Magnetic Field Quality of Short Superconducting Dipole Model Magnets for LHC

A series of 1-m long, 56 mm aperture dipole models has been built and tested at CERN within the scope of the R&D program for LHC. Here we report a summary of results of warm and cold steady state field measurements in these models, concentrating on the contribution of the coil geometry. The first allowed harmonics are clearly correlated to the coil azimuthal size, and the slope of the correlation can be predicted accurately

Determination of interstrand contact resistance from loss and field measurements in LHC dipole prototypes and correlation with measurements on cable samples

Loss and field errors due to ramping in LHC accelerator dipole magnets are mainly determined by the contact resistance between the strands of the magnet cable. It is therefore important to develop cables having sufficiently high contact resistance in the magnets in order to ease operation of the future LHC collider during ramping. In this paper the contact resistance Rc and its distribution in the magnet windings are determined for several dipole prototypes using both the measured loss and field errors during ramping of the magnet. We compare these results with interstrand contact resistance measurements made on short samples of the cables used in these magnets

Power Test Results of the First LHC Second Generation Superconducting Single Aperture 1m Long Dipole Models

Within the LHC magnet research and development programme, a series of single aperture 1m long models of second generation are presently being built and tested at CERN. The main features of these magnets are: five-block, two layer coils wound from 15mm wide graded NbTi cables, enlarged 56mm aperture and all-polyimide insulation. This paper reviews the power test data of magnets tested to date in both supercritical and superfluid helium. The results of the quench training, the initial location and propagation of quenches and their sensitivity to energy extraction are presented and discussed in terms of the design parameters and the aims of this short dipole model test program

Coil Size and Geometric Field Quality in Short Model Dipoles for LHC

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

Field Quality of the Short Superconducting Dipole Models for the LHC

A full characterization of the magnetic field in warm and cold conditions was performed as a part of the standard test on the LHC 1-m long superconducting dipole models. Furthermore, dedicated measurement campaigns addressed the effect of current cycles and quenches on field quality. Powering and quenches were found to generate characteristic instabilities in the geometric harmonics. Detailed results are presented on this phenomenon, as well as correlations between warm and cold measurements and field reconstructions

A Fast Digital Integrator for Magnetic Field Measurements at CERN

A self-calibrating digital instrument for flux measurements on magnets for accelerators used in basic research on subnuclear particles is proposed. The instrument acquires voltage arising from rotating coils transducers with a theoretical resolution of 10 ppt and a maximum sampling frequency of 800 kS/s. Then, samples are integrated on-line and suitably processed in order to improve time resolution and flux accuracy. This allows the limits of state-of-the-art digital fluximeters, related mainly to newgeneration rotating coils, with trigger rate of 20 kHz and coils speed of 10 rps, to be overcome. The instrument has been prototyped at Magnetic Measurement and Testing (MTM) Group of European Laboratory for Nuclear Research (CERN), under a framework of cooperation with the University of Sannio. Details on hardware and firmware conception, as well as on experimental results of the instrument principle validation, and of the preliminary metrological characterization of the prototype, are provided

Measurement of AC Loss and Magnetic Field during Ramps in the LHC Model Dipoles

We describe the systems for AC loss and magnetic field measurements developed for the LHC superconducting magnets. AC loss measurements are performed using an electric method, while field measurements are performed using either fixed pick-ups or rotating coils. We present results obtained on 1-m long model dipoles, and compare the results of the different methods in terms of average inter-strand resistance and low order field harmonics

Further Development of the Sextupole Dipole Corrector (MSCB) Magnet for the LHC

Combined sextupole-dipole corrector magnets (MSCB) will be mounted in each half cell of the new Large Hadron Collider (LHC) being built at CERN. The dipole part, used for particle orbit corrections, will be powered individually and is designed for low current, originally 30 A but now 55 A. The sextupole part, used for chromaticity corrections, is connected via cold busbars in families of 12 or 13 magnets and is powered with 550 A. Several versions of this corrector magnet were tested as model magnets in order to develop the final design for the series. In the first design the coils are nested, with the dipole coil wound around the sextupole coil to obtain as short a magnet as possible, accepting the slight cross-talk between the coils due to persistent currents, and increased saturation effects. The design has evolved and an alternative design, in which the dipole and sextupole coils are separated, is now favored. Tests at 4.5 K and at 1.9 K were conducted to determine the training behavior, the field quality, and the cross-talk between the windings. This paper discusses the results for the different configurations

Design, Manufacturing Aspects and Performance of Recent 10 m Long Model Dipole Superconducting Magnets for the LHC Project

A number of twin aperture, 10 m long, model dipole magnets for the LHC Project have been built and tested. With regard to the models of the first generation, the inner coil diameter and the intra-beam distance were increased from 50 to 56 mm and from 180 to about 194 mm, respectively. Also with regard to the previous models, a 5-block (instead of a 6-block) coil cross-section was chosen and the wid th of the Rutherford cable was reduced from 17 mm to 15 mm. The coils were manufactured and collared in Industry, the assembly of their magnetic circuit and cold mass were carried out at CERN. The ind ividual design and manufacturing features of each of these magnets are described and the results of their warm and cold magnetic measurement are presented and discussed