Principles developed for the construction of the high performance, low-cost superconducting LHC corrector magnets

The Large Hadron Collider (LHC) needs more than 6000 superconducting corrector magnets. These must be sufficiently powerful, have enough margin, be compact and of low cost. The development of the 11 types of magnets was spread over several years and included the magnetic and mechanical design as well as prototype building and testing. It gradually led to the systematic application of a number of interesting construction principles that allow to realize the above mentioned goals. The paper describes the techniques developed and presently used in practically all the LHC corrector magnets ranging from dipoles to dodecapoles.     

High Field Superconducting Solenoids Via High Temperature Superconductors

High-field superconducting solenoids have proven themselves to be of great value to scientific research in a number of fields, including chemistry, physics and biology. Present-day magnets take advantage of the high-field properties of Nb₃Sn, but the high-field limits of this conductor are nearly reached and so a new conductor and magnet technology is necessary for superconducting magnets beyond 25 T. Twenty years after the initial discovery of superconductivity at high temperatures in complex oxides, a number of high temperature superconductor (HTS) based conductors are available in sufficient lengths to develop high-field superconducting magnets. In this paper, present day HTS conductor and magnet technologies are discussed. HTS conductors have demonstrated the ability to carry very large critical current densities at magnetic fields of 45 T, and two insert coil demonstrations have surpassed the 25 T barrier. There are, however, many challenges to the implementation of HTS conductors in high-field magnets, including coil manufacturing, electromechanical behavior and quench protection. These issues are discussed and a view to the future is provided.     

Design of a linear bulk superconductor magnet synchronous motor for electromagnetic aircraft launch systems

High-temperature superconducting (HTS) material in bulk form is used to design a linear synchronous motor for an electromagnetic aircraft launch system. The motor is designed without an iron core. Stator coils are placed in the air while the permanent magnets used in conventional design of linear permanent magnet synchronous motors are replaced by the HTS bulk magnets. The physical, operational, and equivalent circuit parameters of the linear motor with HTS bulk magnets are compared with those of a linear permanent magnet synchronous motor and linear induction motor designed for the same application. Results show that utilizing superconducting magnets is only superior at temperatures below 40 K.     

On the optimal design of gas-cooled Peltier current leads

We perform the optimal design of gas-cooled Peltier current leads (PCLs), such that their resulting heat leaking into superconducting magnets can be minimized. Superior to previous investigations, the effect of gas cooling on both the Cu lead and the thermoelectric element in a PCL is taken into consideration. Analytical temperature distribution is derived as well as the concerned heat leaking into superconducting magnets. Numerically iterative calculations are, therefore, avoided. Moreover, temperature-entropy diagrams are constructed to distinguish conventional all-Cu leads from PCLs with and without gas cooling. Both the heat leak and the input power of current leads can be easily identified from the areas subtended by the isotherms on the simple two-dimensional temperature-entropy plane.     

Superconducting magnets for the LHC main lattice

The main lattice of the Large Hadron Collider (LHC) employs about 1600 main magnets and more than 4000 corrector magnets. All superconducting and working in pressurized superfluid helium bath, these impressive line of magnets fills more than 20 km of the underground tunnel. With almost 70 main dipoles already delivered and 10 main quadrupoles almost completed, we passed the 5% of the production and now all manufacturers have fully entered into series production. In this paper the most critical issues encountered in the ramping up in such a real large scale fabrication is addressed; uniformity of the coil size and of prestress, special welding technique, tolerances on curvature (dipoles) or straightness (quadrupoles) and of the cold mass extremities, harmonic content and, most important, the integrated field uniformity among magnets. The actual limits and the solution for improvements are discussed. Finally a realistic schedule based on actual achievements is presented.     

