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Fermilab is involved in the development of new generation high-field accelerator magnets using state-of-the-art Nb/sub 3/Sn strands produced using different technologies. Two 1-m long models-mirror configuration and dipole magnet-were fabricated recently at Fermilab based on powder-in-tube (PIT) Nb/sub 3/Sn strands with small effective filament size. This paper describes the parameters of superconducting strands and cable, the details of magnet design and fabrication procedure, and reports the results of PIT coil testing.

The US-LHC Accelerator Project is responsible for the production of the Q2 optical elements of the final focus triplets in the LHC interaction regions. As part of this program Fermilab is in the process of manufacturing and testing cryostat assemblies (LQXB) containing two identical quadrupoles (MQXB) with a dipole corrector between them. The 5.5 m long Fermilab designed MQXB have a 70 mm aperture and operate in superfluid helium at 1.9 K with a peak field gradient of 215 T/m. This paper summarizes the test results of several production MQXB quadrupoles with emphasis on quench performance and alignment studies. Quench localization studies using quench antenna signals are also presented.

Fermilab is developing and investigating different high-field magnets (HFM) for present and future accelerators. The HFM R&D program focused on the 10-12 T magnets based on Nb/sub 3/Sn superconductor and explored both basic magnet technologies for brittle superconductors-wind-and-react and react-and-wind. Magnet design studies in support of LHC upgrades and VLHC were conducted. A series of 1-m long cos-theta dipole models based on the wind-and-react technique was fabricated and tested. Three 1-m long flat racetracks and the common coil dipole model, based on a single-layer coil and react-and-wind technique, were also fabricated and tested. Extensive theoretical and experimental studies of electro-magnetic instabilities in Nb/sub 3/Sn strands, cables and magnets were performed and led to a successful 10 T dipole model. This paper presents the details of Fermilab's HFM program, reports its status and major results, and formulates the next steps for the program.

Several different shell type coils were made by using the 'wind-and-react' technique, installed in a mirror magnet configuration and tested at Fermilab. The results revealed that the previously suspect splice technique is adequate and is not responsible for the quench performance limitation. Cable instability is the preferred candidate, however this might be coupled with other effects since all of the experimental results cannot be explained exclusively with cable instability.

As part of the US-LHC Accelerator Project, Fermilab is producing fully cryostated assemblies that will be installed as the Q1, Q2 and Q3 optical elements for the LHC Inner Triplets. The main quadrupole magnets in the Q1 (LQXA) and Q3 (LQXC) assemblies are MQXA elements designed and fabricated by KEK and Toshiba, while those in the Q2 (LQXB) assemblies are MQXB quadrupoles designed and fabricated by Fermilab. The cryostat assemblies for all magnets are designed by Fermilab, and final assembly of the optical elements occurs at Fermilab. This paper describes the production test results for the second LQXB cryostat assembly.

The first one-meter long common coil dipole model (HFDC-01) has been fabricated and tested at Fermilab. This magnet has several innovative features such as: single-layer racetrack coils, a 22-mm wide 60-strand Rutherford-type cable made of 0.7-mm Nb/sub 3/Sn strands, and a stainless steel coil-support structure reinforced by horizontal bridges inserted between coil blocks. The model was instrumented with voltage taps, quench heaters, temperature sensors and strain gauges in order to monitor the quench origin, and to study mechanical and quench protection issues. This paper summarizes the model design parameters, the fabrication procedures and the test results.

Superconducting accelerator magnets must provide a uniform field during operation. However, the field quality significantly deteriorates due to persistent currents induced in superconducting filaments. This effect is especially large for the Nb/sub 3/Sn conductor being implemented in the next generation of accelerator magnets. A simple and inexpensive method of passive correction of the persistent current effect was developed and experimentally verified. This paper describes numerical simulations of the passive correctors and reports the test results.

