Fabrication of the pre-series wide aperture superconducting quadrupoles for the LHC insertions

Individually powered superconducting quadrupoles with a coil bore of 70 mm will be installed in the LHC insertions, in areas where increased geometrical acceptance and improved field quality are required. The quadrupoles feature a four-layer coil, designed on the basis of two graded 8.3 mm wide Rutherford-type NbTi cables. The magnets have a magnetic length of 3.4 m and a nominal gradient of 160 T/m at 4.5 K and 3610 A. A total of 26 quadrupoles are in production at ACCEL Instruments (Germany). In this report, we present the experience in fabrication of the pre-series magnets and the results of the initial qualification tests.     

Design and fabrication of a 1 m model of the 70 mm bore twinaperture superconducting quadrupole for the LHC insertions

For reasons of geometrical acceptance, 70 mm bore twin aperture quadrupoles are required in the LHC insertions. For an operating gradient of 160 T/m at 4.5 K, a design based on a four layer coil wound from two graded 8.2 mm NbTi conductors has been developed. Three 1 m single aperture quadrupoles of this design have been built and successfully tested. Thereafter, the magnets have been disassembled and the coils re-collared using self-supporting collars. In this paper, we describe the design features of the twin aperture quadrupole, and report on the initial collaring tests and procedures for collaring and final assembly of the 1 m magnet     

Quenching behaviour of quadrupole model magnets for the LHC innertriplets at Fermilab

The US-LHC Accelerator Project is responsible for the design and production of inner triplet high gradient quadrupoles for installation in the LHC Interaction Region. The quadrupoles are required to deliver a nominal field gradient of 215 T/m in a 70 mm bore, and operate in superfluid helium. As part of the magnet development program, a series of 2 m model magnets have been built and tested at Fermilab, with each magnet being tested over several thermal cycles. This paper summarizes the quench performance and analysis of the model magnets tested, including quench training, and the ramp rate and temperature of the magnet quench current     

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.     

Design and assembly of the pre-series quadrupoles for the LHC insertions

The LHC insertions are equipped with several different types of individually powered superconducting quadrupoles. These units comprise several quadrupole magnets and orbit correctors, and range in length from 5.3 m to 11.3 m. In spite of the variety of types and interface requirements, the design of the quadrupoles is based on the same principle where two welded half-shells provide the rigidity and alignment of the magnets and serve as a helium pressure vessel. In this paper we present the mechanical design of the LHC insertion quadrupoles, describe the initial experience in the assembly of the pre-series units, and report on the alignment measurements.     

Development of superconducting tuning quadrupole corrector (MQT) prototypes for the LHC

The main quadrupoles of the Large Hadron Collider (LHC) are connected in families of focusing and defocusing magnets. In order to make tuning corrections in the machine a number of quadrupole corrector magnets (designated MQT) are necessary. These 56 mm diameter aperture magnets have to be compact, with a maximum length of 395 mm and a coil radial thickness of 5 to 7.5 mm, while generating a minimum field gradient of 110 T/m. Two design options have been explored, both using the "counter-winding" system developed at CERN for the fabrication of low cost corrector coils. The first design, with the poles composed of two double-pancake coils, each counter-wound using a single wire, superposed to create 4-layer coils, was developed and built by ACCEL Instruments GmbH. A second design where single coils were counter-wound using a 3-wire ribbon to obtain 6-layer coils was developed at CERN. This paper describes the two designs and reports on the performance of the prototypes during testing.     

Study of Kapton insulated superconducting coils manufactured forthe LHC inner triplet model magnets at Fermilab

Fermilab has constructed a number of 2 m model quadrupoles as part of an ongoing program to develop and optimize the design of quadrupoles for the LHC Interaction Region inner triplets. The quadrupole design is based upon a two layer shell type coil of multi-filament NbTi strands in Rutherford cable, insulated with Kapton film. As such, the coil size and mechanical properties are critical in achieving the desired prestress and field quality targets for the agent. Throughout the model magnet program, different design and manufacturing techniques have been studied to obtain coils with the required mechanical properties. This paper summarizes the structural material and coil mechanical properties, coil design optimization results and production experience accumulated in the model R&D program     

Inner triplet corrector package MQSXA for the LHC

The eight inner triplets of the LHC will each house a combined corrector magnet assembly, MQSXA, which comprises a skew quadrupole (MQSX) in line with nested skew octupole (MCOSX), octupole (MCOX), and skew sextupole (MCSSX) windings. These superconducting single-aperture magnet assemblies have a bore of 70 mm diameter, and the complete MQSXA assemblies are 530 mm long, have an outer diameter of 180 mm and an approximate mass of 90 kg. In the inner triplets the MQSXA assemblies are flanged to the end plate of the high gradient quadrupoles (MQX). This paper presents the main design features of the MQSXA and the experience gained with the prototype of the nested part of this magnet assembly, which has been built at CERN. The results of the training tests at 4.3 K and 1.9 K together with the cold magnetic measurements are given.     

Quench performance and mechanical behavior of the first Fermilab-built prototype high gradient quadrupole for the LHC interaction regions

As part of the US LHC program to provide high gradient superconducting quadrupoles for the LHC interaction regions, a 5.5 meter long prototype magnet has been built and tested horizontally in a production type cryostat at Fermilab. This prototype magnet was used to validate the mechanical and magnetic design, production fabrication and assembly tooling. The first prototype magnet has met the LHC requirements of operating at 215 T/m with excellent magnetic field harmonics. This paper summarizes the test results of this magnet, including quench tests and mechanical behavior over several thermal cycles.     

