CORE Metadata, citation and similar papers at core.ac.uk

Provided by CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

CERN LIBRARIES, GENEVA ‘: ||l||\ll|lllll|Ull\I\ Nllllllllllllllllllllll CERN—AT-94-43 CERN AT/94-43 (MA) / LHC Note 298 .5%. ii {C13

Design Status of Superconducting Magnet for the LHC

LHC Magnet Team, presented by N. Siegel

Abslgact

The LHC is a superconducting accelerator-collider to be installed in the LEP tunnel at CERN for high energy collisions in the multi~TeV range of p-p, heavy ions and e-p particle beams. The collider consists mainly of a ring of twin-aperture high field superconducting magnets operating in superfluid helium at 1.9 K. The layout of the machine and of the magnets will be described, which comprises 1250 dipoles of 14.2 m magnetic length and 400 quadrupoles of 3 m magnetic length. To reach the nominal 7 TeV proton beam energy, the main dipoles will operate at a field of 8.36 T and the main quadrupoles at a gradient of 210 T/ m. In total, more than 10000 superconducting magnets, including the regular arcs, the dispersion suppressors and the straight sections, must be built. The general design of these cryomagnets is described. Also the model and prototype work, together with the results achieved so far are presented. Among the short dipole models, one assembled at CERN with industrially made coils reached an ultimate field of 10.5 T and of the 10 m long industry made dipoles, the first reached the present nominal field without training quenches, showing that accelerator operation at that field is at hand.

14th Conference on Charged Particle Accelerators, Institute for High Energy Physics (HEP), Protvino, Russia, 25-27 October 1994

Geneva, Switzerland 2 February, 1995 OCR Output DESIGN STATUS OF SUPERCONDUCTING MAGNETS FOR THE LHC LHC Magnet Team, presented by N. Siegel CERN, European Organization for Nuclear Research, CH-1211 Geneva 23

Abstract

The LHC is a superconducting accelerator-collider to be installed in the LEP tunnel at CERN for high energy collisions in the multi-TeV range of p-p, heavy ions and e-p particle beams. The collider consists mainly of a ring of twin-aperture high field superconducting magnets operating in superfluid helium at 1.9 K. The layout of the machine and of the magnets will be described, which comprises 1250 dipoles of 14.2 m magnetic length and 400 quadrupoles of 3 m magnetic length. To reach the nominal 7 TeV proton beam energy, the main dipoles will operate at a field of 8.36 T and the main quadrupoles at a gradient of 210 T/m. In total, more than 10000 superconducting magnets, including the regular arcs, the dispersion suppressors and the straight sections, must be built. The general design of these cryomagnets is described. Also the model and prototype work, together with the results achieved so far are presented Among the short dipole models, one assembled at CERN with industrially made coils reached an ultimate field of 10.5 T and of the 10 m long industry made dipoles, the first reached the present nominal field without training quenches, showing that accelerator operation at that field is at hand.

1. INTRODUCTION

The CERN Large Hadron Collider essentially consists of a ring of high field superconducting magnets installed in the 27 km of the LEP timnel at CERN. The general design of this machine has been reported in several conference papers [1], [2], and a base-line design report was published in November 1993 [3]. The main parameters of the LHC for p-p collisions are given in Table I.

TABLE1 MAIN PA1zAM1;r1zRs o1=rr—m LHC rox PRo·roN-PRoroN OPERATION

Centre-of-mass collision energy (T eV) 14.0 Dipole field 8.36 Lurninosity (cm‘2s‘1) 1034 Injection energy (T eV) 0.45 Circulating current/beam (A) 0.53 Particles per beam 4.7 x 1014 Stored beam ener 332

