Main Quadrupole Research Articles

Modeling of random geometric errors in superconducting magnets with applications to the CERN Large Hadron Collider

Estimates of random field-shape errors induced by cable mispositioning in superconducting magnets are presented and specific applications to the Large Hadron Collider (LHC) main dipoles and quadrupoles are extensively discussed. Numerical simulations obtained with Monte Carlo methods are compared to analytic estimates and are used to interpret the experimental data for the LHC dipole and quadrupole prototypes. The proposed approach can predict the effect of magnet tolerances on geometric components of random field-shape errors, and it is a useful tool to monitor the obtained tolerances during magnet production.

Electrical quadrupole interaction in RNi nB nC (n = 1, 2) compounds as obtained from 57Fe Mössbauer spectroscopy, ( c′/a)-ratio and the occurrence of superconductivity

57Fe Mössbauer spectra of RNiBC (R=Gd, Tb, Dy, Ho, and Er) doped with 0.5 at % 57Fe show a main quadrupole doublet |ΔE Q| which is R dependent. The values of |ΔE Q| linearly depend on the parameter ( c′/a), with c′ being the distance of R-C layers between which the Ni 2-B 2 layer is sandwiched and a being the lattice parameter in the basal plane. A correlation between T c and ( c′/a) is also observed indicating that this structural parameter is important for the occurrence of superconductivity in this class of compounds.

A novel approach to increasing the reliability of accelerator magnets

When a very large particle accelerator with about 8000 electromagnets, such as the proposed Next Linear Collider (NLC), has an 85% overall availability goal, then all these magnets and their power supplies must be highly reliable and/or quickly repairable. An interdisciplinary reliability engineering approach, more commonly applied to aircraft and space vehicles, has been taken to design maximum reliability in the NLC main linac quadrupoles, while maintaining magnetic field performance and reducing cost. A specially assembled team of engineers with a variety of experiences with magnets carried out a failure mode and effects analysis (FMEA) on a standard SLAC quadrupole magnet system. This process helped them identify which components were less reliable. Then they redesigned the quadrupole to avoid all the potential problems. A prototype magnet will be made and tested to ensure that functionality has not been lost.

Construction of the new prototype of main quadrupole cold masses for the arc short straight sections of LHC

Each cold mass of the short straight sections in the eight LHC arcs will contain a 3.25 m long twin aperture quadrupole of a nominal gradient of 223 T/m. This magnet will be aligned in a 5.3 m long inertia tube together with auxiliary magnets on each end. On the quadrupole connection end either a pair of 38 cm long octupole or trim quadrupole magnets will be mounted, on the other end there will be combined sextupole-dipole correctors with a yoke length of 1.26 m. The powering of the main quadrupoles will be assured by two pairs of copper stabilized superconducting bus-bars placed inside the cold mass next to the bus-bars for the main dipole magnets. Each of the two quadrupole apertures will be connected to its quench protection diode. The construction of three prototypes has been entrusted to the CEA/Saclay laboratory, in the frame of the special French contribution to the LHC project. The first cold mass prototype has been completed and warm-measured for its multipole content at CEA. The second cold mass is presently under completion. The paper reviews the experience with the development of the quadrupole coils and cold mass construction and gives the results of the first warm magnetic measurements. An outlook for the series manufacture of the 400 are quadrupole magnets and their cold masses for the LHC machine completes the report.

Results of 3-dimensional structural FE-modeling of the coil end-regions of the LHC main dipoles

The transition region between the straight part and the ends of the coils of the LHC model and prototype dipole magnets are often identified as the origin of training quenches. In order to study how the discontinuities in the material properties of these regions affect coil pre-stress and possibly gain more insight in the quench behavior, a program was set up at CERN to analyze by 3D-FEM these particular regions. The ACCEL team, who performed a similar analysis for the main quadrupoles of the Superconducting Supercollider SSC, is entrusted with this program. In this paper we report on the results of 3D-modeling and analysis of the coil return end region, including the complete coil mass, of a 1-m single bore model magnet. This magnet represents all relevant features of the "two-in-one" LHC main dipole design concerning the winding configuration, the collar pack, the yoke, and the outer shell representing the He-vessel. The transition region between coil ends and straight section is modeled by slicing the magnet down to individual collar laminations per elementary level. The two-layer winding pack is represented with all individual conductor blocks, wedges, end spacers, and the interlayer spacer. Results will be presented for load cases with pre-stress after assembly at room temperature, after cool-down, and under operation at maximum current. Critical stress locations were identified in the transition into the pole free section of the magnet and in the bent part. Shimming of the coils, as well as impact from material choices and suitable alternatives are discussed.

Integrated design of superconducting accelerator magnets. A case study of the main quadrupole

This paper describes the software tool which has been developed for the design of the superconducting magnets for the Large Hadron Collider (LHC) at CERN. Applied methods include numerical field calculation with a reduced vector-potential formulation, the application of vector-optimization methods, and the use of genetic as well as deterministic minimization algorithms. Together with the applied concept of features , the software tool is used as an approach towards integrated design of superconducting magnets. The main quadrupole magnet for the LHC, which was designed at CEA Saclay (France) using a different approach, was chosen as an example for the integrated design process. The paper focuses on the design issues and is not a project report on the main quadrupoles under construction.

