Final Doublet Research Articles

Synchrotron radiation from final doublet magnets in CEPC MDI

The Circular Electron Positron Collider (CEPC) is a proposed Higgs factory with center-of-mass energy of 240[Formula: see text]GeV to measure the properties of Higgs boson and test the standard model accurately. Synchrotron radiation (SR) generated from the final doublet (FD) magnets in the interaction region of CEPC double ring scheme is one of the typical issues. SR photons can contribute to the heat load of the beam pipe and cause photon background to the experiments. Furthermore, the radiation dose can damage detector components. In this paper, SR generated from FD magnets is analyzed when beam is with tails and offset. SR from the dipole leakage field of the FD superconducting magnets is also analyzed and the physics limit is given to protect the detector.

Accelerator physics design in the interaction region for CEPC double ring scheme

With the discovery of the Higgs boson at around 125 GeV, a circular Higgs factory design with high luminosity [Formula: see text] is becoming more popular in the accelerator world. The CEPC project in China is one of them. Machine Detector Interface (MDI) is the key research area in electron–positron colliders, especially in CEPC; it is one of the criteria to measure the accelerator and detector design performance. Because of the limited space available in the designed tunnel, many equipment including magnets, beam diagnostic instruments, masks, vacuum pumps, and components of the detector must coexist in a very small region. In this paper, some important MDI issues will be reported for the Interaction Region (IR) design, e.g. the final doublet quadrupoles physics design parameters, beam-stay-clear region and beam pipe, synchrotron radiation power and critical energy are also calculated.

Arrested Coalescence of Viscoelastic Droplets: Ellipsoid Shape Effects and Reorientation.

The stable configurations formed by two poroelastic, ellipsoid-shaped droplets during their arrested coalescence have been investigated using micromanipulation experiments. Ellipsoidal droplets are produced by millifluidic emulsification of petrolatum into a yield stress fluid that preserves their elongated shape. The liquid meniscus between droplets can transmit stress and instigate movement of the droplets, from their initial relative position, in order to minimize doublet surface energy. The action of the liquid meniscus causes the ellipsoidal droplets to undergo rolling and reorientation events because of their unique ellipsoid shape and associated variation in the surface curvature. The final configuration of the droplets is controlled by the balance between interfacial Laplace pressure and internal elasticity, as well as a constraint force that resists complete minimization of surface energy. Geometric and surface energy calculations are used to map the possible and most likely configurations of the droplet pairs. Experimental deviations from the calculations indicate the magnitude and potential origin of the constraint force resisting full equilibration. Droplet aspect ratio and elasticity are both shown to influence the degree of reorientation and stability of the droplets at energy extrema. Higher aspect ratios drive greater reorientation and better agreement with final doublet configurations predicted by energy minimization. Lower elasticity droplets undergo secondary deformations at high aspect ratios, further broadening the space of possible morphologies.

Tuning of CLIC-Final Focus System 3 TeV Baseline Design Under Static and Dynamic Imperfections

In this paper we present the tuning study of the Compact Linear Collider - Final Focus System (CLIC-FFS) 3 TeV baseline design under static and dynamic imperfections for the first time. The motion of the FFS magnets due to ground motion and the impact of active and passive mechanisms envisaged to stabilize both e− and e+ systems are described. It is found that the Pre-isolator required for stabilization of the Final Doublet drives the performance of the collider at the final stages of the tuning process. The obtained tuning performance depending on the stabilization techniques are discussed in detail.