An important asset of the LHC is that the existing accelerator infrastructure of CERN will provide the injection beams with the required characteristics with only a few additions to the present installations. Since the injector chain is composed of fast cycling classical accelerators, the LHC can be filled in a relatively short time of about 7 min, reducing the time at injection level, where the beams are more sensitive to perturbations like those coming from persistent currents. The layout of the LHC consists, as for LEP, of eight arcs separated by so·ca1led long straight sections. The two counter rotating beams circulate in two separate, horizontally spaced, magnetic channels. To achieve compact high field magnets, compatible with the cross-sectional dimensions of the existing LEP tunnel, they are designed of the so-called "two-in-one" structure, incorporating the two beam channels in the same yoke and cryostat. Such a configuration, first studied at Brookhaven National Laboratory for fields up to 5 T at 4.2 K, results in smaller cross-sectional dimensions and more economic solution. [4]. A perspective view of the "two-in·one" dipole is shown in Fig. 1. The LHC magnets use N'bTi superconductors operating in a static bath of superfluid helium at 1.9 K pressurized at 1 bar [5]. The benefits of the superfluid helium are its very large heat conductivity and ability to penetrate through insulation porosities, thus permeating and cooling the conductor. By this mechanism heat dissipated in the conductor due mainly to beam losses and also to ramping and resistive losses is to be conducted away to the cold source within a limited temperature margin of the cable, which is 1.2 K at 8.65 T for the inner layer. Experiments studying heat transport of different types of insulated cables cooled by superfluid helium have been carried out at CEN, Saclay, (F), in view of optimizing the insulation parameters [6]. On the other hand, at 1.9 K, the thermal capacity of materials and of the cables are reduced by about an order of magnitude with respect to the ones at 4.2 K, inducing higher and faster temperature rises for a given heat deposition. The magnets become thus more sensitive to quasi-adiabatic heat development and propagation in the conductors caused by sudden motions. Considering further the high forces and the high stored electromagnetic energy, proportional to B2, underline the great care required in the construction of the force-retaining structure to prevent premature quenches.

2. LHC LAYOUT AND LATTICE

The two interlaced LHC rings follow very closely the LEP geometry, in particular both machines must have the same revolution time to allow to convert them later into an e-p collider. The LHC, like LEP, is made of 16 half-octants, each of them 1.7 km long and made up of a long arc with a mean radius of 3.5 km, followed by the dispersion suppressor and a long straight section. The octant spans from mid-arc to mid-arc with services feeding it from the pit at the centre of the long straight section. The option to feed the LHC from the four even access points is being studied now in detail, due to its important cost savmg aspect. OCR Output As a result of funhcr optimization of thc machine from the point of vicw of beam stability, operational reliability, maximum dipole occupancy in the arcs and cost, the regular lattice is now based on 23 cells per half octant with the powering of the main quadrupoles separate from that of the dipoles, thus enabling to suppress the timing quadrupoles. The schematic layout of the new regular half-cell is shown in Fig. 2 and includes three long dipoles and one short suaight section about 6 m long. The dipole length is stretched to 14.2 m and the nominal Held is 8.36 T for a 7 TeV proton beam. The short straight section includes the 3 m long main quadrupole working at a gradient of 210 T/m for 90° phase advance, two corrector magnets one being either a skew quadrupole or an octupole, the other a combined sextupole/dipole, a beam monitor and the cryogenic service module. Attached to each main dipole are one small sextupole and one small decapole corrector to compensate in situ the tield errors introduced by the main magnets. The effect of these Held errors on the dynamic aperture has been reduced by enlarging the inner coil diameter from the previous 50 mm to 56 mm.

53.239

E ze 14.20 14.20 14.20 S

WEE MB MB MB

Dipole magnet MQ: Lattice quadmpoles MQSC: Skew quadrupole MQC: Landau octupole MSB: Combined sextupole and dipole corrector BPM: Beam Position Monitor - 0 —: Local Sextupole or Decapole Corrector

Fig 1. Perspective View of the ··tWO_in_Onc·· dipole Fig. 2: Schematic layout of the LHC half-cell with 23 periods per octant

3. THE CRYOMAGNETS

The LHC magnets represent a total of about 1400 tons of conductor of which 400 tons of high homogeneity NbTi alloy. The total mass to be kept at 1.8-1.9 K is 30000 tons covering about 24 km of the circumference of LEP. The main features and parameters of the magnets are outlined below.

