Quadrupole Triplet Research Articles

Mechanical Design Studies of the MQXF Long Model Quadrupole for the HiLumi LHC

The Large Hadron Collider Luminosity upgrade (HiLumi) program requires new low-β triplet quadrupole magnets, called MQXF, in the interaction region to increase the LHC peak and integrated luminosity. The MQXF magnets, designed and fabricated in collaboration between CERN and the U.S. LARP, will all have the same cross section. The MQXF long model, referred as MQXFA, is a quadrupole using the Nb3Sn superconducting technology with 150 mm aperture and a 4.2 m magnetic length and is the first long prototype of the final MQXF design. The MQXFA magnet is based on the previous LARP HQ and MQXFS designs. In this paper, we present the baseline design of the MQXFA structure with detailed three-dimensional (3-D) numerical analysis. A detailed tolerance analysis of the baseline case has been performed by using a 3-D finite element model, which allows fast computation of structures modeled with actual tolerances. Tolerance sensitivity of each component is discussed to verify the actual tolerances to be achieved by vendors. Tolerance stack-up analysis is presented in the end of this paper.

The new confocal heavy ion microprobe beamline at ANSTO: The first microprobe resolution tests and applications for elemental imaging and analysis

The Centre for Accelerator Science facility at ANSTO has been expanded with the new NEC 6MV “SIRIUS” accelerator system in 2015. In this paper we present a detailed description of the new nuclear microprobe–Confocal Heavy Ion Micro-Probe (CHIMP) together with results of the microprobe resolution testing and the elemental analysis performed on typical samples of mineral ore deposits and hyper-accumulating plants regularly measured at ANSTO.The CHIMP focusing and scanning systems are based on the OM-150 Oxford quadrupole triplet and the OM-26 separated scan-coil doublet configurations. A maximum ion rigidity of 38.9amu-MeV was determined for the following nuclear microprobe configuration: the distance from object aperture to collimating slits of 5890mm, the working distance of 165mm and the lens bore diameter of 11mm. The overall distance from the object to the image plane is 7138mm.The CHIMP beamline has been tested with the 3MeV H+ and 6MeV He2+ ion beams. The settings of the object and collimating apertures have been optimized using the WinTRAX simulation code for calculation of the optimum acceptance settings in order to obtain the highest possible ion current for beam spot sizes of 1μm and 5μm. For optimized aperture settings of the CHIMP the beam brightness was measured to be ∼0.9pAμm−2mrad−2 for 3MeV H+ ions, while the brightness of ∼0.4pAμm−2mrad−2 was measured for 6MeV He2+ ions. The smallest beam sizes were achieved using a microbeam with reduced particle rate of 1000Hz passing through the object slit apertures several micrometers wide. Under these conditions a spatial resolution of ∼0.6μm×1.5μm for 3MeV H+ and ∼1.8μm×1.8μm for 6MeV He2+ microbeams in horizontal (and vertical) dimension has been achieved. The beam sizes were verified using STIM imaging on 2000 and 1000mesh Cu electron microscope grids.

Conductor Specification and Validation for High-Luminosity LHC Quadrupole Magnets

Author(s): Cooley, LD; Ghosh, AK; Dietderich, DR; Pong, I | Abstract: The high-luminosity upgrade of the large hadron collider (HL-LHC) at CERN will replace the main ring inner triplet quadrupoles, identified by the acronym MQXF, adjacent to the main ring intersection regions. For the past decade, the U.S. LHC Accelerator RaD Program, LARP, has been evaluating conductors for the MQXFA prototypes, which are the outer magnets of the triplet. Recently, the requirements for MQXF magnets and cables have been published in [P. Ferracin et al., IEEE Trans. Appl. Supercond., vol. 26, no. 4, Jun. 2016, Art. no. 4000207], along with the final specification for Ti-alloyed Nb3Sn conductor determined jointly by CERN and LARP. This paper describes the rationale beneath the 0.85-mm-diameter strand's chief parameters, which are 108 or more subelements, a copper fraction not less than 52.4%, strand critical current at 4.22 K not less than 631 A at 12 T and 331 A at 15 T, and residual resistance ratio of not less than 150. This paper also compares the performance for ∼100 km production lots of the five most recent LARP conductors to the first 163 km of strand made according to theHL-LHCspecification.Two factors emerge as significant for optimizing performance and minimizing risk: a modest increase of the subelement diameter from 50 to 55 μm, and a Nb:Sn molar ratio of 3.6 instead of 3.4. The statistics acquired so far give confidence that the present conductor can balance competing demands in production for the HL-LHC project.

