Extraction of 3D field maps of magnetic multipoles from 2D surface measurements with applications to the optics calculations of the large-acceptance superconducting fragment separator BigRIPS

Abstract The fringing fields of magnets with large apertures and short lengths greatly affect ion-optical calculations. In particular, for a high magnetic field where the iron core becomes saturated, the effective lengths and shapes of the field distribution must be considered because they change with the excitation current. Precise measurement of the three-dimensional magnetic fields and the correct application of parameters in the ion-optical calculations are necessary. First we present a practical numerical method of extracting full 3D magnetic field maps of magnetic multipoles from 2D field measurements of the surface of a cylinder. Using this novel method, we extracted the distributions along the beam axis for the coefficient of the first-order quadrupole component, which is the leading term of the quadrupole components in the multipole expansion of magnetic fields and proportional to the distance from the axis. Higher order components of the 3D magnetic field can be extracted from the leading term via recursion relations. The measurements were done for many excitation current values for the large-aperture superconducting triplet quadrupole magnets (STQs) in the BigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory. These distributions were parameterized using the Enge functions to fit the fringe field shapes at all excitation current values, so that unmeasured values are interpolated. The extracted distributions depend only on the position along the beam axis, and thus the measured three-dimensional field can easily be parameterized for ion-optical calculations. We implemented these parameters in the ion-optical calculation code COSY INFINITY and realized a first-order calculation that incorporates the effect of large and varying fringe fields more accurately. We applied the calculation to determine the excitation current settings of the STQs to realize various optics modes of BigRIPS and the effectiveness of this approach has been demonstrated.

[1]  Martin Berz,et al.  COSY INFINITY Version 9 , 2006 .

[2]  S. Kowalski,et al.  The ion-optical program raytrace☆ , 1987 .

[3]  M. Berz,et al.  Multipole expansion solution of the Laplace equation using surface data , 2006 .

[4]  S. Czajkowski,et al.  Projectile fission at relativistic velocities: a novel and powerful source of neutron-rich isotopes well suited for in-flight isotopic separation , 1994 .

[5]  M. Berz,et al.  GIOS-BEAMTRACE - A program package to determine optical properties of intense ion beams , 1987 .

[6]  Yasushige Yano,et al.  The RIKEN RI Beam Factory Project: A status report , 2007 .

[7]  G. Moloney,et al.  Design modifications to reduce duodecapole components in the fringe field region of magnetic quadrupole lenses , 1993 .

[8]  H. Feshbach,et al.  Fragmentation of relativistic heavy ions , 1973 .

[9]  I. Tanihata,et al.  Delay-line PPAC for high-energy light ions , 2001 .

[10]  T. Kubo,et al.  Magnetic Field-Map Measurement of a Superconducting Triplet Quadrupole and a Dipole Magnet for BigRIPS Separator at RIKEN , 2008, IEEE Transactions on Applied Superconductivity.

[11]  T. Kubo,et al.  Development of Parallel Plate Avalanche Counter (PPAC) for BigRIPS fragment separator , 2013, 1311.0215.

[12]  T. Nakamura,et al.  Superconducting Dipole Magnet for SAMURAI Spectrometer , 2013, IEEE Transactions on Applied Superconductivity.

[13]  A. Yoshida,et al.  Prototype of superferric quadrupole magnets for the BigRIPS separator at RIKEN , 2004, IEEE transactions on applied superconductivity.

[14]  H. Sakai,et al.  The SHARAQ spectrometer , 2012 .

[15]  G. Moloney,et al.  Measurement, analysis and modification of the fifth-order fringe field components of magnetic quadrupole lenses , 1991 .

[16]  L. Tassan-Got,et al.  Discovery and cross-section measurement of 58 new fission products in projectile-fission of 750 · A MeV 238U , 1997 .

[17]  H. A. Enge,et al.  Effect of Extended Fringing Fields on Ion-Focusing Properties of Deflecting Magnets , 1964 .

[18]  Hiroshi Suzuki,et al.  BigRIPS separator and ZeroDegree spectrometer at RIKEN RI Beam Factory , 2009 .

[19]  H. Wollnik,et al.  THIRD ORDER TRANSFER MATRICES FOR THE FRINGING FIELD OF MAGNETIC AND ELECTROSTATIC QUADRUPOLE LENSES. , 1972 .

[20]  D. Greiner,et al.  Fragmentation of N-14 nuclei at 29 GeV - Inclusive isotope spectra at 0 deg. , 1972 .

[21]  A. Yoshida,et al.  Status and Overview of Superconducting Radioactive Isotope Beam Separator BigRIPS at RIKEN , 2007, IEEE Transactions on Applied Superconductivity.

[22]  T. Kubo.  In-flight RI beam separator BigRIPS at RIKEN and elsewhere in Japan , 2003 .

[23]  T. Kuriyama,et al.  An Air-Core Type Superconducting Quadrupole Triplet for the BigRIPS Separator at RIKEN , 2008, IEEE Transactions on Applied Superconductivity.

[24]  Marco Venturini,et al.  ACCURATE COMPUTATION OF TRANSFER MAPS FROM MAGNETIC FIELD DATA , 1999 .

[25]  V. Altuzar,et al.  Atmospheric pollution profiles in Mexico City in two different seasons , 2003 .