Insulation is one of the most important elements of magnet design, which determines the electrical, mechanical, and thermal performance as well as lifetime of the magnet. The exposure to high radiation loads especially for the proposed LHC second-generation interaction region Nb/sub 3/Sn quadrupoles further limits the choices of the insulation materials. Traditionally Nb/sub 3/Sn magnets were impregnated with epoxy to improve both the mechanical and electrical properties. However, the acceptable radiation limit for epoxy is low which reduces the lifetime of the magnet. The paper presents the results of the feasibility study to replace epoxy with high radiation-resistant material during vacuum impregnation. The mechanical, thermal and electrical properties of samples impregnated with Matrimid were measured and compared with epoxy-impregnated samples.

A racetrack magnet, using Nb/sub 3/Sn superconducting cable reacted before winding, has been fabricated and tested at Fermilab. It consists of two flat racetrack coils, connected in a common-coil configuration, separated by a 5 mm thick fiberglass plate. Synthetic oil was used to prevent sintering of the strands during the heat treatment. The coils were wound and vacuum impregnated in the mechanical structure. The turn-to-turn insulation, consisting of Kapton/spl reg/ and pre-impregnated fiberglass tapes as wide as the cable, was wound together with the bare cable in order to form a continuous inter-turn spacer. The coils were instrumented with voltage taps, temperature sensors, spot heaters and quench heaters. The maximum current achieved was 12675A which is 78% of the short sample limit at 5.1 K (minimum temperature in the coil during 75 A/s ramp). Measurement of the temperature margin revealed a low degradation in the innermost turns. Quench performances at different temperatures and ramp rate effects have been measured and are presented and discussed.

Two short Nb/sub 3/Sn dipole models based on a single-bore cos-theta coil with a cold iron yoke were fabricated and tested at Fermilab. This paper summarizes the details of magnet design and fabrication procedure, and reports the test results including quench performance and quench heater studies, and the magnetic measurements.

A dipole magnet based on the common coil design, using prereacted Nb/sub 3/Sn superconductor, is under development at Fermilab, for a future Very Large Hadron Collider. This magnet has some innovative design and technological features such as single layer coils, a 22 mm wide 60-strand Rutherford type cable and stainless steel collars reinforced by horizontal bridges inserted between coil blocks. Both left and right coils are wound simultaneously into the collar structure and then impregnated with epoxy. In order to optimize the design and fabrication techniques an R&D program is underway. The production of cables with the required characteristics was shown possible. Collar laminations were produced, assembled and tested in order to check the effectiveness of the bridges and the validity of the mechanical design. A mechanical model consisting in a 165 mm long section of the magnet straight section was assembled and tested. This paper summarizes the status of the program, and reports the results of fabrication and test of cable, collars and the mechanical model.

This paper presents past results and future goals of the Nb/sub 3/Sn strand and cable R&D being performed within the High Field Magnet program at Fermilab. Research tools include a reaction site for Nb/sub 3/Sn, a Short Sample Test Facility, a Scanning Electron Microscope, and a 28-strand cabling machine. Strands of various designs and diameters produced with the Internal Tin, Modified Jelly Roll, and Powder-in-Tube methods, and several Rutherford-type cables were studied.

Fermilab is involved in the development of high field superconducting accelerator magnets for different applications based on Nb/sub 3/Sn superconductor. Accelerator magnets have to withstand thousands of thermal and excitation cycles, significant mechanical stresses, and high voltages developed during quench while providing reliable operation for extended period of time. Insulation system is one of the most important elements of magnet design, which determines (and in some cases even limits) the electrical, mechanical, and thermal performance. Different elements of the magnet insulation system such as cable insulation, interlayer insulation, quench heater insulation, and ground insulation have been developed and studied. In this paper we will describe the insulation system used in the Fermilab shell-type dipole models followed by the high voltage test results.

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.

Fermilab, in collaboration with LBNL and BNL, is developing a quadrupole for installation in the interaction region inner triplets of the LHC. This magnet is required to have an operating gradient of 215 T/m across a 70 mm coil bore, and operates in superfluid helium at 1.9 K. A 2 m magnet program addressing mechanical, magnetic, quench protection, and thermal issues associated with the design was completed earlier this year, and production of the first full length, cryostatted prototype magnet is underway. This paper summarizes the conclusions of the 2 m program, and the design and status of the first full-length prototype magnet.