Rotating system for four-dimensional transverse rms-emittance measurements

Knowledge of the transverse four-dimensional beam rms-parameters is essential for applications that involve lattice elements that couple the two transverse degrees of freedom (planes). Of special interest is the removal of inter-plane correlations to reduce the projected emittances. A dedicated ROtating System for Emittance measurements (ROSE) has been proposed, developed, and successfully commissioned to fully determine the four-dimensional beam matrix. This device has been used at the High Charge injector (HLI) at GSI using a beam line which is composed of a skew quadrupole triplet, a normal quadrupole doublet, and ROSE. Mathematical algorithms, measurements, and results for ion beams of 83Kr13+ at 1.4 MeV/u are reported in this paper.

Achromatic beam transport of High Current Injector

The high current injector (HCI) provides intense ion beams of high charge state using a high temperature superconducting ECR ion source. The ion beam is accelerated upto a final energy of 1.8 MeV/u due to an electrostatic potential, a radio frequency quadrupole (RFQ) and a drift tube linac (DTL). The ion beam has to be transported to superconducting LINAC which is around 50 m away from DTL. This section is termed as high energy beam transport section (HEBT) and is used to match the beam both in transverse and longitudinal phase space to the entrance of LINAC. The HEBT section is made up of four 90 deg. achromatic bends and interconnecting magnetic quadrupole triplets. Two RF bunchers have been used for longitudinal phase matching to the LINAC. The ion optical design of HEBT section has been simulated using different beam dynamics codes like TRACEWIN, GICOSY and TRACE 3D. The field computation code OPERA 3D has been utilized for hardware design of all the magnets. All the dipole and quadrupole magnets have been field mapped and their test results such as edge angles measurements, homogeneity and harmonic analysis etc. are reported. The whole design of HEBT section has been performed such that the most of the beam optical components share same hardware design and there is ample space for beam diagnostics as per geometry of the building. Many combination of achromatic bends have been simulated to transport the beam in HEBT section but finally the four 90 deg. achromatic bend configuration is found to be the best satisfying all the geometrical constraints with simplified beam tuning process in real time.

The magnetic behaviour of the LHC at 6.5 TeV

After two years of shutdown, the Large Hadron Collider (LHC) operated in 2015 at an energy of 6.5 TeV. In this paper, we give the first outlook of the behavior of the LHC magnets operating at this field level, corresponding to 8-T peak field in the main dipoles. The main magnetic features are reconstructed through the beam measurements, mainly the tune (quadrupolar components) and the chromaticity (sextupolar components). The decay and snapback at injection and the start of the ramp are expected to increase by 50% due to the higher operational current. The behavior at high field will be affected by the saturation components, which were barely visible in one magnet family in the 4-TeV runs and totally invisible in the rest. Although the initial plan aims at a rather conservative value of β*, during the squeeze, the triplet and matching section quadrupole will become important. Beam measurements will provide interesting information about the magnetic behavior of these quadrupoles; in particular, through beta beating, we will estimate the absolute precision of the knowledge of the quadrupole strength. The statistics of the beam measurements will be rather limited in the first stages of commissioning, but should already reveal the main features of the 6.5-TeV operation.

Design of the large hadron electron collider interaction region

The large hadron electron collider (LHeC) is a proposed upgrade of the Large Hadron Collider (LHC) within the high luminosity LHC (HL-LHC) project, to provide electron-nucleon collisions and explore a new regime of energy and luminosity for deep inelastic scattering. The design of an interaction region for any collider is always a challenging task given that the beams are brought into crossing with the smallest beam sizes in a region where there are tight detector constraints. In this case integrating the LHeC into the existing HL-LHC lattice, to allow simultaneous proton-proton and electron-proton collisions, increases the difficulty of the task. A nominal design was presented in the the LHeC conceptual design report in 2012 featuring an optical configuration that focuses one of the proton beams of the LHC to ${\ensuremath{\beta}}^{*}=10\text{ }\text{ }\mathrm{cm}$ in the LHeC interaction point to reach the desired luminosity of $L={10}^{33}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. This value is achieved with the aid of a new inner triplet of quadrupoles at a distance ${L}^{*}=10\text{ }\text{ }\mathrm{m}$ from the interaction point. However the chromatic beta beating was found intolerable regarding machine protection issues. An advanced chromatic correction scheme was required. This paper explores the feasibility of the extension of a novel optical technique called the achromatic telescopic squeezing scheme and the flexibility of the interaction region design, in order to find the optimal solution that would produce the highest luminosity while controlling the chromaticity, minimizing the synchrotron radiation power and maintaining the dynamic aperture required for stability.

