M.I. Green

ASTROMAG: A superconducting particle astrophysics magnet facility for the space station

This paper describes a superconducting magnet system which is the heart of a particle astrophysics facility to be mounted on a portion of the proposed NASA space station. This facility will complete the studies done by the electromagnetic observatories now under development and construction by NASA. The paper outlines the selection process of the type of magnet to be used to analyze the energy and momentum of charged particles from deep space. The ASTROMAG superconducting magnet must meet all the criteria for a shuttle launch and landing, and it must meet safety standards for use in or near a manned environment such as the space station. The magnet facility must have a particle gathering aperture of at least 1 square meter steradian and the facility should be capable of resolving heavy nuclei with a total energy of 10 Tev or more.

Magnetic field decay in model SSC dipoles

LBL-25139 Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Accelerator & Fusion Research Division Presented at the 1988 Applied Superconductivity Conference, San Francisco, CA, August 21-25, 1988 Magnetic Field Decay in Model sse Dipoles W.S. Gilbert, R.F. Althaus, PJ. Barale, R.W. Benjegerdes, M.A. Green, M.l Green, and R.M. Scanlan August 1988 r Prepared for tbe U.S. Department of Energy under Contract Number DE-AC03-76SF00098.

Magnetic measurement system for harmonic analysis of LBL SSC model dipoles and quadrupoles

Specialized hardware and software developed to facilitate harmonic error analysis measurements of 1-m long Superconducting Super Collider model dipole and quadrupole magnets are described. Cold bore measurements feature cryogenic search-coil arrays with high bucking ratios that also have sufficient sensitivity to make room-temperature measurements at the low magnet currents of approximately 10 A. Three sets of search coils allow measurements of the center, either end, and/or the axially integrated field. Signals from the search coils are digitally integrated by a voltage-to-frequency converter feeding an up-down counter. The data are drift-corrected, Fourier analyzed, converted to physical quantities, and printed and plotted. A cycle of measurements including data acquisition, processing, and the generation of tabular and graphic output requires 80 s. The vast amount of data generated (several hundred measurement cycles for each magnet) has led to the development of three types of postprocessing for the dipole and quadrupole systems: (1) re-creation of the real-time output, (2) generation of an SSC prompt report, and (3) production of general-purpose spreadsheet/graphical output. >

The Effect of Flux Creep on the Magnetization Field in the SSC Dipole Magnets

The sextupole fields of model SSC dipole magnets have been observed to change with time when the magnets are held at constant current under conditions similar to injection into the SSC accelerator. The changes in the sextupole component have close to a linear log time dependence, and is felt to be caused by flux creep decay of the magnetization currents in the superconductor filaments. Measurements of this decay have been made under various conditions. The conditions include various central field inductions and changes of field prior to when the decay was measured. The measured field decay in the dipole’s sextupole is proportional to the magnitude and sign of the sextupole due to magnetization which was measured at the start of the decay. This suggests that the decay is a bulk superconductivity flux creep. Proximity coupling appears to play only a minor role in the flux creep according to recent LBL measurements with a stable power supply.

Design, fabrication and calibration of a cryogenic search-coil array for harmonic analysis of quadrupole magnets

A cryogenic search-coil array was fabricated for harmonic error analysis of Superconducting Super Collider model quadrupoles. The coil consists of three triplet of coils: the center-coil triplet is 10-cm long, and the end coil triplets are 70-cm long. Design objectives are a high bucking ratio for the dipole and quadrupole signals and utility at cryogenic operating currents (-6 kA) with sufficient sensitivity for use at room-temperature currents ( approximately 10 A). Individual coils were measured mechanically to +or-5 mu m, and their magnetic areas measured to 0.05%. A computer program was developed to predict the quadrupole and dipole bucking ratios from the mechanical and magnetic measurements. The calibration procedure and accuracy of the array are specified. Results of measurements of SSC model quadrupoles are also presented. >

Experience with measuring magnetic moments of permanent magnet blocks at Lawrence Berkeley Laboratory

Since May 1985, the Magnetic Measurements Engineering Group at Lawrence Berkeley Laboratory (LBL) has measured and sorted a total of 3834 permanent-magnet blocks. These magnetic blocks have been used in the construction of various successful accelerator beam-line elements including dipoles, quadrupoles, and wigglers. The authors report on observed variations in magnetic moments among blocks supplied by five manufacturers, describe the operational capabilities (accuracy, precision, and resolution) of the LBL Magnetic-moment Measurement and Sorting System (MMSS), cite the results of comparative calibrations by permanent-magnet manufacturers and other national laboratories, and suggest criteria for automating the MMSS for measuring the large number of permanent-magnet blocks required for the insertion devices for the projected LBL 1-2-GeV Synchrotron Radiation Source. >

New measurements of magnetic field decay in 1 meter SSC-type dipoles

Previous studies of magnetic field decay in model SSC (Superconducting Super Collider) dipoles due to changes in magnetization currents caused by flux creep have used the assumed SSC injection energy of 1 TeV, or an 0.33-T central dipole field, and an excitation to the storage field of 6.6 T. More recently, it has been decided to inject at 2 TeV, or 0.66 T and so more recent tests have been carried out at the new injection field, or at both the new and old fields. Additionally, the effects of temperature changes and excitation cycles on the field decay have been studied. The roughly log linear decay of magnetization current multipole fields has been demonstrated in several new dipoles. A suggested mechanism of thermally induced activation in the additional 0.5-K range has been effectively countered by temperature measurements that show temperature fluctuation ten to thirty times lower, over a 90-min time period.

Magnetic measurements at Lawrence Berkeley Laboratory

Recent magnetic measurement activities at LBL have been concentrated in two separate areas, electromagnets and permanent magnets for the Advanced Light Source (ALS), and superconducting magnets for the Superconducting Super Collider Laboratory (SSCL). A survey of the many different measurement systems is presented. These include AC magnetic measurements of an ALS booster dipole engineering model magnet, dipole moment measurements of permanent magnet blocks for ALS wigglers and undulators, permeability measurements of samples destined for wiggler and undulator poles, harmonic error analysis of SSC one-meter model dipoles and quadrupoles and five-meter long SSC prototype quadrupoles, harmonic error analysis of ALS dipoles, quadrupoles, and sextupoles, precision Hall probe mapping of ALS storage ring combined function magnets, and the design of the ALS insertion device magnetic mapping system. A Unix-based data acquisition system that is being developed for the SSC is also described. Probes used for magnetic measurements include Helmholtz coils, integral coils, point coils, bucking harmonic analysis coils, several different types of Hall probes, and nuclear magnetic resonance magnetometers. >

Correction of Magnetization Sextupole in One-Meter Long Dipole Magnets Using Passing Superconductor

The generation of higher multipoles due to the magnetization of the superconductor in the dipoles of the SSC is a problem during injection of the beam into the machine. The use of passive superconductor was proposed some years ago to correct the magnetization sextupole in the dipole magnet. This paper presents the LBL test results in which the magnetization sextupole was greatly reduced in two one-meter long dipole magnets by the use of passive superconductor mounted on the magnet bore tube. The magnetization sextupole was reduced a factor of five on one magnet and a factor of eight on the other magnet using this technique. Magnetization decapole was also reduced by the passive superconductor. The passive superconductor method of correction also reduced the temperature dependence of the magnetization multipoles. In addition, the drift in the magnetization sextupole due to flux creep was also reduced. Passive superconductor correction appears to be a promising method of correcting out the effects of superconductor magnetization in SSC dipoles and quadrupoles.