A 43.5 mm aperture dipole magnet with a nominal field of 11 T is being fabricated at Fermilab. The design is based on a two-layer shell-type coil structure made of Rutherford-type Nb/sub 3/Sn cable with wind and react technology. The mechanical support structure consists of vertically split iron yoke locked by two aluminum clamps and a 8 mm thick stainless steel skin. This paper summarizes the fabrication details of the first dipole model and test results from a 2110 mm long mechanical model.

As part of the US LHC program to develop high gradient superconducting quadrupoles for the LHC interaction regions, a series of 2 meter long model magnets has been built and tested at Fermilab. This R&D program was used to refine the mechanical and magnetic design, optimize fabrication and assembly tooling and ensure adequate quench performance. The final design, fabrication, and assembly procedures developed in this program have produced magnets which meet the LHC requirements of operating at 215 T/m with excellent magnetic field harmonics. This paper summarizes the test results of the last five model magnets, including quench tests over several thermal cycles, and excitation current ramp rate and temperature dependence studies.

Fermilab has begun investigating Nb/sub 3/Sn twin aperture dipole magnet designs as a next step towards the realization of high field magnets for a Very Large Hadron Collider (VLHC). The magnet design is based on two-layer shell-type Nb/sub 3/Sn coils with 43.5 mm aperture. Two different mechanical designs were investigated, one with "cold" iron yoke and the other with "warm" iron yoke. The former has a vertically split three-piece iron yoke with a cut parallel to a flux line to reduce the transverse magnetic flux. The two outer halves are locked in place by aluminum clamps. Both the clamps and the stainless skin provide the required pre-stress to the coils. The "warm" iron yoke design consists of thick freestanding stainless steel collars with wide keys and an insert separating the two coil blocks. The paper presents both the mechanical design and analysis for the two designs.

End parts are one of the most costly components of a superconducting magnet. Therefore, efforts are underway at Fermilab to develop new technologies to reduce the fabrication time and cost of the magnet end parts. In this paper, we discuss some of the design and fabrication issues for the magnet end parts with a particular specific objective in mind.

A one meter long Nb/sub 3/Sn dipole model with 11 T nominal magnetic field in a 43.5 mm bore is being developed at Fermilab in collaboration with LBNL and KEK as part of the R&D efforts for a future Very Large Hadron Collider. This paper describes the magnet design and fabrication procedure as well as summarizes the results of magnetic, mechanical and quench protection analyses. The main parameters of superconducting strand and cable are also reported.

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.

The goal of the Fermilab high field magnet (HFM) R&D project is to explore various designs and production technology of a high-field, low-cost Nb/sub 3/Sn accelerator magnet suitable for a future Very Large Hadron Collider (VLHC). The model under fabrication consists of two-layer shell-type coil with 43.5 mm aperture and cold iron yoke. The Fermilab concept of magnet design and fabrication technology involves some specific features such as curing of half-coil with ceramic binder/matrix before reaction, and then simultaneous reaction and impregnation of both half-coils to get a "coil pipe" structure. The coil pipe is mechanically supported by the vertically-split iron yoke locked by two aluminum clamps and a thick stainless steel skin. 2D finite element analysis has been performed to study and optimize the prestress in the coil and in the structural elements at room temperature and at 4.2 K. Model description, material properties and the results of mechanical analysis are reported in this paper.

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.

Fermilab, in collaboration With LBNL and BNL, is in the process of developing a focusing quadrupole for installation in the interaction region inner triplets of the LHC. This magnet is required to have an operating gradient of 215 T/m across a 70 mm coil bore, and operates in superfluid helium at 1.9 K. The design is based on a two layer cos (20) coil, mechanically supported by standalone steel collars. The collared coil assembly is surrounded by a iron yoke for flux return, and the assembly enclosed by a stainless steel shell. The development program has addressed mechanical, magnetic, quench protection, and thermal issues, through a series of model magnets constructed at Fermilab. This paper summarizes results from the recent model tests, and the status of the program.