Electron beam final focus system for Thomson scattering at ELBE

The design of an electron beam final focus system (FFS) aiming for high-flux laser-Thomson backscattering X-ray sources at ELBE is presented. A telescope system consisting of four permanent magnet based quadrupoles was found to have significantly less chromatic aberrations than a quadrupole doublet or triplet as commonly used. Focusing properties like the position of the focal plane and the spot size are retained for electron beam energies between 20 and 30MeV by adjusting the position of the quadrupoles individually on a motorized stage. The desired ultra-short electron bunches require an increased relative energy spread up to a few percent and, thus, second order chromatic effects must be taken into account. We also present the design and test results of the permanent magnet quadrupoles. Adjustable shunts allow for correction of the field strength and compensation of deviations in the permanent magnet material.For a beam emittance of 13mmmrad, we predict focal spot sizes of about 40μm (rms) and divergences of about 10mrad using the FFS.

IH-DTL design with KONUS beam dynamics for KHIMA project

The Kombinierte Null Grad Struktur (KONUS) beam dynamics design of the interdigit H-mode drift tube linac (IH-DTL) for the Korea Heavy Ion Medical Accelerator (KHIMA) project is presented. We performed a KONUS beam dynamics simulation for a carbon beam (12C4+) with the LORASR code. The 12C4+ beam was accelerated from an input energy of 0.4MeV/u to an output energy of 7MeV/u by the IH-DTL operated at 200MHz. The optimization aims were to increase the transmission efficiency and to minimize the beam emittance growth, beam loss, and project costs. The buncher with two gaps and two quadrupole doublets were placed between the RFQ and the IH-DTL. The whole IH-DTL consists of two tanks, 56 acceleration gaps, and four quadrupole triplets. It achieves a transmission efficiency of 100%. The total length from the exit of the RFQ to the exit of the IH-DTL is approximately 507.7cm.

Beam Heat Loads to Superconducting Quadrupoles for BigRIPS In-Flight Separator at RIKEN

The BigRIPS in-flight fragment separator in the RIKEN Radioactive Isotope Beam Factory (RIBF) project was commissioned in 2007 and has been operated for six years. The RIBF accelerator complex has provided a wide range of heavy ion beams from deuteron to uranium with the energy of 250-345 MeV/nucleon. More than 70 experiments of unstable nuclei have been performed using the RI beams produced by the BigRIPS fragment separator. The production target of the RI beams is in close proximity to the first superconducting triplet quadrupoles (STQs) in the BigRIPS fragment separator, so that the STQ is exposed to the high radiation, which causes “beam heat loads” to the cryogenic system. The STQ consists of three air-core NbTi coils with the maximum field gradients of 24 T/m, assembled in the liquid-helium bath cryostat with the warm bore radius of 90 mm. This paper presents measurements of the radiation heat loads to the STQ cryostat for a number of experienced heavy ion beams from oxygen to uranium with the beam power of 1-7 kW. Corresponding radiation transport calculations are presented, and radiation doses and damages to the STQ system are also discussed.

Virtual charge state separator as an advanced tool coupling measurements and simulations

A new Low Energy Beam Transport (LEBT) for multicharge uranium beam will be built at GSI High Current Injector (HSI). All uranium charge states coming from the new ion source will be injected into GSI heavy ion high current HSI-RFQ, but only design ions U 4+ will be accelerated to the final RFQ energy. A detailed knowledge about injected beam- current and -emittance for pure design U 4+ ions is necessary for a proper beam line design commissioning and operation, while the measurements are possible only for a full beam including all charge states. Detailed measurements of beam current and emittance are performed behind the first quadrupole triplet at the beam line. A dedicated algorithm, based on combination of measurements and results of an advanced beam dynamics simulations, provides for an extraction of beam- current and -emittance for only U 4+ component of a beam. The obtained results and final beam dynamics design for the new straight beam line are presented.

Studying heavy-ion collisions with coverage near zero degrees using FAUST–QTS

Heavy-ion collisions around the Fermi energy provide a rich environment for investigating reaction dynamics and provide an opportunity to explore the transition from quasi-fission to multi-fragmentation. A new detection system, FAUST–QTS, has been commissioned at Texas A&M University in order to investigate the reaction dynamics in this transitional energy regime. FAUST–QTS is constructed through the coupling of the FAUST array to a large bore quadrupole triplet spectrometer, and designed to detect heavy fragments near the beam axis coincident with lighter particles.