Slow beam extraction by a transverse RF field with AM and FM

Abstract A beam extraction method using a transverse rf electric field with amplitude and frequency modulation has been studied in order to develop an irradiation method which is synchronized with the breathing of a patient for high-quality charged particle therapy. The dependence of the extracted beam intensity on the voltage, the frequency band width and the center frequency of the transverse rf electric field has been investigated. The extracted beam intensity was slightly increased from that of the ordinary slow extraction method with a third order resonance. The response of the extracted beam intensity to the applied transverse rf electric field was as prompt as within 1 ms. The horizontal emittance of beams extracted by the present method was reduced by about 70% compared with that by the ordinary one due to utilizing a constant separatrix. Amplitude modulation can control the global beam spill structure. The frequency modulation reduced the effect of the current ripple of the main quadrupole magnets.

Effect of a pre-filter on the sensitivity of a highresolution quadrupole mass spectrometer

The effect of a pre-filter on the sensitivity of a high-resolution quadrupole mass spectrometer (QMS) has been experimentally studied. The high-resolution QMS uses the condition of a higher stable zone in the Mathieu stability diagram where the higher zone is defined as zone II having a center of a = 2.83 and q = 3.02 in the a-q plane. The pre-filter of a short auxiliary quadrupole was added in front of a main quadrupole and only an r.f. voltage was applied. A helium peak intensity (mass 4 at 50% peak resolution of 40) increased by a factor of two compared with that without the pre-filter, when an r.f. voltage ratio of the pre-filter to the main quadrupole was roughly 0.2. An ion orbit analysis is used to support the experimental result.

Tracing back measured magnetic field imperfections in LHC magnets by means of the inverse problem approach

After measuring the magnetic field of a model or prototype superconducting magnet for the Large Hadron Collider (LHC) an inverse field problem is formulated in order to explain the origin of the content of unwanted multipole terms. The inverse problem solving is done by means of a least-squares minimization using the Levenberg-Marquard algorithm. Although the uniqueness of the results remains uncertain, useful insights into the causes of measured field imperfections can be deduced. A model dipole magnet, a main quadrupole prototype and a combined dipole-sextupole corrector magnet are given as examples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Three-dimensional magnetic field produced by an axisymmetric iron yoke (SSC quadrupole)

A computational procedure in which separate analyses are performed for conductor and high-permeability iron yoke has been developed for calculating the 3-D magnetic field components. Whereas the field components of the isolated 3-D current array can be evaluated at all desired points through the use of a 3-D Biot-Savart law program, the authors have developed a method for calculating the supplemental field (the image field) that will arise as a result of the presence (coaxially) of a surrounding high-permeability magnetic yoke with an axially symmetric bore. The proposed technique is illustrated by its application to the SSC (Superconducting Super Collider) main quadrupole.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and fabrication of the prototype superconducting tuning quadrupole and octupole correction winding for the LHC project

CERN is preparing for the construction of the Large Hadron Collider (LHC) to be installed in the Large Electron Positron Collider (LEP) tunnel. The magnetic lattice of the LHC will consist of a ring of twin-aperture dipoles and quadrupoles, connected electrically in series. To adjust the working point of the machine, tuning quadrupoles will be installed in pairs in each regular cell, next to the main quadrupoles. Also, to correct multipolar field errors in the LHC, an octupole correction winding is required near each lattice quadrupole. A nested construction of these two magnets is foreseen. The design of a prototype tuning quadrupole and octupole corrector is described. Details of magnetic and mechanical calculations are given, including results from existing and specially developed computer codes, and model work. Further, the construction procedures are described, including the facilities and tooling developed by ACICA for this work.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Superconducting correction magnets for the HERA proton storage ring

The Hadron Electron Ring Accelerator proton ring is equipped with superconducting dipole and quadrupole magnets. The adjustment of the working point and the chromaticity correction are provided by quadrupole and sextupole correction coils mounted on the cold beam pipe inside the main dipole magnets by epoxy and a strong-glass-fiber wrapping. The orbit correction in the proton ring is made by superferric correction dipoles mounted in common cryostats with the main quadrupole and beam-position monitors. The layout of both types of correction magnets is described and experimental results on quenching behavior and field quality are presented. >

Mössbauer study of tourmalines

The samples of tourmalines from Lower Silesia (Poland), belonging to the schorl-dravite series were studied. The ratio of Fe3+/Fe2+ ion concentrations were determined. The numbers and intensities of the main electric quadrupole doublets were explained assuming the random distribution of Fe, Mg and Al ions in the triads of octahedra Y.