3.1 Main dipole magnets

3.1.1 Design features: the design of the dipoles has to meet the following basic requirements: - Operational field of 8.36 T. Magnetic length of 14.2 m. Coil inner diameter of 56 mm. Distance between the axes of the apertures of 180 mm. Based on existing experience and on the given set of requirements, a new design was worked out, of which the main parameters are listed in Table H and a cross-section is shown in Fig. 3. The fabrication of magnets of this design is now launched, as explained in Section 4.1. The cross-section of the already built and tested 10 m dipoles of 50 mm aperture of the previous design is shown for comparison in Fig. 4. With respect to the previous design, a certain number of changes have been introduced in the dipole design to match the requirements of increased apemire and lower operational field, and to make the construction simpler, better adapted to series production and more economic. The coil is made in two layers. The cable width is reduced from 17 mm to 15 mm, with different thickness in the two layers to obtain the desired grading of current density. The Cu/Sc ratio is different in both strands and chosen from stability and protection considerations. The main parameters of the new cables are listed in Table HI. The present characteristics are based on the previous experience of fabricating about 15 tons of 17 mm wide cable. The critical current densities indicated are at 3 o' below the average value obtained previously. Strand and cables of the new design have already been ordered and delivered to CERN. The parameters which could vary in the long term are the amount of Cu in the strands and a betrer control of the copper RRR in the outer layer. A follow-up programme is established in collaboration with the US laboratories. The conductor insulation is made up of two layers of half overlapped polyimide film, followed by a wrap of glass fibre impregnated with b-stage epoxy spaced by 2 mm. As an altemative, this latter layer will be replaced by an adhesive coated polyimide film and the insulation tested on a short magnet of l m and a long magnet of 10 m. The field distribution was optimized with a coil made of 5 blocks, instead of 6, thanks to the fmer discretization of tums with the new somewhat thinner conductor. Both layers are separated by a spacer with channels to ensure helium circulation. The ground insulation is composed of several layers of polyimide film and includes protection heater strips. A metallic sheet is placed between the insulated coils and the collars to protect the insulation during collaring and bridge the gaps between the collars. OCR Output ¤sao ¢sao

@ , 5 , - . {I} @ Kg`? ·@ O ¢120.2q | R1005 y aw 18.6 — $ _ :-\ e “ L ¢»\-J •· Q. § lib ` "* M M ··‘* $ -·{j fM V· F- V —·`—’J ·® @+He}—-- -¢é L , -\~—--»». . [email protected]. ~ _.-._? C!* L. —~—· \\ i" E 4 mJ\, M., E , §Q¢55 "Q ° /4 §L v {; 180 \ - s¤.-.;.-.--- ¤¤¤

@ [ \ @ C- ` “

@ " Q

1. Beam screuy 2. Beam pipe, 3. Superconducdng coils, 4. N on-magnetic collars, 5. Iron Yoke , 6. Shrinking cylinder / Hell vessel, 7. 5.c. bus bars, 8. Heat exchanger pipe, 9. Gap conuol spacer. Fig. 3: Dipole cross—secti0n of thc new design (0 56 mm) Fig. 4: Cross·secti0n of tested 10 m dipole (¢ 50 mm)

The collars are in high strength aluminium alloy 3 mm thick and common to both apertures. To reduce the number of yoke parts, they are of the so—cal1ed racetrack shape and include a magnetic iron insert to maintain the field unifomiity between injection and collision tield level. These inserts, which have twice the thickness of the collars, are also used to clamp firmly the collars in pairs. The yoke, made in two parts, is vertically split, and held together by two welded half shells forming the outer shrinking cylinder. To match the curvature of the beams, the dipoles will be curved with a radius of 2700 m, locked into the assembly by the welded shrinking cylinder.

3.1.2 Cryostat and cooling. The cryostat (Fig. 5) has two layers of thermal insulation at 50 and 4.5 K to intercept and limit the heat influx into the 1.9 K cold mass [7]. The helium tank, which encloses the cold mass, is made of the shrinhng cylinder as outer shell and of the vacuum chamber as inner wall, closed at both ends by welded covers carrying the interconnection pipes between magnets. The cold mass hlled with superfluid helium is cooled by two—phase low pressure helium circulating in a heat exchanger tube installed in a 55 mm diameter hole placed above the axis of the iron yoke.

3.1.3 Field distribution. Calculated field errors arising from the magnet geometry, iron saturation and including the computed sextupole and decapole errors due to persistent currents (- 3.6 x 10*4 and 0.2 x 10*4 respectively) at injection field (~0.56 T) are shown in Fig. 6. The latter errors will be corrected with small sextupole and decapole magnets placed at the dipole ends. Current sharing among the strands distorts the magnetic field during ramping. ’I'his eiect would be acceptable at injection with an interstrand contact resistance between 6 and 10 p£2. A number of strand coatings of different materials and of resistive barriers are under invesdgation. Measured values with SnAg5% coated strands range from 1.5 to 8 p.Q.