Superconducting magnet system of in-flight separator for a heavy ion accelerator planned in Korea

An in-flight fragment separator, which aims to produce and study rare isotopes, consists of superferric quadrupole triplets and <TEX>$30^{\circ}$</TEX> dipole magnets to focus and bend the beams for achromatic focusing and momentum dispersion, respectively. The separator is divided into pre and main stages, and we plan to use superconducting magnets employing high-Tc superconductor (HTS) coils in the pre-separator area, where radiation heating is high. The HTS coils will be cooled by cold He gas in 20-50 K, and in the other area, superferric magnets using low-temperature superconductor (LTS) will be used at 4 K. A few LTS coils were wound and successfully tested in a LHe dewar, and the design of cryostat has been optimized. Development of the HTS coils is ongoing in collaboration with a group at KERI. An HTS coil of racetrack shape was wound and tested in a <TEX>$LN_2$</TEX> bath and in a dewar with cryocooler. No degradation on critical current due to coil winding was found.

Characterization of laser-driven single and double electron bunches with a permanent magnet quadrupole triplet and pepper-pot mask

Electron beams from laser-plasma wakefield accelerators have low transverse emittance, comparable to those from conventional radio frequency accelerators, which highlights their potential for applications, many of which will require the use of quadrupole magnets for optimal electron beam transport. We report on characterizing electron bunches where double bunches are observed under certain conditions. In particular, we present pepper-pot measurements of the transverse emittance of 120–200 MeV laser wakefield electron bunches after propagation through a triplet of permanent quadrupole magnets. It is shown that the normalized emittance at source can be as low as 1 π mm mrad (resolution limited), growing by about five times after propagation through the quadrupoles due to beam energy spread. The inherent energy-dependence of the magnets also enables detection of double electron bunches that could otherwise remain unresolved, providing insight into the self-injection of multiple bunches. The combination of quadrupoles and pepper-pot, in addition, acts as a diagnostic for the alignment of the magnetic triplet.

Progress on the Development of Cryostat for Quadrupole Triplet Magnet

The project involving the development of a heavy ion accelerator facility to produce rare isotope beams is underway in Korea. The superconducting magnet should be designed to accelerate various ions for the magnetic bending limit up to 400 MeV. The cryostat for this magnet employs an innovative design primarily driven by the requirement of user-friendliness and reliability. Also, several ancillary requirements such as background field, space restriction due to the beam line, and cryostat structure need technical attentions. The present paper describes the status of the development of the cryostat for quadrupole triplet magnet in the in-flight fragmentation separator. The concept of cryogenic design is reported, and the amount of cryogenic load is estimated by relevant thermal analysis. The structure of the cryostat to endure the heavy iron yoke including three quadrupole magnets is presented. In addition, the detail cryogenic cooling by cryocoolers and the support link for the superconducting magnet are discussed.

A First Baseline for the Magnets in the High Luminosity LHC Insertion Regions

The High Luminosity LHC (HL-LHC) project aims at accumulating 3000 fb-1 in the years 2023-2035, i.e., ten times more w.r.t. the nominal LHC performance expected for 2010-2021. One key element to reach this challenging performance is a new insertion region to reduce the beam size in the interaction point by approximately a factor two. This requires larger aperture magnets in the region spanning from the interaction point to the matching section quadrupoles. This aperture has been fixed to 150 mm for the inner triplet quadrupoles in 2012. In this paper, we give a first baseline of the interaction region. We discuss the main motivations that lead us to choose the technology, the combination of fields/gradients and lengths, the apertures, the quantity of superconductor, and the operational margin. Key elements are also the constraints given by the energy deposition in terms of heat load and radiation damage; we present the main features related to shielding and heat removal.

Fluorescence time-lapse imaging of single cells targeted with a focused scanning charged-particle microbeam

Charged particle microbeams provide unique features to study targeted and non-targeted radiation response and have recently emerged as a powerful tool to investigate radiation-induced DNA damage and repair. We have developed a charged particle microbeam delivering protons and alpha particles in the MeV energy range equipped with online time-lapse imaging capabilities. The beam is focused to a sub-micrometer beam spot under vacuum by means of a triplet of magnetic quadrupoles and extracted in air through a 200nm Si3N4 window. The end-station is equipped with an automated fluorescence microscope used for single cell targeting and online time-lapse imaging. Cells are kept in their medium during the irradiation procedure and the sample temperature is regulated to 37°C. An overall targeting accuracy of 2.0±0.7μm has been measured by tracking the re-localization of the XRCC1 protein. First measurements of this re-localization shows the ability of our system to follow online the radiation-induced re-localization of proteins in the first minutes after irradiation.

