640
K. Hübner et al.
of the detectors. Furthermore, the accelerator magnets should have minimum mass
to minimize the distorions of the trajectories of scattered particles, maximizong the
detector acceptance this way and avoiding introduction of strong scattering targets
insode the detector. Thus superconducting technology without steel collaring needed
to be used. The available space for these magnets was very limited, as the detectors
already existed and could not be modified. The magnets needed to be combinded
function to separate the lepton and the hadron beam and to start focusing the
electron beam as early as possible. The aperture of the magnet needed to be very
large to allow the synchrotron beam to pass through the entire detector and lowbeta quadrupole section. Furthermore, the aperture needed to provide space for the
envelopes of the separated beams.
To meet these requirements, a new type of superconducting magnet was developed by a collaboration of scientists from Brookhaven National Laboratory and
DESY [185]. The supercnducting magnet coil was produced by developing the 2D direct wind method used for the RHIC corrector magnets to 3-D geometry such
that the superconducting wire could be attached directly to the surface of a cylinder.
The magnet coil was wound directly on the beam pipe using a seven-strand NbTi
superconducting cable and the coil was stabilized with glass-fiber tape, a technique
carried over from the HERA multipole corrector coils.
High field quality of superconducting magnets requires high precision in the
manufacturing of the coil. For the HERA interaction region magnets, the precision
was achieved by combining the RHIC and HERA corrector coil technologies.
The coil was wound on a precision-machined cylinder which was coated
with epoxy. A computer controlled stylus placed superconducting wire with high
precision on the cylinder. It also transmitted ultra-sound waves to the wire, which
by means of friction melted the epoxy surface of the cylinder thereby fixing the
superconducting wire in its position. After winding the first layer of the coil, it was
complemented with GF spacers and fixed with glass-fiber tape under high tension
before the coil was vacuum impregnated with epoxy. The field of the first layer
was measured and compared with the calculated field for perfect wire position.
Discrepancies were corrected by modifying the definition of the second layer wire
positions correspondingly. After high precision machining the new surface, the
magnet was ready for the second layer of coil to be wound. This way, the magnet
achieved very high field quality of one unit of 10 −4 at a radius of 25 mm with the
center set off by up to 20 mm.
The HERA IR magnets were operated with 4.5 K supercritical He. The performance in routine operation was excellent.
The technique of the very successful HERA low beta quadrupoles was further
developed by BNL scientists and the technique has been successfully applied to
the low beta quadrupoles of the Beijing Electron-Positron Collider BEPC-II [186],
the KEK b-factory SuperKEKB [187] and designs for the interaction regions of
the International Linear Collider [188] have bee produced and prototyped. The
Fig. 10.15 shows a photograph taken during the winding of the low-beta quadruole
for superKEKB in September 2013. This technology is now quite mature and is used
for many of the advanced eRHIC interaction region magnets [177].
K. Hübner et al.
of the detectors. Furthermore, the accelerator magnets should have minimum mass
to minimize the distorions of the trajectories of scattered particles, maximizong the
detector acceptance this way and avoiding introduction of strong scattering targets
insode the detector. Thus superconducting technology without steel collaring needed
to be used. The available space for these magnets was very limited, as the detectors
already existed and could not be modified. The magnets needed to be combinded
function to separate the lepton and the hadron beam and to start focusing the
electron beam as early as possible. The aperture of the magnet needed to be very
large to allow the synchrotron beam to pass through the entire detector and lowbeta quadrupole section. Furthermore, the aperture needed to provide space for the
envelopes of the separated beams.
To meet these requirements, a new type of superconducting magnet was developed by a collaboration of scientists from Brookhaven National Laboratory and
DESY [185]. The supercnducting magnet coil was produced by developing the 2D direct wind method used for the RHIC corrector magnets to 3-D geometry such
that the superconducting wire could be attached directly to the surface of a cylinder.
The magnet coil was wound directly on the beam pipe using a seven-strand NbTi
superconducting cable and the coil was stabilized with glass-fiber tape, a technique
carried over from the HERA multipole corrector coils.
High field quality of superconducting magnets requires high precision in the
manufacturing of the coil. For the HERA interaction region magnets, the precision
was achieved by combining the RHIC and HERA corrector coil technologies.
The coil was wound on a precision-machined cylinder which was coated
with epoxy. A computer controlled stylus placed superconducting wire with high
precision on the cylinder. It also transmitted ultra-sound waves to the wire, which
by means of friction melted the epoxy surface of the cylinder thereby fixing the
superconducting wire in its position. After winding the first layer of the coil, it was
complemented with GF spacers and fixed with glass-fiber tape under high tension
before the coil was vacuum impregnated with epoxy. The field of the first layer
was measured and compared with the calculated field for perfect wire position.
Discrepancies were corrected by modifying the definition of the second layer wire
positions correspondingly. After high precision machining the new surface, the
magnet was ready for the second layer of coil to be wound. This way, the magnet
achieved very high field quality of one unit of 10 −4 at a radius of 25 mm with the
center set off by up to 20 mm.
The HERA IR magnets were operated with 4.5 K supercritical He. The performance in routine operation was excellent.
The technique of the very successful HERA low beta quadrupoles was further
developed by BNL scientists and the technique has been successfully applied to
the low beta quadrupoles of the Beijing Electron-Positron Collider BEPC-II [186],
the KEK b-factory SuperKEKB [187] and designs for the interaction regions of
the International Linear Collider [188] have bee produced and prototyped. The
Fig. 10.15 shows a photograph taken during the winding of the low-beta quadruole
for superKEKB in September 2013. This technology is now quite mature and is used
for many of the advanced eRHIC interaction region magnets [177].