Probing halfβy*optics in the Accelerator Test Facility 2

A nanometer beam size at the interaction point (IP) is required for future linear colliders to achieve the desired rate of particle collisions. KEK Accelerator Test Facility 2 (ATF2), a scaled down implementation of the linear collider beam delivery system, serves for demonstrating the feasibility of the final focus system (FFS). An unprecedented low vertical beam size at the IP of about 40 nm has been already measured in ATF2 using the optics with a nominal ${\ensuremath{\beta}}_{y}^{*}$. In our study we decrease the ${\ensuremath{\beta}}_{y}^{*}$ value in order to investigate the performance of more chromatic optics and to study the limits of beam focusing at the IP. Stronger beam focusing amplifies the aberrations from the final focus imperfections which cause an increase of the beam size at the IP. Simulations show that the multipolar errors and final doublet fringe fields spoil the IP beam sizes for ultralow ${\ensuremath{\beta}}_{y}^{*}$ optics but can be mitigated either by increasing the value of the horizontal ${\ensuremath{\beta}}^{*}$ or installing a pair of octupole magnets. We report on our first experimental steps towards the ultralow ${\ensuremath{\beta}}_{y}^{*}$ in ATF2. New methods for the beam diagnostics at the IP were developed in order to precisely set the desired optics. ${\ensuremath{\beta}}_{y}^{*}$ value was half the nominal value. The beam tuning was performed and the measured beam size is compared with the simulation results.

Population transfer in a Λ-type five-level system with equally populated initial and empty final doublet states

We investigate the selective and efficient population transfer in a Λ-type five-level system with equally populated initial and empty final doublet states by time-separated chirped pump and Stokes pulses. We show that it is possible to achieve selective, efficient, and robust population transfer from either of the equally populated initial doublet states to either of the final ground doublet levels by merging stimulated Raman adiabatic passage and chirped adiabatic passage techniques. Moreover, the maximal coherent superpositions between either of the initial doublet states and either of the final doublet states, between the intermediate level and either of the final doublet states, or between the final doublet levels can be achieved by varying the chirp rates and single-photon detuning of the pump and Stokes pulses. This method may have potential applications in quantum coherent control of population dynamics in realistic atomic or molecular systems with equally populated initial and empty final manifolds.

Budgeting and control of the mechanical noise in the International Linear Collider final focus system

In this paper, we present a simplified vibration model of the silicon detector (SiD), where the final doublet (QD0) is captured inside the detector and the penultimate magnet (QF1) is inside the machine tunnel. Ground motion spectra measured at the detector hall at SLAC have been used together with a spectrum of the technical noise on the detector. The model predicts that the maximum level of rms (root mean square) vibration seen by QD0 is well below the capture range of the interaction point (IP) feedback system available in the ILC. With the addition of an active stabilization system on QD0, it is also possible to get closer to the stability requirements of the compact linear collider (CLIC). These results can have important implications for CLIC.

Design and high order optimization of the Accelerator Test Facility lattices

The Accelerator Test Facility 2 (ATF2) aims to test the novel chromaticity correction scheme which is implemented in the final focus systems of future linear colliders such as the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). The ATF2 nominal and ultralow ${\ensuremath{\beta}}^{*}$ lattices are designed to vertically focus the beam at the focal point, or usually referred to as interaction point (IP), down to 37 and 23 nm, respectively. The vertical chromaticities of the nominal and ultralow ${\ensuremath{\beta}}^{*}$ lattices are comparable to those of ILC and CLIC, respectively. When the measured multipole components of the ATF2 magnets are considered in the simulations, the evaluated spot sizes at the IP are well above the design values. In this paper we describe the analysis of the high order aberrations that allows identifying the sources of the observed beam size growth. In order to recover the design spot sizes three solutions are considered, namely final doublet replacement, octupole insertion, and optics modification. Concerning the future linear collider projects, the consequences of magnetic field errors of the focusing quadrupole magnet of the final doublet are also addressed.

Luminosity studies in a traveling waist regime in the Compact Linear Collider

The final focus system of the Compact Linear Collider (CLIC) features a crab cavity just before the final quadrupole doublet to ensure head-on collisions at the interaction point. A decrease in the expected luminosity with respect to the case without crossing angle has been recently observed in simulations for the CLIC baseline configuration. This effect is explained from the aberrations induced due to a $z$-dependent off-center horizontal orbit in the final focus sextupoles produced by the crab cavity. Three options to recover from this loss are explored. The effect of the longitudinal $E\mathrm{\text{\ensuremath{-}}}z$ correlation of the incoming beam from the linac is taken into account and its effect on the expected luminosity is evaluated.