TABLE H TABLE IH Du>o1.E PARAMmzRs DIPOLE STRAND Arm CABLE Cmuzacrmusrics

Operational field 8.36 T Inner Layer Outer Layer Coil aperture 56 mm S zrand Magnetic length 14.2 m Diameter (mm) 1.065 0.825 Operating current l 1'500 A Cu/Sc ratio 1.6 1 .9 Operating temperature 1.9 Filament size (mm) Coil turns per beam channel 82 Twist pitch (mm) 25 25 Distance between aperture axes 180 mm Critical current (A) Outer diameter of cold mass 580 Him at l0T,1.9K 2510 Overall length of cold mass ~ 15 at9T. 1.9K 2 370 Outer diameter of cryostat 980 Il`lHl Cable Overall mass of cryomagnet 31 Number of strands 28 36 Stored energy for both channels 7.4 Cable dimension Self-inductance for both channels 119 mH width (mm) 15.0 15.0 Resultant of e-magnetic forces in the thin/thick edge (mm) 1.72/2.06 1.34/1.60 fust coil quadrant 2,Fx (1.70 MN/m) 24.0 Transposition pitch (mm) 110 100 inner layer ZFY (- 0.14 MN/m) — 2.0 Critical current (A) outer layer XFY (· 0.60 MN/m) - 8.5 at 10 T, 1.9 K 2 13750 Axial e-magnetic force on magnet ends 0.52 at 9 T. 1.9 K OCR Output 2 12880 3.1.4 Quench protecnkm. The quench protection system [8] is based on the so—ca11ed "cold diode" concept, which allows the current to by-pass a quenching magnet, while the still superconducting magnets are rapidly de·excited. The diodes, installed in the cold mass, will be of the thin base epitaxial design, tested to be radiation resistant, with a prolonged service life if annealed by carrier injection and occasionally warmed-up to room temperature. Due to the large stored energy of the dipoles (500 kJ/m) coupled to the relatively low natural quench propagation speed in the cables (10 to 20 m/s), a sensitive quench detection is needed to fire snip heaters which will spread the quench over the full volume of the magnet.

3.2 Main lattice quadrupoles

The main quadrupoles are designed for a gradient of 220 T/m and for a magnetic length of 3.0 m. Their construcuonal features are very similar to the already made prototypes [9]. The two layer coil is wound in the pancake style from the same cable, thus avoiding interlayer splices and the related ohmic losses. The same cable, (or at least strands) as for the dipole coil outer layer is used. The collars are in austenitic steel and sustain the full electromagnetic forces. Both quadrupoles are placed in a common iron yoke, sdffened by an outside rigid tube, in a similar "two-in-one" coniigtuation as the dipoles.

3.3 Insertion magnets

Of the 166 special quadrupoles in the insertion regions, 114 are of the lattice quadrupole cross-section, but of three different lengths. The other ones have an enlarged aperture of 70 mm to ensure a field quality compatible with the required LHC performance. A novel design is used to obtain the 250 T/m at 1.9 K with NbTi cables, consisting in a suitable combination of high and low current density coil blocks. In the experimental insertions these quadrupoles are single aperture 5.5 m long magnet modules used in the irmer focusing niplets [10], whereas in the other insertions these quadmpoles are in the two-m-one version. Additional magnets needed in the long straight sections include beam separation/recombination dipoles, skew quadrupoles, dipole correction magnets and special dipoles for the dump insertion. Most of these elements are of the same type as for the regular lattice of the machine, however some of the 192 skew quadrupoles and of the correction dipoles will need an increased aperture of 70 mm.

3.4 Other magnets

A large number of correction magnets are required: trim quadmpoles needed to tune the series connected lattice type quadrupoles of the insertions, skew quadrupoles, octupoles, sextupoles and decapoles. For all these magnets a reliable design has been worked out and for the more critical of them, models and prototypes have been made and tested [11], [12], [13]. In this respect, the experience gained with the prototype tuning quadrupole is directly applicable for the trim and skew quadrupoles.