Superconducting superferric dipole magnet with cold iron core for the VLHC

Magnetic system of the stage I Very Large Hadron Collider (VLHC) is based on 2 Tesla superconducting magnets with combined functions. These magnets have a room temperature iron yoke with two 20 mm air gaps. Magnetic field in both horizontally separated air gaps is generated by a single, 100 kA superconducting transmission line. An alternative design with a cold iron yoke, horizontally or vertically separated air gaps is under investigation. The cold iron option with horizontally separated air gaps reduces the amount of iron, which is one of the major cost drivers for the 233-km magnet system of future accelerator. The vertical beam separation decreases the superconductor volume, heat load from the synchrotron radiation and eliminates fringe field from the return bus. Nevertheless, the horizontal beam separation provides lowest volume of the iron yoke and, therefore, smaller heat load on the cryogenic system during cooling down. All these options are discussed and compared in the paper. Superconducting correction system combined with the magnet that allows increasing the maximum field is also discussed. Preliminary cost analysis is performed for all these options.     

Superconducting coil development and motor demonstration: Overview

Superconducting bismuth-cuprate wires, coils, and magnets are being produced by industry as part of a program to test the viability of using such magnets in Naval systems. Tests of prototype magnets, coils, and wires reveal progress in commercially produced products. The larger magnets will be installed in an existing superconducting homopolar motor and operated initially at 4.2K to test the performance. It is anticipated that approximately 400 Hp will be achieved by the motor. This article reports on the initial tests of the magnets, coils, and wires as well as the development program to improve their performance.     

Superconducting Magnets and Cooling System in BEPCII

A pair of dual-purpose superconducting quadrupole magnets and a superconducting detector solenoid were fabricated and installed in Beijing Electron-Positron Collider Upgrade (BEPCII). The magnets are symmetrically inserted into the BESIII detector with respect to the interaction point. They are identical, iron-free, non-collared, multi-layered and active shielded superconducting magnets for the micro-beta focusing at the interaction region of the collider rings. Each quadrupole magnet is composed of seven coils at different operating currents wound layer by layer on a common cylindrical support. The magnet has an overall effective length of 0.96 m and provides a good field aperture of 65 mm in diameter. They are cooled by supercritical helium in order to eliminate the flow instabilities in constrained cooling channels. The BESIII superconducting solenoid magnet was designed to provide an axial magnetic field of about 1.0 T over the tracking volume and to meet the requirement of particle momentum resolution to particle detectors. A single layer of coil, in-direct cooling by forced two-phase helium, high purity aluminum based stabilizer and NbTi/Cu superconductor is adopted for the solenoid. The solenoid is 3.4 m in diameter and 3.89 m in length. This paper presents the design of the superconducting magnets in the BEPCII as well as their cryomodules. The cooling system for the magnets is also discussed.     

Coil size and geometric field quality in short model dipoles forLHC

We have measured the magnetic field at room temperature and at 1.8 K on more than twenty, 1-m long, single aperture LHC superconducting dipole models. The magnets feature either a 5-block coil geometry or the baseline 6-block geometry foreseen for the LHC. Comparison of warm and cold measurements show that the coil geometry is essentially unchanged during cooldown. We have therefore used mechanical measurements taken on the coil and collars during assembly to estimate the azimuthal coil length. Based on these measurements we show here that the sensitivity of allowed harmonics on coil size is in good agreement with the prediction obtained from the numerical model used for designing the LHC magnets     

16th International Conference on Magnet Technology (MT-16 1999)

The following topics were discussed: the superconducting magnets for the Large Hadron Collider; superconducting magnets for the Relativistic Heavy Ion Collider; undulators; the RIKEN cyclotron; HERA magnets; high field dipole magnets; detector magnets; the CMS detector; the ATLAS detector; high field solenoid magnets; fusion magnets; magnet electrodynamics; magnetic resonance; energy storage; superconducting power transformers; permanent magnets; magnetic levitation; low temperature superconductors; cable in conduit superconductors; high temperature superconductors; current leads and cryogenics     