Analysis and control of wakefields in X-band crab cavities for Compact Linear Collider

The Compact Linear Collider requires a crab cavity on each beamline prior to the interaction point to rotate the bunches before collision. The cavities are X-band travelling wave type and are located close to the final doublet of the beam delivery system. This makes the beam very sensitive to transverse momentum imparted by wakefields; hence the wakefields must be tightly controlled. Of special concerns are the orthogonal polarisation of the operating mode and the fundamental monopole mode of the crab cavity. The former mode is at the same frequency as the operating mode of a cylindrically symmetric cavity and the latter one is at a lower frequency and hence is difficult to damp using a single means. In this paper major problematic modes of the crab cavity are investigated and damping requirements for them are calculated. Possibility of meeting the required wakefield control using waveguide damping and choke damping is thoroughly investigated. As a comparison, damped-detuning is also investigated. ► Luminosity regain using crab cavities in the CLIC collider requires tight control of long range wakefields. ► Desired wakefield control is achieved by using lower order, same order and higher order mode dampers. ► Waveguide and choke dampers are shown to be useful candidates. ► Selectively shifting certain mode(s) that dominate the wakefield relaxes the damping requirements.

One-stage probe-forming systems with quadrupole lenses excited by individual power supplies

The work deals with the ion-optical characteristics of the probe-forming systems based on a quadruplet of magnetic quadrupole lenses with four power supplies. The excitation of the lenses of a final doublet of such system is determined from the stigmatic focusing conditions, and the excitations of the first two lenses (downstream the beam) are free parameters which form a parametric set of the probe-forming systems. For this parametric set, the system acceptance reduced to the envelope dimensions in the target plane is determined as a figure of merit for the optimization task. The solution of this task gives optimal excitations of the first two lenses allowing an increase in demagnifications and acceptance of the probe-forming systems with individual power supplies in comparison with a separated Russian quadruplet.

Luminosity performance studies of the compact linear collider with intra-train feedback system at the interaction point

To achieve the design luminosity at future linear colliders, control of beam stability at the sub-nanometre level at the interaction point will be necessary. Any source of beam motion which results in relative vertical offsets of the two beams at the interaction point may significantly reduce the luminosity from the nominal value. Beam-based intra-train feedback systems located in the interaction region are foreseen to correct the relative beam-beam offset and thus to steer the two beams into collision. These feedback systems must be capable of acting within the bunch train. In addition, these feedback systems might considerably help to relax the tight stability tolerances required for the final doublet magnets. For the Compact Linear Collider (CLIC), the extremely short nominal bunch spacing (0.5 ns) and very short nominal pulse duration (156 ns) make the intra-train feedback implementation technically very challenging. In this paper the conceptual design of an intra-train feedback system for the CLIC interaction point is described. Results of luminosity performance simulations are presented and discussed for different scenarios of ground motion. We also show how the intra-train feedback system can help to relax the very tight tolerances of the vertical vibration on the CLIC final doublet quadrupoles.

Practical Applications of Permanent Magnet Multipoles

Permanent magnets are superior to electromagnets in generating strong multipole magnetic fields. Their fields are sometimes stronger than those that can be generated by superconducting magnets with the same bore radius, when the number of poles are higher. Three fabricated multipoles including a quadrupole magnet for the ILC (International Linear Collider) final focus doublet, a quadrupole magnets as a spin filter for cold neutrons, and a sextupole magnet for neutron beam focusing are described.

Selective and efficient control of coherent population transfer with time-separated chirped pulses

We propose a selective, efficient, and robust way to realize control of coherent population transfer in a $\ensuremath{\Lambda}$-type four-level system with a closely spaced doublet in the final state with time-separated chirped pump pulse and Stokes pulse pair by merging stimulated Raman adiabatic passage, temporal coherent control, and chirped adiabatic passage techniques. Moreover, an arbitrary coherent superposition between the final doublet, or between the intermediate state and either of the doublets can be created. This method holds the ability to ``control with control'' and has potential applications in coherent control of chemical reactions and quantum information processing.