4. R & D Przocnmvuvm

The programme, undertaken by CERN in collaboration with national institutes and universities and with an important participation of industrial firms was mainly focused on standard-cell components, in particular on the dipole and quadrupole, but included also other magnets and related items.

K @4% \\ X/e Systematic multipoles b2, b3, b4 and b5 incl. persistent current effects for new dipole af/E ·> rv-j

• e __ _ q \ \_____....._ *_ \ • 9& S ‘i*· t § tl \ ‘‘*‘ CI·£¥§¤-]r·*’=2' -•-b2 —•—¤s -•—¤4 —¤—¤s

i?"..-.f--.TTTTTT__Q ..... 7:*;

1. Beam screen, 2. Beam pipe, 3. Supaconductirrg coils, 4. Non

magretic collars, 5. Iron yoke, 6. Shrinldng cylinder! Hell vessel, O 2 s e ro 7. Sc.. bus-bars, 8. I-lat exchanger pipe, 9. Radiative insulation, Dipole Held in Tesla 10. Thermal shield (55to 75 K), 11. Vacuum vwsel, 12. Support post, 13. Aligtmem target, 14. 1.8 K GHe pipe, 15. 20 K GI·Ie pipe, 16. 4.5 K GI·le pipe, 17. 2.2 K GHe pipe, 18. 50+75 K Gl-le pipe. Fig. 6: Systematic multipoles bg, bg, ba, and bg in the dipole as flmcucn of md Fig. 5: Cross-section of LHC dipole and cryostat OCR Output 4.1 Dipoles

The R & D effort covers the superconducting cables, the single and twin-aperture model magnets and the 10 m long magnets. 4.1.1 Superconducting cable. The total amount of 17 mm cable developed and fabricated by tive European companies is 24 km for the inner layer (26 strands of ¢ 1.29 mm) and 42 km for the outer layer (40 strands of ¢ 0.84 mm) and satisfies all main technical requirements giving confidence that the required quality can be maintained in mass production. 4.1.2 Model magnets. Ten models, 1.3 m long (4 single-aperture units and 6 twin-aperture units) of 50 mm aperture have been made and tested [14]. Eight of these magnets had a short sample field around 10 T. Different variants in conductors (e.g. unsoldered, partially soldered and soldered), collar type and material, yoke structure and outer retaining cylinder were tested [15]. Generally, these models have behaved in a very similar way, achieving short sample field with little or no training at 4.2 K, but showing training behaviour at 1.8 K [16]. The ultimate field (between 9.7 and 10 T) was generally obtained after a relatively large number of training quenches, mainly above 9.5 T. Most of the quenches in these magnets occurred in the end regions, where the field is lower than in the straight part, but conductor clamping less well controlled. The most recent model, assembled at CERN using industry made coils wound from a better performing last generation cable, reached the short sample field of 10.5 T. In this magnet, which was designed and assembled with high pre-compression in the coils, all training quenches were in the ends or in the splice region between inner and outer layer. The behaviour observed in the 10 m long magnets described below is the same or very similar to that observed in short models. Improvements in the performance of these critical regions in the final magnets can therefore be conveniently studied with short models. The programme at CERN foresees the construction of several single and twin-aperture models with coils made of the new 15 mm wide cable in view of optimizing parameters like shape and material of head spacers, conductor confmement in the ramp and splice region, cable insulation variants, axial compaction and compression of coil heads. Coils of the final design are being wotmd and the main components and tooling for assembly are on order. In parallel, the completion and testing of two twin-aperture magnets of 56 mm aperture, one using SSCL cables (Bs, = 9.4 T at 1.9 K) and the other special 16.7 mm graded cables (BSS = 10 T at 1.9 K) is planned end 1994 for the first and beginning 1995 for the second. 4.1.3 Ten metre long magnets. A first 10 m long magnet (TAP), made with HERA-type coils of 75 mm aperture mounted in a twin-aperture structure [17], successfully went to short sample field at 4.2 K showing the same behaviour as the single aperture HERA dipoles, thus validating the twin-aperture concept, and thereafter reached the short sample field of 8.3 T at 1.8 K in five training quenches. Of the seven 10 m long dipoles (50 mm aperture, 17 mm wide cable) of twin-aperture st:ructure ordered in industry, the first four have been delivered. The first two, funded by the "lstituto Nazionale di Fisica Nucleare" (INFN), Italy, have successfully passed the test and measurement campaign. The quench behaviour of the first magnet [18] is shown in Fig. 7. The first quench was at 8.67 T and the magnet did not retrain after a thermal cycle to room temperature. Training was stopped voluntarily at 9.6 T. The first quench of the second magnet, which had less performant cables, was at 8.3 T. It reached a field exceeding 9 T after a few quenches. All quenches occurred in the coil ends and nearby regions similarly as in the short models [19]. ln both magnets, no quench occurred in the regular straight part of the coils. The field distribution was measured in both magnets and showed that the multipole errors were close to the expected values in both apertures. The orientation and parallelism of the B vector was measured in both units: the first magnet exhibits some torsion (~ 10 mrad), the second a negligible amount, further in both the relative alignment of the B vector is bet1er than 0.2 mrad. The quench protection system worked satisfactorily and the maximum temperatures and voltages were as expected. The other three 10 m long magnets will be delivered to CERN in the coming months. The design of the 56 mm aperture magnets of the new cross-section is at an advanced stage, and 10 m and 14 m long collared coils and other components have already been ordered to industry. These new long magnets should be completed within the next two years, and are to be representative of the final design for the LHC. 4.1.4 Quadrupoles and other magnets. Two full size quadrupoles of 56 mm aperture and 3 m length have been designed, constructed and tested at CEN, Saclay (F) in the frame of a CERN -CEN Collaboration [20]. The design gradient was reached for the two magnets after very few training quenches (Fig. 8). Several models and prototypes of correction elements have already been successfully built, and others are under