Design of the magnetic channels for the RIKEN superconducting ring cyclotron

Special designs have been adopted for the magnetic channels of the injection and extraction systems of the RIKEN Superconducting Ring Cyclotron (SRC). These magnetic channels are installed in the chambers between upper and lower coils of the sector magnets of the SRC, and superimpose additional magnetic fields on the base field of the sector magnets to inject or extract various beams. Maximum magnetic rigidity of the beam is considerably higher than that of conventional cyclotron, and the spaces to install the magnetic channels are limited by the size of the chambers and turn separation of the beams. Therefore powerful and compact magnetic channels are required. And besides, all magnetic channels were specified as normal-conducting magnets to reduce fabrication cost and to assure reliability. However, it is difficult to generate high magnetic fields by conventional normal-conducting magnetic channels with conductors only. Therefore, novel designs for powerful and compact normal-conducting magnetic channels were devised by use of iron as efficiently as possible. Detail designs are in progress.     

Superconducting Magnetic Filter: Performance, Recovery, and Design

Due to the development of superconducting magnets, the magnetic filtration process is now undergoing its biggest evolution since its conception. In Japan, the first industrial superconducting magnetic filter has been successfully applied for factory wastewater treatment. Much effort in both theory and practice is needed to further contribute to the new developments of this high gradient magnetic filtration process. In this substantial review, we have collected the most important theoretical and practical data about magnetic filtration, its recovery and design to establish a good framework for further development of this amazing technology.     

Superconducting electrical machinery

Recent developments in superconductors have made possible the application of superconductivity in the windings of electric machinery. Extensive studies have been made, and several experimental superconducting machines have been built and tested. In synchronous machines, the higher currents and flux densities in a superconducting field winding offer savings in size, weight, and cost. In homopolar machines, the greater flux densities make possible higher terminal voltages. This, with the development of liquid-metal current collection, makes homopolar machines a feasible alternative to conventional dc machines for high-power applications.     

Magnetic field characteristics of the low-beta quadrupole magnets, MQXA, for LHC

As a part of the collaboration program between CERN and KEK for the LHC, KEK has developed a superconducting low-beta quadrupole magnet, MQXA. KEK will supply 18 MQXA magnets, and 16 magnets will be installed in total in the four interaction regions. The cold tests of 13 magnets have been completed. Systematic field measurements were performed on these magnets, and these 13 magnets had satisfactory field quality for the requirement of beam optics. This paper describes the magnetic field behavior of the 13 MQXA magnets from the viewpoint of accelerator operation.     

Technical innovations for a high-gradient quadrupole electromagnet intended for high power proton drift tube linacs

The IPHI project includes a 352 MHz drift tube linac (DTL) to accelerate a 100 mA cw proton beam from 5 to 10 MeV (1 MW beam power). The main challenge of such a structure is to house a strong gradient quadrupole (QP) in the very reduced space of the first drift tubes (DT). Having chosen not to use permanent magnets, the goal is to design 4.70 T integrated-gradient QP less than 50 mm long with 90 mm maximum outer radius and an aperture as large as possible to minimize beam losses. Two DT have been designed and built with different QP magnets for the low energy end of the IPHI DTL. The first one is based on conventional magnets with hollow conductors and high-permeability cobalt-iron alloy for the poles and yoke. Two separate cooling circuits are used for the DT and the magnet coils. A second design has been done to make profit of the full space available inside the DT and to reduce their manufacturing cost as much as possible. A single water flow is used to cool simultaneously both DT body and QP coils made up of full (nonhollow) conductors.     

Status of the production of the LHC superconducting corrector magnets

The Large Hadron Collider (LHC) will be equipped with a large number (6400) of superconducting corrector magnets. These magnets are powerful, with typical peak fields of 3-4 T on the coils, but at the same time compact and of low cost. There are many types: sextupoles, octupoles and decapoles to correct the main dipole field, dipoles, quadrupoles, sextupoles and octupoles to condition the proton beams and several nested correctors from dipole to dodecapole in the inner triplets. The sizes vary from 6 kg, 110 mm long, nested decapole-octupole spool pieces to 1800 kg, 1.4 m long, trim quadrupoles. The fabrication of the 11 different types of magnets is assured by 10 contracts placed at 6 firms, two of which are in India. A number of magnets are now in series production, others in their pre-series production. The paper describes the present state of the fabrication and the testing of these magnets.     