As a first step towards the development of a high field Nb/sub 3/Sn superconducting dipole for a Very Large Hadron Collider (VLHC), a short mechanical model was built and tested at Fermilab. The aim of this work was to develop simpler fabrication techniques and test new structural materials to use in the dipole model. The coil design was based on a two-layer, cos(B) approach. The end parts were designed using ROXIE magnet optimization program and manufactured using a 6-axis EDM machine. The two layers of each half-coil were wound using one piece of cable without any interlayer splices. After winding, a ceramic matrix was applied to the each half-coil and the coil was cured under compression at 150/spl deg/C. The two half-coils were then assembled together in a reaction fixture for heat treatment at 450/spl deg/C for 8 hours. After reaction, the coils were placed in a curing fixture for epoxy impregnation. Finally some mechanical and electrical tests were performed after which the coils were sectioned to check the cable positioning and impregnation quality. This paper summarizes the results and experience obtained from the mechanical model.

Fermilab and LBNL are in the midst of a model magnet program to develop and prove the design of quadrupoles for use in the LHC Interaction Region inner triplets. These magnets have a nominal gradient of 205 T/m in a 70 mm bore, and operate in superfluid helium at 1.9 K. The R&D program addresses magnetic, mechanical, thermal design and quench protection issues. This paper describes design, fabrication experience and test results from the first 2 m models.

A novel experimental technique has been developed that allows the recovery of specimens within which an adiabatic shear band has been grown as the result of a single torsional pulse. The technique uses a new device called the compression-torsion Kolsky bar; this is an adaptation of the classical torsional Kolsky bar in which both compression and torsion are stored in the clamped length. Recovery of the specimen is obtained by causing the transmitted compression pulse to reflect from the free end of the output bar as a tensile pulse which then causes failure of the specimen/output-bar interface. All further pulses then cause no more than rigid motions of the specimen. Thus the specimen is recovered after it has been loaded by a single torsional pulse; microscopic examination of the recovered specimen now allows the rigorous determination of the evolution of microstructure and the identification of deformation mechanisms that are active under the dynamic shear loading. As an example of the utility of this recovery technique, its application to the study of adiabatic shear localization in alpha-titanium is presented. The technique allows a systematic study of the microscopic mechanisms that drive the initiation and growth of adiabatic shear bands by recovering samples within which shear bands have been grown under controlled conditions; further characterization through sectioning, followed by optical, scanning, and transmission electron microscopy is then possible. The technique also allows one to study the influence of the shape and size of geometric defects (for example, notch tip radius and notch depth) on the initiation of adiabatic shearing failures. The effect of normal stresses on the susceptibility of a material to shear localization can also be investigated.

The high-strain-rate mechanical response of α-titanium is examined in terms of the underlying deformation mechanisms that govern its macroscopic behavior. The mechanical behavior of α-titanium has been evaluated using quasistatic (10−5 to 100 s−1) compression testing with servohydraulic machines, dynamic (10−2 to 104 s−1) compression testing with a compression Kolsky bar, and high-rate (10−4 to 105 s−1) shearing under pressure using the pressure–shear plate impact technique. At the macroscopic level, α-titanium displays substantial rate sensitivity of the flow stress and pronounced strain hardening. The strain-hardening is greater at high strain rates than at low strain rates, and increases with strain at low strain rates. In an effort to determine the deformation mechanisms underlying this macroscopic behavior, the microstructures developed after low-rate and high-rate deformations have been characterized using both optical and transmission electron microscopy (TEM). At the microscopic level, both dislocations and twins are observed; the density of twins increases with both strain and strain rate and is shown to be a unique function of the flow stress (but not vice versa). Although dislocation motion accounted for the majority of plastic deformation, twin-dislocation interactions play an important role in strain hardening. The Kocks–Mecking model is used in order to describe the mechanical response as a function of the strain, strain rate and temperature; while the model is able to predict the monotonic behavior fairly accurately, it is unable to capture the experimental behavior observed in load–unload–reload tests.