Research and development of focused proton microbeam irradiation system, SPICE for radio-biological studies.

There is continuing interest for the use of microbeam irradiation systems designed to deliver a defined number of charged particles on a single cell with a resolution of a few micrometers. Irradiation of an exact number of charged particles on a single cell means that the limitations of the Poisson distribution of the number of charged particles can be overcome. Moreover, microbeams are particularly useful for the field of radiation-induced non-targeted effects, so-called bystander effects that are considered to be one of the major effects in the low-dose region. Thus, microbeam technique is one of the powerful tools for investigating studies related to radiation effect and risk of low dose in space radiation for astronauts and cosmonauts.Our microbeam irradiation system, the Single-Particle Irradiation system to CEll (SPICE) provides a 3.4 MeV proton microbeam focused with a quadrupole magnetic lens on an upward vertical beam line. SPICE was severely damaged by the Tohoku-oki Earthquake on 11 March 2011, and was out of operation for about a year and a half. We have successfully reconstructed the facility, and it is now operational with system refinements. At present, SPICE is the only proton microbeam facility in Japan at which a single-ion single-cell irradiation can be performed on mammalian cells with stability and high throughput using an upward vertical beam of below 2-μm diameter, focused with a magnetic quadrupole triplet lens [ 1]. A variety of irradiation modes have been established for radiation-induced bystander effects, cytoplasm irradiation etc. An example of cells targeted with a multi-position targeting mode is shown in Fig. 1, which cells were targeted with five different positions in the nucleus with 50 protons per position. SPICE has been administrated as a ‘Joint-use facility for Collaborative Research’, and thus researchers outside NIRS can apply for beam time of SPICE after their research proposals are approved.Fig. 1.(A) Nuclei of HCT116 cells were targeted with five different positions (3-µm apart), and 50 protons were delivered to each position. (B) Cells were incubated for 1 h and then fixed for immunostaining against γ-H2AX.

Radioactive ion beam transportation for the fundamental symmetry study with laser-trapped atoms

The search for the violation of the fundamental symmetry in a radioactive atom is the promising candidate for precision tests of the standard model and its possible extensions. The subtle signal arising from the symmetry violation is enhanced in heavy atoms, such as a francium (Fr). To realize high precision measurements, a large amount of radioactive isotopes is required. The Fr is produced via a nuclear fusion reaction using a melted gold target with a (18)O primary beam at Cyclotron and Radioisotope Center, Tohoku University. The maximum extraction efficiency of the Fr ion was achieved at approximately 35%. The beam line consists of an electrostatic deflector, three electrostatic quadrupole triplets to the measurement area at 10 m away from the reaction point, and several beam diagnosis systems. We optimized parameters of the beam line.

Extraction of 3D field maps of magnetic multipoles from 2D surface measurements with applications to the optics calculations of the large-acceptance superconducting fragment separator BigRIPS

The fringing fields of magnets with large apertures and short lengths greatly affect ion-optical calculations. In particular, for a high magnetic field where the iron core becomes saturated, the effective lengths and shapes of the field distribution must be considered because they change with the excitation current. Precise measurement of the three-dimensional magnetic fields and the correct application of parameters in the ion-optical calculations are necessary. First we present a practical numerical method of extracting full 3D magnetic field maps of magnetic multipoles from 2D field measurements of the surface of a cylinder. Using this novel method, we extracted the distributions along the beam axis for the coefficient of the first-order quadrupole component, which is the leading term of the quadrupole components in the multipole expansion of magnetic fields and proportional to the distance from the axis. Higher order components of the 3D magnetic field can be extracted from the leading term via recursion relations. The measurements were done for many excitation current values for the large-aperture superconducting triplet quadrupole magnets (STQs) in the BigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory. These distributions were parameterized using the Enge functions to fit the fringe field shapes at all excitation current values, so that unmeasured values are interpolated. The extracted distributions depend only on the position along the beam axis, and thus the measured three-dimensional field can easily be parameterized for ion-optical calculations. We implemented these parameters in the ion-optical calculation code COSY INFINITY and realized a first-order calculation that incorporates the effect of large and varying fringe fields more accurately. We applied the calculation to determine the excitation current settings of the STQs to realize various optics modes of BigRIPS and the effectiveness of this approach has been demonstrated.