atconsgruction. 1. K. A prototype tuning quadrupole (120 T/m, 0.8 m long) has been built in industry and successfully tested at CERN A prototype combined dipole/sextupole corrector (1.5 T, 8000 T/mz) has been built and tested with success at 4.5 K at RAL and at 1.8 K at CERN. At present, there are under construction in industry a single-aperture (¢ 70 mm) quadrupole model, 1 m long, for the low-beta insertions, to be completed and tested soon [21], one sextupole and one decapole spool pieces for the main dipoles and one superferric octupole corrector.

5. THE srrzmc rrzsr A short straight section prototype, including one of the lattice quadrupole prototypes built at CEN, Saclay, a full length cold mass, the cryogenic service module and the full cryostat was successfully assembled at CERN. This unit together with '‘ the first two 10 m dipoles were connected in series and attached to a cryogenic and electric feed box. Ihe elements are installed on a 1.4% slope, which is the maximum encountered in the LEP tunnel. This string which will be later completed with additional dipole magnets is now being cooled in view of tests which are to be representative of LHC operation. Testing the string will be an important milestone and will allow to check out primary systems in realistic and tunnel type conditions. OCR Output 18000 T Shqn sample curmnt 16000 Desiqn current -•—- ¤! -··I 1-$ 1 -• J- g·— LHC•• Obéfalion $ • FieldY •’<•BAT -§ c 14000 Jr ° •• 12000 1 A \ I • LHC nom. excitation 10000 J. [ N0 quer*h No quench ` No quench

Thennal After thermal qcle 8000 r J TF ';:nd‘/ cycle 6000 quench 4000 —#

O 2 4 6 8 10 12 14 2000 Ouadrup,1 I Ouadrupole2 [Ouench Number] 012 12345678910111213

Number of excitations Fig. 7: Quench history of first 10 m dipole Fig. 8: Quench history of the two prototype quadrupoles

6. CoNcLus1oNs

The fundamental technical choices for the consuuction of the LHC magnets have been validated, in pardcular: the two-in one configuration of main dipoles and quadrupoles, the operation in superfluid helium at 1.9 K, and the high Held levels needed for the required LHC performance. The successful behaviour of the recently tested two 10 m long dipole magnets confmn that the design is sound and that industrial fabrication of magnets with correct Held quality is feasible. The second phase of the R & D programme has already started with the construction in CERN of short models and in industry of full length collared coil assemblies and complete magnets of the new design.

AcKNowLE1>cE1vmN*r‘s

The LHC Magnet Team gratefully acknowledges the important contributions of several National Institutions and Laboratories, and the vital support of the superconductor and electro-mechanical Industry.