The mechanical properties of a 6061-T6 aluminum alloy reinforced with a 20 vol.% fraction of alumina particles and of an unreinforced 6061-T6 alloy are studied over a range of strain rates (10-4to 6 x 105s-1) using quasistatic compression, compression and torsion Kolsky Bars, and high strain rate pressure-shear plate impact. At a given strain rate the composite displays increased strength but essentially the same strain hardening as the matrix. However, the composite displays a stronger rate-sensitivity than does the unreinforced alloy at high rates of deformation (>103s-1). The rate-sensitivity of the unreinforced alloy is shown to be largely the result of the imposed strain rate rather than of the rate history. For quasistatic deformations, a model proposed by Bao et al. (1991) describes the behavior of the composite fairly accurately given the behavior of the unreinforced alloy. This paper presents an extension of the model that is able to predict the dynamic behavior of the composite given the dynamic response of the monolithic alloy.

The dynamic failure of an alumina particle-reinforced 6061-T6 aluminum alloy composite has been studied using a tension Kolsky bar, and the process of fracture has been investigated using scanning electron microscopy. The failure of a 6061-T6 aluminum alloy was also studied for purposes of comparison. The composite was found to fail in a macroscopically brittle manner in tension, with a failure strain that increased with the nominal strain rate. Differences in hardening rate that are observed in dynamic tension and compression are ascribed to the development of internal damage within the composite in the form of particle cracking. Examination of the fracture surface of the monolithic alloy after dynamic failure shows a ductile failure through void nucleation, growth and coalescence, with substantial void sheet formation. Examination of the fracture surface of the composite after dynamic failure shows microscopically ductile failure in the matrix following brittle cracking of the particles. The dynamic failure process is hypothesized to consist of: (a) cracking of the reinforcing particles; (b) partial debonding at the particle—matrix interface resulting in the nucleation of voids within the matrix; and (c) the growth and coalescence of voids in the matrix to form the final failure surface. The failure process itself quickly localizes within the specimen, so that only a small part of the specimen is affected by all of the damage processes of particle cracking, interface failure and void growth.

Fermilab, as part of the US-LHC Accelerator Project, has designed and is producing superconducting low-beta quadrupole magnets for the Large Hadron Collider (LHC). These 70 mm bore, 5.5 m long magnets operate in superfluid helium at 1.9 K with a maximum operating gradient of 214 T/m. Two quadrupoles, combined with a dipole orbit corrector, form a single LQXB cryogenic assembly, the Q2 optical element of the final focus triplets in the LHC interaction regions. Field quality was measured at room temperature during fabrication of the cold masses as well as at superfluid helium temperature in two thermal cycles for the first LQXB cryogenic assembly. Integral cold measurements were made with a 7.1 m long rotating coil and with a 0.8 m long rotating coil at 8 axial positions and in a range of currents. In addition to the magnetic measurements, this paper reports on the quench performance of the cold masses and on the measurements of their internal alignment.

An apparatus for the measurement, under transverse pressure, of the inter‐strand contact resistance in epoxy‐impregnated Nb3Sn Rutherford cables has been recently assembled at Fermilab. Procedures have been developed to instrument and measure samples extracted from Nb3Sn coils. Samples were extracted from coils fabricated with the Wind‐and‐React and the React‐and‐Wind technology, both presently under development at Fermilab. A ceramic binder is used to improve the insulation and to simplify the fabrication of coils using the Wind‐and‐React technology. Synthetic oil is used to prevent sintering during the heat treatment of coils to be wound after reaction. In order to evaluate the effects of the ceramic binder and of the synthetic oil on the inter‐strand resistance, measurements of samples extracted from coils were compared with measurements of cable stacks with varying characteristics. In this paper we describe the apparatus, the sample preparation, the measurement procedure, and the results of the first ...

Insulation is one of the critical components for high‐field Nb3Sn magnets that follow wind‐and‐react approach. The insulation material has to withstand high bending stresses while winding the coil and high heat‐treatment temperatures under pressure during coil reaction. At Fermilab we have developed a procedure and tested successfully the dry ceramic insulation tape with inorganic liquid binder to wind and cure the coils. Recently we have extended this to a pre‐preg ceramic insulation tape, which would minimize and control the amount of binder in the coil. Several coils with various insulation patterns have been fabricated and tested at Fermilab. This paper discusses the fabrication issues of the coils with different types of cable insulation including the pre‐preg ceramic insulation.