Tune Measurement and Control at the CERN-SPS

Two complementary techniques have been developed which allow the betatron tunes to be controlled during energy ramping of the SPS to a precision of better than ⫩0.002. By the use of these techniques the setting-up of the SPS as a collider and a fixed target machine is substantially simplified and better physics understanding has been gained. The first technique uses an electrostatic beam deflection every 60 ms. A Fast-Fourier Transformation of the beam response in a dedicated computer yields the betatron tunes with a precision better than 0.01. In the second technique the beam is continuously excited. The frequency of the excitation is measured and fed back to the beam by a Phase-Locked-Loop. This measurement is accurate to better than 0.001 but requires a reasonably well tuned machine. Tune deviations are automatically compensated by acting on the main quadrupoles through a software loop.

Very High Precision Current Regulated Power Supplies for the Fermilab Antiproton Source

These Power Supplies were designed to power the accumulator and debuncher storage rings at the Fermi National Accelerator Laboratory Antiproton Source. The accumulator and debuncher are both large acceptance 8 GeV storage rings. The accumulator ring has the most stringent requirements since it will be required to store beams for periods in excess of twenty four (24) hours. In order to ensure long term beam stability, resonances up to order eleven (11) must be avoided. Because of this stringent tuned stability requirement, the power supplies which power the three main quadrupole and the main dipole busses must be extremely stable. Thus the current regulation specification for these power supplies is 10 PPM (0.001%) including differential and common mode ripple, long term drift, and line and load regulation.

An Axisymmetric Viscous Vortex Motion and Its Acoustic Emission

Numerical simulation of head-on collision of two vortex rings has been made for various values of a translation Reynolds number from 50 to 500, and the profile of the acoustic wave emitted by the vortex collision is determined by using the computed development of the stream function and vorticity distributions. It is found for the higher Reynolds number range that there is an early stage during which the strength of each vortex is conserved, however, the strength decreases rapidly from an instant when the cores of the two vortices come into contact. The total kinetic energy decreases similarly. The enhancement of the energy dissipation is found to be related to the vortex stretching at the time of collision. The wave pressure is composed of two components, and comparison with experimental data obtained at much higher Reynolds numbers indicates reasonable agreement for the main quadrupole component.

Magnet systems for the Daresbury synchrotron radiation source

The design, production and testing of the main dipole and quadrupole magnets for a 2 GeV electron storage ring are described, with particular emphasis on the integrated field performance including the optimisation of magnet ends. In addition fast pulsed kicker and septum magnets for control of injection and extraction processes in both the storage ring and its booster synchrotron injector are treated. All magnets are now installed and operating routinely in the new Synchrotron Radiation Source at Daresbury.

The Closed Orbit Observation System of the CERN Antiproton Accumulator

The Antiproton Accumulator (AA) works at 3.5 GeV/c central orbit momentum, has 5O? m circumference, Q-values around 2 ? and a large dispersion, up to 10 m, over most of its circumference (see ref. 1 for description). Closed orbits have to be measured over the whole range of the very large momentum acceptance (6.5%) and at beam intensities as low as 5 × 109 particles (1.5 mA). Furthermore, the pick-up electrodes have to serve as clearing field electrodes and no straight section space was available for them. They have to be compatible with an UHV of 10-11 Torr and bakeable to 300°C. The AA closed orbit observation system therefore has several unusual features: a wide range of dimensions of the pick-up electrodes, adapted to beam size, up to 70 cm horizontal width; location inside the main magnets and quadrupoles; high input impedance head amplifiers, mounted directly on the vacuum chamber feedthroughs; electronic normalizers to provide the ratio of difference/sum signals; high precision for measuring orbits far from centre. Acquisition, calibration, data treatment and display are performed with the single, stand-alone, controls computer.

Synchrotron Magnets for the SNS

The design and construction of the magnets for the 800MeV proton synchrotron which forms part of the Spallation Neutron Source is described. Operating at 50Hz, the design intensity of 2.5×1013 protons per pulse imposes stringent conditions on design and hardware, and requires that maintenance philosophy should be determined well in advance. The parameters of the main ring dipoles and quadrupoles are largely dictated by the fact that they must form a suitable load for the resonant power supply, inherited from Daresbury Laboratory's NINA electron accelerator. Programmable correction quadrupoles and octupoles are required to provide ramped fields during the 480?sec-long injection period.

Fermilab Main Accelerator Quadrupole Transistorized Regulators for Improved Tune Stability

During early operation of the Fermilab Main Accelerator, tune flucutations, caused by the SCR-controlled power supplies in the quad bus, limited the beam aperature at low energies. To correct this problem, two transistorized power supplies were built in 1975 to regulate and filter the Main Ring quad magnet current during injection and beam acceleration through the rf transistion region. There is one power supply in series with each quad bus. Each supply uses 320 parallel power transistors and is rated at 300A, 120V. Since the voltage and current capabilities of the transistorized supplies are limited, the supplies are turned-off at about 25GeV. A real-time computer system initiates turn-on of the SCR-controlled power supplies and regulation takeover by the SCR-controlled supplies, at the appropriate times.