CEPC)

The fast-pulsed kicker of the collider ring of Circular Electron Positron Collider (CEPC) uses a ceramic vacuum chamber to reduce eddy currents and maintain the magnetic field waveform at the beam's track. But the image charges induced by beams will accumulate on the insulating ceramic to increase the beam impedance. Eddy current shielding and beam impedance are traded off by coating a discontinuous “pattern” of TiN (titanium nitride) film on the inner wall of the ceramic vacuum chamber. Several potentially effective coating patterns are proposed. The eddy current shielding effect and the beam impedance are analyzed by simulation software. The simulation results show that coating in a ladder-shaped pattern maintains the magnetic field waveform well and helps to reduce the impedance. Properties such as electrical conductivity and SEY (secondary electron yield) of the films are improved in coating experiments and the technical feasibility of coating in a racetrack-shaped ceramic vacuum chamber is verified. Finally, the impedance of a 1200 mm-long ceramic vacuum chamber coated with ladder-shaped pattern film and the effect on the kicker magnetic field are measured.

RHIC optics and spin dynamics with snakes and rotators

The operation of RHIC collider rings in polarized proton runs includes helical snakes, which allow for preserving polarization during acceleration to store energies. The RHIC lattice also includes spin rotators, operated when nonvertical polarization or corrections to the orientation of polarization at the interaction points are required. Utilization of OPERA field maps of snakes and rotators has been systematized in the past decade, in order to assess in detail the effects of these spin devices on beam polarization, and their perturbative effects on beam optics. The method is also used in ongoing studies regarding the future Electron Ion Collider, to permit increasing average store polarization to at least 70% at 275 GeV and the acceleration of polarized helion with low polarization losses. This paper reviews various applications and outcomes of these field map methods. It is thereby also a review of studies undertaken as part of beam polarization research activities at RHIC in recent years.

Investigation of spin rotators in CEPC at the Z-pole

PurposeLongitudinal polarization is an important design aspect of the future 100 km-scale Circular Electron Position Collider (CEPC). Spin rotators are needed in the CEPC collider rings to make the beam polarization along the longitudinal direction at the interaction points (IPs). This paper focuses on the design of spin rotators for CEPC at the Z-pole (45.6 GeV).MethodsThe design of spin rotators in the CEPC at the Z-pole is based on solenoid magnets and horizontal bending magnets sections. The coupling of transverse motion introduced by solenoids is compensated with quadrupole lenses. Adjustments have been made to the layout to implement the spin rotators into the collider rings.ResultsLongitudinal polarized beam can be achieved at the IPs with the spin rotators. High degree of polarization is attainable, while the effect of spin rotators on orbital motion is acceptable. The detailed simulation results will be presented.ConclusionA solenoid-based spin rotator configuration is designed and integrated into the CEPC collider ring lattice. According to the simulation results, the polarization requirements can be satisfied.

Circular accelerator lattices with skew quadrupoles

Circular accelerator lattices are usually confined in the horizontal plane. Optics design does not rely on the orbit in the vertical direction. Here we propose a circular accelerator lattice in which the orbit moves in both horizontal and vertical directions. Having another degree of freedom, flexibility of the optics increases with less constraints of the orbit, e.g. a zero momentum compaction factor lattice without reverse bending magnets or a negative dispersion function. As a possible application of the concept, a collider ring arc of a muon collider facility is illustrated.

The mechanical design, fabrication and tests of dressed 650 MHz 2-cell superconducting cavities for CEPC

650 MHz 2-cell superconducting radio-frequency (SRF) cavities have been adopted for the collider ring of the Circular Electron Positron Collider (CEPC). By optimizing the wall thickness and geometry, the mechanical properties of the dressed cavity have been significantly improved with a focus on stress, tuning capabilities, pressure sensitivity, and Lorentz-force detuning, while microphonics and buckling were carefully monitored. Three cavities were later fabricated, post-processed and received vertical tests. The maximum unloaded quality factor (Q0) of the cavities has reached 3.2 × 1010 at 19.7 MV/m, which exceeded the design goal during operation. The favored small coefficient of Lorentz-force detuning was validated, too. Pressure sensitivity was measured and consistent with simulation prediction. Mounted with tuners, fundamental and high-order-mode (HOM) couplers, two dressed 650 MHz 2-cell cavities were finally integrated into a test cryomodule for a beam test facility. Both cavities were successfully tuned to the operating frequency of 650.000 MHz at 2.0 K. This article covers the mechanical aspects in the development and cryogenic tests of the 650 MHz 2-cell cavities.