R1¤;r=ERENc1ts

[1] G. Brianti, "LHC Progress and Status", Proc. 1993 Particle Accelerator Conf., Washington, 3917, (1993). [2] LR. Evans, "Advaneed Tedrnology Issues in the LHC Project", presented at 1994 EPAC Conf., Londcm, June 1994. [3] The LHC Study Group, "The Large Hadron Collider Accelerator Project", CERN/AC/93-O3 (LHC), 1993. [4] D. Leroy, R. Perin, G. de R.ijk, W. ’I`homi, "Design of a High-Held Twin-aperture S.c. Dipole Model", IEEE Trans. on Magn., vol. 24, pp. 1373-76, March 1988. [5] Ph. Lebrun, "Superfluid Helium Cryogenics for the Large Hadron Collider Project at CERN," presented at ICEC 15 Conference, Genova, June 1994. [6] L. Bumod, D. Leroy, B. Szeless, B. Baudouy, C. Meuris, "lherrnal Modelling of the LHC Dipoles Ftmctioning in Supertluid Helium", presented at EPAC Conference, London, Jtme 1994. [7] J .C. Bnmet et al., "Design of LHC Prototype Dipole Cryostars", presmted at ICEC Conf., Kiev, June 1992. [8] L. Coull, D. Hagedom, V. Rernondino, F. Rodriguez Mateos, "U·lC Magnet Quench Protection System", IEEE Trans. on Magn., vol. 30, pp. 1742 45, July 1994. [9] J M. Baze et al., "Design and Fabrication of the Prototype Supereonducting Quadrupole for the CERN LHC Project", IEEE Trans. on Magn., voL 28, pp. 335-37, Ian. 1992. [10] A. Morsch, R. Ostojic, T.M. Taylor, "Progress in the System Design of the Inner Triplet of 70 mm Aperture Quadrupoles for the LHC Low-beta Insertions", presented at EPAC Conference, London, June 1994. [11] D.E. Baynham, R.C. Coombs, A. Ijspeert, R. Perin, "Design of Superconducting Corrector Magnets for LHC", IEEE Trans. on Magn., vol. 30, pp. 1823-26, July 1994. [12] A. Ijspeert et aL, "Test Results of the Prototype Combined Sextupole Dipole Corrector Magnet for LHC", IEEE Trans. on Applied Supereonductivity, vol. 3, No. 1, pp. 773-76, Mardi 1993. [13] H. Bidaunanga, L. Garcia Tabaxes, R. Perin, N. Siegel, "Design and Fabrication of the Prototype S.c. Tuning Quadrupole and Octupole Correction Winding for the LHC Project," IEEE Trans. on Magn., vol. 28, pp. 342-45, Jan. 1992. [14] R. Perin "Status of the Large Hadron Collider Magnet Development", presented at the 1993 MT13 Conference, Vicxoria, Canada (1993). [15] M. Bona, D. Leroy, R. Perin, P. Rohmig, B. Szeless, W. Thomi, "Desigry Fabrication Variants and Results of LHC Twin-Aperture Models", IEEE Trans. on Magn., vol. 28, pp. 338-41, Jan. 1992. [16] D. Leroy et al., "Test Results on 10 T LHC Superoonducting One-Meter Long Dipole Models", IEEE Trans.. on Applied Superconductivity, March 1993, vol. 3, No. 1, pp. 614-21. [17] M. Granier et al., "Perfcrmance of the Twin-Aperture Dipole for the CERN LHC", Proc. EPAC92 Conf., Berlin March 1992. [18] M. Bona etal., "Performance of the First CERNJNFN 10 m Long Superc. Dipole Prototype for the LHC”, presented at EPAC Conf., London, June 1994. [19] J. Billan, A. Siemko, L Waldders, R. Wolf, "Quench Localization in the Superc. Model Magnets of the LHC by Means of Pick-up Coils", presented at t.he ASC Conf., Boston, Oct. 1994. [20] P. Genevey et al., "Cryogenic Tests of the First Two LHC Quadrupole Prototypes", presented at the ASC Conf., Boston, Oct. 1994. [21] R. Ostojic, T.M. Taylor, G.A. Kirby, "Design and Construction of a One-Metre Model of the 70 mm Aperture Quadrupole for the LHC Low-beta Insertions", IEEE Trans. on Magn., vol. 30, pp. 1750-53, July 1994.