Fermilab is involved in the development of Nb3Sn magnets for future hadron colliders. One of the magnet design options is based on cosine‐theta coils and the wind‐and‐react approach. Three short dipole models of this type were fabricated and tested revealing serious problems in magnet quench performance. To effectively address these issues, coil tests were continued in a mirror magnet configuration, where one coil was replaced with a half‐cylinder of low carbon steel (the magnetic mirror) inside the magnet mechanical structure. This approach has reduced the fabrication cost and time as well as improved the coil instrumentation. The paper summarizes the magnetic and mechanical design of mirror magnet configuration along with fabrication details.

A short dipole model with the 10-11 T nominal field based on the Nb/sub 3/Sn superconducting strand is being developed at Fermilab in collaboration with LBNL and KEK as part of the R&D effort for VLHC. This paper describes the magnet conceptual design and parameters as well as the results of magnetic field, mechanical and quench protection calculations. Parameters of the superconducting strand and cable are also reported.

Superconducting quadrupole magnets operating in superfluid helium at 1.9 K, with 70 mm bore and nominal field gradient of 205 T/m at collision optics, are being developed by the US LHC Accelerator Project for the Interaction Regions of the Large Hadron Collider (LHC). A magnet model program to validate and optimize the design is underway. This paper reports results of field quality measurements of four model magnets.

In the recent years, Nb3Sn has been widely used for the development of high field superconducting magnets. It is known that the unreacted Nb-Sn composite undergoes a volume expansion during heat treatment due to the formation of the Nb3Sn phase. In an as-received strand this expansion is isotropic. However, an anisotropic volume expansion was observed in the Rutherford-type cable samples. A systematic study was undertaken to investigate this phenomenon and to check the hypothesis that the plastic deformation of the strands during cabling process is responsible for this behavior. Nb-Sn strands from various manufacturing technologies were rolled down to different sizes, and the resulting thickness and width of the deformed strands were measured before and after heat treatment. The results obtained on the deformed strands were then compared with those obtained from cables. A good consistency was achieved in most of the cases.

Superconducting quadrupole magnets for the interaction regions of the Large Hadron Collider are being developed by the US-LHC Accelerator Project. These 70 mm bore quadrupole magnets are intended to operate in superfluid helium at 1.9 K with a nominal field gradient of 215 T/m. A series of 2 m model magnets has been built and cold tested at Fermilab to optimize their design and construction and to study the performance of the magnets. Field measurements of the 8 model magnets and comparisons with the required field quality are reported in this paper.

The mechanical design of the Fermilab high gradient quadrupole (HGQ) magnet cold mass is presented, along with its expected behavior and performance under fabrication and operational conditions. Coil stresses, end forces and collared coil diameter measurements obtained during fabrication and cryogenic testing are also presented, and are discussed in the context of expected behavior and feedback into the design.

Fermilab and LBNL are in the midst of superconducting magnet R&D program to test and optimize the design of quadrupoles to be used in the LHC Interaction Region inner triplets. The magnets are required to deliver a 215 T/m gradient across a 70 mm aperture. Five quadrupole short models have been fabricated and four of them have been tested. This paper describes the last model design details and reports the results of the magnet quench performance study. (5 refs).

Superconducting quadrupole magnets for the interaction regions of the Large Hadron Collider are being developed by the US-LHC Accelerator Project. These 70 mm bore quadrupole magnets are intended to operate in superfluid helium at 1.9 K with a nominal field gradient of 215 T/m. A series of 2 m model magnets are being built and tested at Fermilab to optimize design and construction parameters. Measurements of the field quality of the model magnets tested to date and comparisons with the required field quality are reported in this paper.

A series of model magnets is being constructed and tested at Fermilab in order to verify the design of high gradient quadrupole magnets for the LHC interaction region inner triplets. The 2 m models are being built in order to refine the mechanical and magnetic design, optimize fabrication and assembly tooling, and ensure adequate quench performance. This has been carried out using a complementary combination of analytical and FEA modeling, empirical tests on 0.4 m mechanical assemblies and testing of model magnets during fabrication and under cryogenic conditions. The results of these tests and studies have led to improvements in the design of the magnet end restraints, to a preferred choice in coil end part material, and to a better understanding of factors affecting coil stress throughout the fabrication and operational stages.