Performance Evaluation and Quality Assurance Management During the Series Power Tests of LHC Main Lattice Magnets

Within the LHC project, a series production of superconducting dipoles and quadrupoles has recently been completed in industry and all magnets were cold tested at CERN. The main features of these magnets are: two-in-one structure, 56 mm aperture, two layer coils wound from 15.1 mm wide Nb-Ti cables, and all-polyimide insulation. This paper reviews the process of the power test quality assurance and performance evaluation, which was applied during the LHC magnet series tests. The main test results of magnets tested in both supercritical and superfluid helium, including the quench training, the conductor performance, the magnet protection efficiency and the electrical integrity are presented and discussed in terms of the design parameters and the requirements of the LHC machine.     

Effects of Collar Permeability on the Field Quality of the Large Aperture Quadrupoles for the LHC

The LHC contains a number of large aperture quadrupoles (MQY) in the insertions. The acceptance of these magnets was based on warm magnetic measurements performed before delivery to CERN. During the series production of the MQY quadrupoles, the permeability of the collars drifted from the nominal value, and effects on the transfer function and multipole components became evident. To study the effects on the magnetic field, variable permeability of the stainless-steel collars as a function of local field and temperature was introduced into a numerical model. Comparing the results with measured data, we could isolate the contribution of permeability deviation on the magnetic field quality. The extrapolation of transfer function and field multipoles to operating temperature and current gives the necessary offsets, which are compared with measurements on a reduced set of magnets.     

Quench protection of the Fermilab-built LHC inner triplet quadrupole MQXB

High-gradient quadrupoles (MQXB) are being developed at Fermilab within the framework of the US-LHC Accelerator project for the LHC interaction regions. These 5.5-m-long magnets have a single 70-mm aperture and operate in superfluid helium at a peak gradient of 215 T/m. Magnet quench protection is provided by quench heaters installed on the outer surface of the coil. This paper reports the results of quench protection studies on the first full length MQXB prototype (MQXP01). The measurements from these tests as well as results from the 1.9-m-long model magnet program are combined with computer generated quench simulations to predict the MQXB performance under LHC operating conditions.     

Construction and measurement of the pre-series twin aperture resistive quadrupole magnet for the LHC beam cleaning insertions

CERN's Large Hadron Collider (LHC) requires 48 twin aperture resistive quadrupoles in the beam cleaning insertions. Canada is contributing these magnets to CERN in the framework of the TRIUMF-LHC collaboration contracts. A pre-series magnet was produced by Canadian industry and delivered in March 2001. This magnet incorporates important design changes that resulted from experience with a prototype magnet. The construction of this pre-series magnet and the measurements made at ALSTOM and at CERN are reported. A comparison is made between high precision pole distance measurements and the magnetic measurements performed with a rotating coil mole. Conclusions for series production and possibilities for multipole corrections are outlined.     

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.     

The electric quadrupole contribution to the circular birefringenceof nonmagnetic anisotropic chiral media: a circular waveguide experiment

Constitutive relations which include electric quadrupole terms, in addition to electric and magnetic dipole terms, are used to describe the “optical activity”, in particular the circular birefringence, of an anisotropic chiral medium which is nonmagnetic. The resulting permittivity and chirality tensors are then used to predict the rotation of the polarization plane of a linearly polarized wave propagating in a circular waveguide filled with the medium. The numerical predictions were tested by measurements between 2.4 and 4 GHz on a 2 m long artificial crystal in a circular waveguide and it was found that the rotation of the polarization was within 13% of the predicted value-good agreement after considering the possible sources of error. It is thus established that the effect of electric quadrupoles must be included when modeling the optical activity of anisotropic chiral media in the long wavelength regime. The anisotropic chiral media which are dealt with here can be classified according to the crystallographic point groups to which they belong, and they may therefore also be considered to be artificial crystals     

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.     

Study of the Thin Film Pulse Transformer

A great interest has been attracted in planar magnetic devices to miniature various electronic equipment including pulse transformers and inductors, especially for the IT electronics applications and ISND modem systems, such as switching converters and inverters in portable equipments[1~3]. In Internet system,the thin film pulse transformer, with the sandwich structure of core/coil/core and coil/core/coil, in general,will be fabricated directly on ceramics substrate by lithography and ion et…     

Multipoles of the SLS storage ring: manufacturing and magnetic measurements

The quadrupoles and sextupoles for the Swiss Light Source had severe requirements on the manufacturing tolerances and the alignment of their magnetic axis. The 306 multipoles were manufactured, and magnetically measured at BINP and after delivery also at PSI. The features of manufacturing and precise magnetic measurements of SLS multipoles are discussed.     

环烯烃共聚物空芯微结构太赫兹光纤的设计与制造

以环烯烃共聚物（cyclic-olefin copolymer,COC）材料为基质,设计、制造了一种空芯多孔包层太赫兹（THz）纤维。利用comsol 软件模拟了芯径为6 mm 的光纤在0.2~1.5 THz 波段的损耗特性,结果表明:在0.85~1.5 THz 波段存在多个低损耗频带,而且在0.85~1.1 THz 波段有低于3 dB/m 的三个窗口;特别是在0.99 THz,损耗达到0.208 dB/m。芯径为3 mm、4.8 mm 和6 mm 的光纤在0.8~1.5 THz 波段的损耗特性对比分析表明:该COC 微结构多孔包层空芯纤维的损耗随着光纤外径的增加而减小。把设计的太赫兹纤维外径放大7 倍达到7 cm,据此设计制造了光纤预制棒成型专用模具。借助热挤出成型方法得到了结构完整、孔洞表面光滑,长度为22 cm 的空芯多孔包层预制棒。利用该实验室独有的微结构光纤拉丝塔,成功获得了微结构保持完好的光纤样品。损耗分析结果表明:6 mm 芯径的光纤样品在1.27 THz 的平均损耗为2.175 dB/m,与该频率的理论损耗（1.95 dB/m）接近。