Albert Ijspeert

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.

Design and test of the prototype high T/sub c/ current leads for the Large Hadron Collider orbit correctors

The Large Hadron Collider (LHC) will need some 800 superconducting magnets to correct the orbit of the particle beams. These magnets will be individually powered and each needs a pair of current leads to the ambient temperature. To minimize the heat loss through these leads, the magnets have been designed for a very low current of about 25 amperes and the leads could be made with high T/sub c/ material. A theoretical study by the authors (see Adv. Cryog. Eng., vol.39, 1994) investigated different types of high T/sub c/ leads. Since then, a prototype has been built which combines a low heat loss with an extremely simple design. The design, the test set up and the results are described in this paper.<<ETX>>

Expected Advantages and Disadvantages of High-Tc Current Leads for the Large Hadron Collider Orbit Correctors

The Large Hadron Collider (LHC) will be equipped with some 800 superconducting magnets for the correction of the orbit of the particle beams. Each of these magnets will be individually powered and needs a pair of current leads to the ambient temperature. To minimise the heat load due to these leads, a very low operational current has been chosen of about 25 A. A theoretical study has been made of the advantages and disadvantages of leads partly made of high-Tc superconducting materials. The paper gives the results of these calculations comparing normal leads with different current lead options using high-Tc superconducting materials. The results are also immediately applicable to leads for any other current.

Further development of the sextupole and decapole spool corrector magnets for the LHC

In the Large Hadron Collider (LHC) the main dipoles will be equipped with sextupole (MCS) and decapole (MCD) spool correctors to meet the very high demands of field quality required for the satisfactory operation of the machine. Each decapole corrector will in addition have an octupole insert (MCO) and the assembly of the two is designated MCDO. These correctors are needed in relatively large quantities, i.e. 2464 MCS Sextupoles and 1232 MCDO Decapole-Octupole assemblies. Half the number of the required spool correctors will be made in India through a collaboration between CERN and CAT (Centre for Advanced Technology, Indore, India), the other half will be built by European industry. The paper describes final choices concerning design, materials, production techniques, and testing so as to assure economic magnet manufacture but while maintaining a homogenous magnetic quality that results in a robust product.

Design of superconducting corrector magnets for LHC

The Large Hadron Collider (LHC) will require a range of superconducting corrector magnets. This paper presents the design of sextupole and decapole corrector coils which will be included as spool pieces adjacent to each main ring dipole. The paper gives detailed 3D field computations of the coil configurations to meet LHC beam dynamics requirements. Coil protection within a long string environment is addressed and mechanical design outlines are presented. >

Development of a Superconducting Sextupole-Dipole Corrector Magnet

Each half cell of the proposed Large Hadron Collider (LHC) lattice [1] will be equipped with a 1.25 meter long superconducting corrector magnet which will combine a 4000 T/m2 sextupole and a 1.5 T dipole. The correction magnets of the two rings will be mounted in pairs in the cryostat of the main quadrupoles. The sextupole coil is wound from a solid, NbTi based, superconducting wire. The dipole coil is wound from a preassembled ribbon containing 12 parallel wires. The two concentric coils are precoropressed by shrink fitted aluminium rings. The yoke is simply a thick walled iron tube. The paper describes the magnet design, discusses the results of the field and stress calculations with emphasis on the superposition of the two types of field. It comments on the choice of the conductors and describes the developed fabrication techniques.

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. >

Test results of the prototype combined sextupole-dipole corrector magnet for LHC

The corrector magnet for the Large Hadron Collider (LHC) contains a 1.5-T dipole for orbit correction and a 8000 T/m/sup 2/ sextupole for chromaticity correction. The dipole has for compactness been mounted around the sextupole coil. A full-scale prototype of 1.3-m length has been fabricated and tested. The coils were first tested at 4.2 K. It appeared that the training of the impregnated coils could be strongly reduced by increasing the radial precompression. The coils were subsequently cooled to the operational temperature between 1.8 and 2 K and the field quality was measured with a harmonic rotating coil. The results of the tests show that the combined dipole-sextupole corrector magnet does meet the desired field strengths.<<ETX>>

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.

Development of Lithium Lenses at CERN

For the upgrading of the antiproton source as part of the ACOL project, strong lithium lenses with gradients of 500-1000 T/m are required. The characteristics of these lenses, like the current and field distributions and the temperatures and forces have been computed. Based on these studies, a novel lens design has been developed, including a lithium container of very high pressure resistance. For the proper filling of the lens a special circuit has been built to cast the liquid lithium under vacuum and high pressure into the container. The design and the assembly of a lens with a diameter of 2cm are described. Life tests of the lens in the laboratory have started. Presently, more than 104 current pulses have been accumulated at the required repetition rate of 2.4 s and peak currents of 320 kA without causing any failure of the lens.