Strong Variable Permanent Multipole Magnets

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Three super strong permanent multipole magnets have been made: a fixed strength quadrupole, a variable quadrupole and a variable sextupole. The inner and outer diameters of the first 100 mm-length quadrupole are 14 mm and 100 mm, respectively. This fixed strength quad has an integrated gradient of 28.5 T; where the gradient at the center is more than 2.9 T/cm. The second, variable, quadrupole has an integrated strength of 38 T with 15 mm inner diameter and 230 mm length at the maximum: there are sixteen positions in its variable strength with about a 2 T even step width. The sextupole model is intended to change its strength at 25 Hz. One application of a variable quadrupole magnet is a final doublet quadrupole for an e+e- linear collider. Permanent magnet sextupoles are useful for focusing of cold neutrons, which are a very useful probe for material research. Strong octupoles for beam tail folding in the final focus beamline of a linear collider will also be possible with permanent magnets. These high order multipoles made from permanent magnets can achieve higher strengths, for a given bore radius, than superconducting ones. Design works are presented starting from brief review. </para>

Overview of the 13,000 Magnets in the International Linear Collider

The international linear collider has about 80 km of beamlines which require over 13,000 magnets for focusing and steering the beams. Approximately 18% are superconducting magnets and the rest conventional warm iron-dominated magnets with copper coils, totaling about 135 styles. Superconducting technology is primarily used for the magnets located in the linacs' RF cryomodules, but it is also required for the spin rotation solenoids, damping ring wigglers, positron source undulator and beam delivery octupoles, sextupoles and final doublet quadrupoles. A major criterion for ILC magnet design is to achieve very high in spite of the very large number of magnets. The availability goal of the ILC is 85% (or better) and the magnets have been budgeted to cause no more than 0.75% down time. Alignment and mechanical stability requirements in many areas are very challenging. In the Beam delivery system, beam positions must be maintained at sub-micron levels to collide the beams at the interaction point. The ILC has 11 styles of kicker, pulsed or septum magnets. Some kickers need rise and fall times of a few ns and will require very powerful pulsers. Strategies for dealing with the major challenges confronting the ILC magnets will be described.

New final doublets and power densities for the international linear collider small crossing angle layout

In this paper we use current and proposed final doublet magnet technologies to reoptimise the interaction region of the international linear collider and reduce the power losses. The result is a set of three new final doublet layouts with improved beam transport properties. The effect of localised power deposition and it’s reduction using tungsten liners are considered.

Improved final doublet designs for the ILC small crossing angle scheme

The International Linear Collider (ILC) baseline layout consists of two interaction regions, both with a 14mrad beam crossing angle. The main alternative layout uses a small beam crossing angle of 2mrad, and is preferred by the physics and detector communities.It is known that the outgoing beam losses in the final doublet andsubsequent extraction line are larger in the 2mrad than in the 14mrad layout. In this work, we exploitNbTi and Nb3Sn superconducting magnet technologies to redesign and optimisethe final doublet region of the 2mrad scheme, with the aim of providing satisfactory outgoing disrupted beampower losses in this region. We present three new final doublet layouts, specifically optimisedfor the 500GeV and the 1TeV machines.

Chromaticity and low-β insertions in particle colliders

Abstract Besides its energy range, the main characteristic of a particle collider is its luminosity. A very important piece of equipment to achieve high luminosities is a low-β insertion, a device which focuses the beam down to a tiny spot size. The focusing limits are not only technological, they are also associated with the aberrations of such systems. This paper deals with the chromatic aberrations. In a first part, the treatment of the focusing errors is reviewed and a formalism using symbolic computation is set up so that high-order perturbations can be evaluated, although results are limited to the second-order betatron tune shift and to its interpretation. In a second part, a completely analytical theory of the final doublet of a low-β insertion is given for a special model of flat-beam focusing.

Design of a Transport System for High Intensity Beams

A system has been designed which is calculated to be capable of transporting up to 50 mA of 3 MeV protons a distance of seventy-five feet. The beam is contained within a radius of one inch and its phase plot is optimally matched to the acceptance of the synchrotron. This phase matching is accomplished over a wide range of beam currents by varying the excitation of the final quadrupole doublet. A computer program written to calculate the dynamics of the beam is described and some of its characteristics are discussed.