Coupling Current and AC Loss in LHC Superconducting Quadrupoles

One of the issues for the operation of the LHC accelerator at CERN are the field errors generated by coupling currents in the superconducting cables of the main dipoles and quadrupoles, especially during the initial phase of the energy ramp from injection conditions. Coupling current effects have already been measured in the superconducting dipoles, and results are reported elsewhere. This paper reports similar measurements that we have recently performed on different types of LHC superconducting quadrupoles (arc quadrupole, dispersion suppressor and matching section quadrupoles) to quantify the above effects and compare them to the values specified from the beam tolerances. Loss and field errors due to ramping are mainly determined by the contact resistance between the strands of the magnets cables. In this paper the is calculated for several quadrupoles measured using both the measured energy loss and the magnetic field errors during ramping of magnets.     

High temperature superconductivity: Magnets and applications of naval interest

The Navy has had a long standing interest in power applications of superconductivity. Recent advances in high temperature superconducting (HTS) materials have caused the Navy science and technology community to assess the potential of HTS magnets for Naval applications. A program has begun to test HTS conductors and magnets in order to determine realistic performance expectations from which to determine proper systems integration. This paper presents some early results of industrially produced HTS magnets and discusses possible Naval applications. Speculative application toward magneto-hydrodynamic (MHD) propulsion is also discussed-specifically with respect to HTS materials.     

Superconducting materials for large scale applications

Since the 1960s, Nb-Ti (superconducting transition temperature T/sub c/=9 K) and Nb/sub 3/Sn (T/sub c/=18 K) have been the materials of choice for virtually all superconducting magnets. However, the prospects for the future changed dramatically in 1987 with the discovery of layered cuprate superconductors with T/sub c/ values that now extend up to about 135 K. Fabrication of useful conductors out of the cuprates has been difficult, but a first generation of silver-sheathed composite conductors based on (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ (T/sub c//spl sim/110 K) has already been commercialized. Recent progress on a second generation of biaxially aligned coated conductors using the less anisotropic YBa/sub 2/Cu/sub 3/O/sub 7/ structure has been rapid, suggesting that it too might enter service in the near future. The discovery of superconductivity in MgB/sub 2/ below 39 K in 2001 has brought yet another candidate material to the large-scale applications mix. Two distinct markets for superconductor wires exist-the more classical low-temperature magnet applications such as particle accelerators, nuclear magnetic resonance and magnetic resonance imaging magnets, and plasma-containment magnets for fusion power, and the newer and potentially much larger market for electric power equipment, such as motors, generators, synchronous condensers, power transmission cables, transformers, and fault-current limiters for the electric utility grid. We review key properties and recent progress in these materials and assess their prospects for further development and application.     

Finite element modeling of the powder-in- tube process for manufacture of BSCCO-2212 superconducting wires

High-temperature superconductors have recently attracted a great deal of attention owing to their potential use in a variety of applications including power generators, superconducting magnets for mine sweepers or ship propulsion motors, and magnetic levitation transportation systems. The powder-in-tube (PIT) process has emerged as one of the most promising and economically feasible techniques to produce long lengths high-T_c oxide based superconducting wires. The PIT method involves multi-pass wire drawing followed by rolling and heat treatment. This work focuses on the development of finite element models to simulate the PIT drawing process for fabrication of silver sheathed Bi-2212 superconducting wires. The numerical models were used to predict the density of the oxide powder, the wire drawing forces, and the silver-oxide ratio during drawing. A cap-type pressure dependent constitutive equation was implemented in the model to simulate the powder behavior. The model incorporated experimentally obtained material data for the silver and powder. Data from wire drawing experiments were used to verify model predictions.