Measurements of Passive Correction of Magnetization Higher Multipoles in One Meter Long Dipoles

L LBL--29499 DE91 OO1812 MEASUREMENTS OF PASSIVE CORRECTION OF MAGNETIZATION HIGHER MULTIPOLES IN ONE ME'/ER LONG DIPOLES M. A. Green, R. F. Althaus, P. J. Barale, R.W. Benjegerdes, W. S. Gilbert, M. I. Green, R. M. Scanlan, and C. E. Taylor Lawrence BerkeleyLaboratory University of California Berkeley, CA 94720 1990 Applied Superconductivity Conference Snowmass, CO September 24-28, 1990 *This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, U.S. Dept. of Energy, under Contract No, DE-ACO3-76SF0(O)98. £)I_r RIBUTION THIS DOCUMENTISUN!,,._b, OF

The effect of superconductor magnetization on the quality of the micron filaments and a copper-to-superconductor ratio of 1.48. The outer coil conductor has 6 micron diameter filaments and a copperfield generated within a superconducting dipole was observed as to-superconductor ratio of 1.77. The correcter for the D-15-C2 early as 1970. 1 The effect of superconductor magnetization on field dipole is also shown in Fig. 1. The cen'octet is symmetric about the quality has been modeled using complex current doublet theory. 2 midplane and the poles. Twelve 0.808 mm diameter conductors are This mathematical model has been applied to both accelerator dipole located.about the midplane and ten 0.808 mm diameter conductors and quadrupole magnets, There is good agreement between the are located at each pole. The amount of superconductor in the calculated and measured magnetization multipoles. 3 corrector represents about 1.6 percent of the superconductor in the D-15-C2 magneL The computer model has been used to calculate several methods of passive correction for accelerator dipoles. These methods include: passive superconductor,'_,5 ferromagnetic material,4,6 and oriented permanent magnet material. 4 This paper describes the Lawrence Berkeley Laboratory (LBL) passive superconductor test program. The use of passive superconductors to correct the magnetization sexmpolein a dipole magnetis not new. The concept ,ao,aOUNOR* wasf'u'st describedby BrownandFisk in 1984. 7 Fermilabreported a test of the concept in 1986.8 Passive superconductor within an accelerator dipole has the following potential advantages: 1) passive superconductor correctors are unpowered straight pieces of superconductor mounted within the magnet bore; 2) passive superconductor correction corrects magnetization muhipoles; 3) passive superconductor correction corrects the field over a wide range of inductions; 4)passive superconductor correction will, at least in part, eliminate the slow changes in the magnetization multipoles due to flux creep.9,10 The concept of passive superconductor correction was tested in • two LBL one meter long dipole magnets. The Va'stdipole had a four centimeter bore with iron far enough from the coil so that iron saturation was not an important factor at the full design field of the magnet. The second dipole has a five centimeter bore with close in i/'on.    decay rates at 1.8K and 4.3K were virtually the same both, with and without the corrector. Temperature appears to have very little effect on magnetization decay as long as it is kept constant during the decay process. The reasons why the passive corrector does not each pole and eight correct(_rs on each side at the midplane.
The completely correct the magnetization sextupole decay in the same superconductor in the corrector represents about 0.6 percent of the way the magnetization sextupole is corrected is not understood. superconductor in the D-16-B 1 magnet.
Both DESY and LBL have observed that the flux creep decay is Figure  5 shows the width of the measured sextupole different depending on the previous magnetic flux history of the magnetization curve in the D-16-BI dipole with and without the passive corrector. Figure 5 demonstrates the extent of correction by magnet.If,t2,13 The DESY flux creep decay, made without a the D-16-BI dipole correctors at the center of the magnet. The curve passive corrector, with the magnet previously charged to 3000 with correction is negative, which indicates that the corrector amperes, is about a factor of 2 smaller than when the magnet has overcorrected the magnetizal:ion sextupole. The magnitude of the been charged to 6000 amperes. The flux creep decay obse_ed.in magnetization sextupole was reduced by a factor of seven to eight, the D-16-B 1 dipole with the passive corrector snowea a simuar (The area of the magnetiza, tion sextupole hysteresis loop was reduction when peak currents were reduced from 6000 amperes to reduced by a factor of seven or eight over most of the range of 3000 amperes (see Fig. 7). As discussed above, the magnetization and decays are smaller with the passive corrector but the dependence currents.) on peak excitation still exists.
Passive Correction of Flux Cree0 De_,a_Y Figure 6 compares the decay, of the magnetization sextupole in the D:I5-C1 dipole without passive correction with the decay of the magnetization sextupole in the D-15-C2 dipole with passive The passive corrector experiments on the LBL dipoles demonstrated that correction of magnetization sextupole can be done • superconductor correction. The conductor and the coil designs are the same for the two magnets, so one would expect the two magnets with pieces of passive superconductor.
The magnetization sextupole to have the same decay without correction.
The sextupole decay is corrected by the passive superconductor at a temperature of I.'_K measured in the D-15-C1 magnet was 0.75 units per decade; the as well as 4.3K and thus reduces the temperature dependence of the corrector installed in the D-15-C2 magnet reduced the magnetization magnetization multipoles.
A reduction of the magnetization decay to +0.15 units per decade. If the flux creep magnetization sextupole was achieved when the field was decreasing as well as when the field was increasing. The decay of the magnetization decay were completely compensated for by the passive corrector, (he flux creep decay should have been about -0.15 units per decade, sextupole was not reduced to the same extent that the magnetization This estimate is based upon the reduction in the magnetization sextupol¢ (at the start of the decay) was reduced. achieved by the passive corrector before the start of the decay. This particular passive corrector is about two thirds as effective in Passive superconductor correction may be the only correction correcting the magnetization decay as it is in correcting the method which permits the SSC injection energy to be reduced substantially below 2 TeV and still have the quality of magnet field magnetization itself, needed to insure that high current proton beams can be injected and stored in the machine. --3--