W. Louie

Test Results of LARP 3.6 m

As part of the LHC Accelerator Research Program (LARP) to build a high performance quadrupole magnet with Nb3Sn conductor, a pair of 3.6 m-long Nb3Sn racetrack coils has been made at Brookhaven National Laboratory (BNL) and installed in two shell-type support structures built by Lawrence Berkeley National Laboratory (LBL). These magnet assemblies have been tested at 4.5 K at BNL to gauge the effect of extended length and prestress on the mechanical performance of the long structure compared to earlier short models. This paper presents the results of quench testing and compares the overall performance of the two versions of the support structure. We also summarize the shell strain measurements and discuss the variation of quench current with ramp rate.

{\rm Nb}_{3}{\rm Sn}

Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADCs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to ensure that eddy currents induced by the fast ramps do not impact the field quality required for successful accelerator operation.

Racetrack Coils Supported by Full-Length and Segmented Shell Structures

Several recent applications of superconducting magnets require the magnets to be operated at high ramp rates and at frequencies of several Hertz. Brookhaven National Laboratory (BNL) has recently designed and built prototypes of superconducting dipole magnets that can be ramped at a fairly high rate (1 T/s or more). For accelerator applications, it is also crucial that the magnets maintain good field quality even at high ramp rates. In order to characterize the field quality of magnets at high ramp rates, a measurement system consisting of 16 printed circuit tangential coils has been developed. The coil system is held stationary while the magnet is ramped. This paper describes the techniques used for the measurements and data analysis, and presents the results of measurements at ramp rates of up to 4 T/s in a prototype dipole built at BNL for GSI

Magnetic field measurements for fast-changing magnetic fields

Several recent applications for fast ramped magnets have been found that require precise measurement of the time-dependent fields. In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the typical level of accuracy for accelerators, /spl Delta/B/B better than 0.01%. To meet this need, we have begun development of a system containing 16 stationary pickup windings that will be sampled at a high rate. It is hoped that harmonics through the decapole can be measured with this system. Precise measurement of the time-dependent harmonics requires that both the pickup windings and the voltmeters be nearly identical. To minimize costs, printed circuit boards are being used for the pickup windings and a combination of amplifiers and ADCs for voltmeters. In addition, new software must be developed for the analysis. The paper will present a status report on this work.

Measurements of the Field Quality in Superconducting Dipoles at High Ramp Rates

Several years of experience have been acquired on the operation of probes (“moles”) constructed for the measurement of the multipole components of the magnetic fields of SSC magnets. The field is measured by rotating coils contained in a 2.4-m long tube that is pulled through the aperture of the magnet by an external device—the transporter. In addition to the measuring coils, the tube contains motors for rotating the coil and a system for sensing local vertical using gravity sensors to provide an absolute reference for the field measurements.

Development of a precise magnetic field measurement system for fast-changing magnetic fields

Brookhaven National Laboratory (BNL) has built a prototype superconducting dipole for the Facility for Antiproton and Ion Research (FAIR) at GSI that can be ramped at a high rate (1-4 T/s). To characterize the field quality at such high ramp rates, a measurement system consisting of 16 printed circuit windings was developed. In this system, the signals induced in all the windings as the magnet is ramped are analyzed to obtain the field harmonics. Initial measurements with this system suffered from somewhat poor resolution of the ADCs used for data acquisition. Also, only a few low order harmonics could be obtained with the 16 signals. These drawbacks have been addressed by replacing the ADCs with HP3458A voltmeters and by combining data taken with two different orientations of the probe. This has allowed us to measure very precisely (10 ppm of the dipole field) all the harmonics up to the 26-pole at ramp rates up to 4.3 T/s. The data analysis and results with this improved system are presented.

Performance of field measuring probes for SSC magnets

At present, functional NMR studies of metabolic processes, which require repeated images taken over a period of time, are only performed on sedated animals. This is because the axes defined by the main NMR solenoid field and the time varying gradient magnets used for spatial encoding are fixed and cannot follow the motion of an awake animal. Construction and test results will be presented for a pair of superconducting dipole coils built to make possible NMR studies of animals that are awake by providing a dynamically variable orientation of the NMR field. Each dipole coil was wound from a single cylindrical layer of Nb-Ti cable with a cos-theta distribution. One coil was wound over the other and oriented so that the fields are perpendicular. The coil pair can then produce fields in any direction perpendicular to that of the main solenoid. When powered together, the dipole and solenoid fields would allow the NMR axis to vary with time and, thus, track the motion of an awake animal. A 1 m-long pair of coils was successfully ramped to the design field, 0.08 T, at the high rate (~25 T/s) needed to track the motion. Measurements of the field quality were made during the ramping. The ramp rate studies and the magnetic field measurements are reported.