Lattice Design of the CEPC Collider Ring for a High Luminosity Scheme

Lattice Design of the CEPC Collider Ring for a High Luminosity Scheme

A Correction Scheme for the Magnet Imperfection on the CEPC Collider Ring

A Correction Scheme for the Magnet Imperfection on the CEPC Collider Ring

CEPC Z-pole polarization design studies

In this paper, we give preliminary designs of beam polarization manipulations by inserting three different types of insertions in the Circular Electron–Positron Collider (CEPC) at center-of-mass energies of 91 GeV ([Formula: see text]-pole). With the wigglers in the collider ring, we can obtain 5% transverse polarization in 1.1 h for the precise energy measurement. To overcome depolarization effects as the beam energy rises from 10 GeV to 45.5 GeV in the booster ring, Siberian snakes based on helical magnets are adopted. Finally, for longitudinally polarized beam collisions, a schematic design of spin rotators based on solenoids in the collider ring is studied.

Development of the CEPC collider prototype magnets

A Circular Electron Positron Collider (CEPC) with a circumference of about 100 km and a beam energy up to 120 GeV is proposed to be constructed in China. Over 80% of the collider ring is covered by conventional magnets. Most dipole and quadrupole magnets are twin aperture magnets with an inter-beam separation of 350 mm. Two 1-meter-long twin aperture prototype magnets are designed and manufactured. One is a combined dipole–sextupole magnet with aluminum bus bar coils, and the other one is a twin aperture quadrupole magnet with a DT4 compensation sheet to reduce the crosstalk effect between the two apertures. The design, fabrication and magnetic measurement of two prototype magnets are described in this paper.

Siberian Snakes, Figure-8 and Spin Transparency Techniques for High Precision Experiments with Polarized Hadron Beams in Colliders

We present a review of the possibilities to conduct experiments of high efficiency in the nuclear and high energy physics with spin-polarized beams in a collider complex, configuration of which includes Siberian snakes or figure-8 collider ring. Special attention is given to the recently elicited advantageous possibility to conduct high precision experiments in a regime of the spin transparency (ST) when the design global spin tune is close to zero. In this regime, the polarization control is realized by use of spin navigators (SN), which are compact special insertions of magnets dedicated to a high flexibility spin manipulation including frequent spin flips.

NICA Booster Control and Diagnostics System

NICA (Nuclotron-based Ion Collider fAcility) is a new accelerator complex being constructed at the Joint Institute for Nuclear Research (Dubna, Russia). NICA will provide collider experiments with heavy ions at a maximum energy up to 4.5 GeV/u and polarized protons at energy up to 12.6 GeV. It will consist of injection complex, superconducting booster synchrotron, the Nuclotron, and two collider rings. This report describes structure, main features, and current status of a control system (CS) based on TANGO for the booster synchrotron.

Design and beam dynamics of the CEPC booster

The CEPC booster needs to provide electron and positron beams to the collider at different energy with required injection speed. A 10 GeV linac is adopted as the injector for CDR. Then the beam energy is accelerated to specific energy according to three modes of operation of the CEPC collider ring ([Formula: see text], [Formula: see text] and [Formula: see text]). The geometry of the booster is designed carefully in order to share the same tunnel with the collider. The design status of the booster with the CDR lattice including parameters, optics and dynamic aperture is discussed in this paper.

Detector and Physics Performance at a Muon Collider

A muon collider represents the ideal machine to reach very high center-of-mass energies and luminosities by colliding elementary particles. This is the result of the low level of beamstrahlung and synchrotron radiation compared to linear or circular electron-positron colliders. In contrast with other lepton machines, the design of a detector for a multi-TeV muon collider requires detailed knowledge of the interaction region due to the significant backgrounds created by muon beam decays in the collider ring. The physics reach can be properly evaluated only when the detector performance in such an environment is determined. In this work, the backgrounds generated by muon beams of 750 GeV are characterized and the performance of the tracking system and the calorimeter detector is illustrated. Solutions to minimize the effect of the beam-induced backgrounds are discussed and applied to obtain track and jet reconstruction performance. The μ+μ−→ Hνν̄→ bb̄ νν̄ process is fully simulated and reconstructed to demonstrate that physics measurements are possible in this harsh environment. The measurement precision for the Higgs boson coupling to bb̄ is evaluated for √s=1.5, 3, and 10 TeV and compared to other proposed machines.

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.

NICA absolute Polarimeter

The development of the absolute Polarimeter APol with an internal polarized atomic hydrogen/deuterium jet target for NICA collider is presented. It is proposed to install the polarimeter into the “warm” gap of the collider ring arc. The polarized jet will cross both accelerated beams. The jet target is based on the classical atomic beam source principle. Expected target thickness of the jet in the interaction regions is 1012 atom/cm2. APol utilizes a reaction of elastic scattering of identical nuclei (protons or deuterons). The polarization of the accelerated beams is determined by use of an actual analyzing power which is measured in turn in scattering of unpolarized accelerated beams on the polarized atomic jet. The polarization of the atomic hydrogen/deuterium jet will be measured by Breit-Rabi polarimeter placed under the collider ring into a jet catcher volume.